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As solid-state laser technology continues to mature, high-energy lasers operating in the near-infrared (NIR) band have seen increased utilization in manufacturing, medical, and military applications. Formulations of maximum permissible exposure limits establish guidelines for the safe use of these systems for a given set of laser parameters, based on past experimental and analytical studies of exposure thresholds causing injury to the skin and eyes. The purpose of our study is to characterize the skin response to multiple-pulsed laser exposures at the NIR wavelength of 1070 nm, at a constant beam diameter of 1 cm, using anesthetized Yucatan mini-pig subjects. Our study explores three constant total laser-on times of 0.01, 0.1, and 10 s as single- and multiple-pulse sequences. Exposures consisting of 10, 30, and 100 pulses have identical individual pulse durations but different duty cycles in order to include variable degrees of thermal additivity. A plurality of three observers quantifies skin damage with the minimally visible lesion metric, judged at the 1- and 24-h intervals postexposure. Calculation of the median effective dose (ED50) provides injury thresholds for all exposure conditions, based on varying laser power across subjects. The results of this study will provide a quantitative basis for the incorporation of multiple-pulsed laser exposure into standards and augment data contained in the existing ED50 database.

In cases where a laser source produces a pattern that is asymmetric on the retina, a modeling-based approach can be used to calculate a retinal thermal response to predict damage and make meaningful comparisons to exposure limit trends. The SESE (Scalable Effects Simulation Environment) model is a full 3D thermal finite-volume model that can simulate multiple independently controlled laser sources with unique wavelength, spatial profile, pulse duration, and power. The model is well suited to evaluate asymmetric sources since there is not an assumed axial symmetry and the spatial profile of the laser can be adjusted as a function of time. Several examples of asymmetric sources include multi-fiber bundle exposures, scanning beams, and scintillating sources. We use the SESE model to predict trends in retinal injury threshold for these cases and to help inform the laser safety community by providing estimates for safe and unsafe levels of exposure. We also introduce factors that inform hazard levels based on relative exposure conditions.In cases where a laser source produces a pattern that is asymmetric on the retina, a modeling-based approach can be used to calculate a retinal thermal response to predict damage and make meaningful comparisons to exposure limit trends. The SESE (Scalable Effects Simulation Environment) model is a full 3D thermal finite-volume model that can simulate multiple independently controlled laser sources with unique wavelength, spatial profile, pulse duration, and power. The model is well suited to evaluate asymmetric sources since there is not an assumed axial symmetry and the spatial profile of the laser can be adjusted as a function of time. Several examples of asymmetric sources include multi-fiber bundle exposures, scanning beams, and scintillating sources. We use the SESE model to predict trends in retinal injury threshold for these cases and to help inform the laser safety community by providing estimates for safe and unsafe levels of exposure. We also introduce factors that inform hazard levels based on ...

Computational models are capable of quantifying the expected thermal response of biological tissue to laser irradiation. A typical laser-tissue model accounts for optical energy deposition, heat transfer, and damage assessment, with the later often represented by calculation of the Arrhenius integral. Previous studies have successfully employed these methods to predict skin damage thresholds at laser wavelengths with high absorption in water, and usually for single continuous-wave exposures. However, there remains a need for a robust and accurate predictive model in low-absorption, high-scattering cases, such as for lasers in the near-infrared (NIR) region near 1 µm, where a large volume of tissue is heated simultaneously. This study presents a framework for modeling laser irradiation of skin tissue at 1070-nm for both continuous-wave and pulsed exposures with durations ranging from 10−2 to 101 seconds. We report the modeled skin thermal responses alongside thermal camera recordings of in-vivo porcine exposures as validation of simulation integrity. Comparisons of modeled damage thresholds calculated by the Arrhenius integral with past experimentally-determined minimum visible lesion ED50 data demonstrate a high degree of accuracy. The techniques outlined by this study provide a useful tool in assessing potentially hazardous near-infrared laser exposure scenarios while informing future investigations into modeling skin laser exposure at these wavelength regions.Computational models are capable of quantifying the expected thermal response of biological tissue to laser irradiation. A typical laser-tissue model accounts for optical energy deposition, heat transfer, and damage assessment, with the later often represented by calculation of the Arrhenius integral. Previous studies have successfully employed these methods to predict skin damage thresholds at laser wavelengths with high absorption in water, and usually for single continuous-wave exposures. However, there remains a need for a robust and accurate predictive model in low-absorption, high-scattering cases, such as for lasers in the near-infrared (NIR) region near 1 µm, where a large volume of tissue is heated simultaneously. This study presents a framework for modeling laser irradiation of skin tissue at 1070-nm for both continuous-wave and pulsed exposures with durations ranging from 10−2 to 101 seconds. We report the modeled skin thermal responses alongside thermal camera recordings of in-vivo porcine exp...

Computational models are capable of simulating the expected thermal response of biological tissue to laser irradiation. A typical laser tissue model accounts for optical energy deposition, heat transfer, and damage assessment, with the latter often represented by calculation of the Arrhenius integral. Previous studies have successfully employed these methods to predict skin damage thresholds at laser wavelengths with high absorption in water, and usually for single continuous-wave exposures. However, there remains a need for a robust and accurate predictive model in low-absorption, high-scattering cases, such as for exposures in the near-infrared region near 1000 nm. This study presents a framework for modeling laser irradiation of skin tissue at 1070 nm for both continuous-wave and pulsed exposures with durations ranging from 10−2 to 101 s. The authors derive an optical absorption coefficient for the epidermis that agrees with expected chromophore distribution and report the modeled skin thermal responses alongside surface thermography data from in vivo porcine exposures as validation of simulation accuracy. Comparisons of modeled damage thresholds calculated by the Arrhenius integral with documented experimentally determined minimum visible lesion ED50 data exhibit a high degree of agreement. The authors also provide new Arrhenius rate process coefficients of A = 2.74 × 1094 s−1 and Ea = 5.90 × 105 J/mol, determined from experimental thermal profiles with a unique method, that demonstrate more accurate threshold predictions than those used in previous modeling studies. The techniques outlined by this study provide a useful tool in assessing potentially hazardous near-infrared laser exposure scenarios.

Pulsed high-energy lasers operating in the near-infrared (NIR) band are increasingly being used in medical, industrial, and military applications, but there are little available experimental data to characterize their hazardous effects on skin tissue. The current American National Standard for the Safe Use of Lasers (ANSI Z136.1-2014) defines the maximum permissible exposure (MPE) on the skin as either a single-pulse or total exposure time limit. This study determined the minimum visible lesion (MVL) damage thresholds in Yucatan miniature pig skin for the single-pulse case and several multiple-pulse cases over a wide range of pulse repetition frequencies (PRFs) (10, 125, 2,000, and 10,000 Hz) utilizing nanosecond-scale pulses (10 or 60 ns). The thresholds are expressed in terms of the median effective dose (ED50) based on varying individual pulse energy with other laser parameters held constant. The results confirm a decrease in MVL threshold as PRF increases for exposures with a constant number of pulses, while also noting a PRF-dependent change in the threshold as a function of the number of pulses. Furthermore, this study highlights a change in damage mechanism to the skin from melanin-mediated photomechanical events at high irradiance levels and few numbers of pulses to bulk tissue photothermal additivity at lower irradiance levels and greater numbers of pulses. The observed trends exceeded the existing exposure limits by an average factor of 9.1 in the photothermally-damaged cases and 3.6 in the photomechanicallydamaged cases.

Coupled-cavity lasers have attracted wide attention in the past, in particular for telecommunication applications where their wavelength tunability and ability for side mode suppression are desirable. The inherent sensitivity of these devices to changes in the optical coupling has also led to their proposed use in optical sensing systems. Small changes to the refractive index of the coupler section can lead to shifts in the resonance frequency of the laser. Here we present an alternative approach to coupled-cavity sensing that exploits changes to the imaginary part of the refractive index of the coupler. An optical loss, introduced to the cavity by the passage of micro-particles, influences the optical loss of the lasing mode and changes the threshold gain requirement of the laser. The sub-linear nature of the gain-current density characteristics of the quantum confined gain medium amplifies this effect, producing an even larger perturbation in output power. We demonstrate this sensing mechanism using a monolithic coupled-cavity particle detector with on-chip capillary fill microfluidics and an in-line photo-detector section for photo-voltage transduction. Both laser and detector are pulsed allowing for a time-resolved measurement to be taken.

The integration of multiple optical elements on a common substrate to create photonic integrated circuits (PIC) has been successfully applied in: fibre-optic communications, photonic computing and optical sensing. The push towards III-Vs on silicon promises a new generation of integrated devices that combine the advantages of both integrated electronics and optics in a single substrate. III-V edge emitting laser diodes offer high efficiency and low threshold currents making them ideal candidates for the optically active elements of the next generation of PICs. Nevertheless, the highly divergent and asymmetric beam shapes intrinsic to these devices limits the efficiency with which optical elements can be free space coupled intra-chip; a capability particularly desirable for optical sensing applications e.g. [1]. Furthermore, the monolithic nature of the integrated approach prohibits the use of macroscopic lenses to improve coupling. However, with the advent of 3D direct laser writing, three dimensional lenses can now be manufactured on a microscopic-scale [2], making the use of micro-lens technology for enhanced free space coupling of integrated optical elements feasible. Here we demonstrate the first use of 3D micro-lenses to improve the coupling efficiency of monolithically integrated lasers. Fabricated from IP-dip photoresist using a Nanoscribe GmbH 3D lithography tool, the lenses are embedded directly onto a structured GaInP/AlGaInP substrate containing arrays of ridge lasers free space coupled to one another via a 200 μm air gap. We compare the coupling efficiency of these lasers with and without micro-lenses through photo-voltage and beam profile measurements and discuss optimisation of lens design.

Laser-induced microcavitation refers to the rapid formation and expansion of a vapor bubble inside the bio-tissue when it is exposed to intense, pulsed laser energy. With the associated microscale dissection occurring within the tissue, laserinduced microcavitation is a common approach for high precision bio-surgeries. For example, laser-induced microcavitation is used for laser in-situ keratomileusis (LASIK) to precisely reshape the midstromal corneal tissue through excimer laser beam. Multiple efforts over the last several years have observed unique characteristics of microcavitions in biotissues. For example, it was found that the threshold energy for microcavitation can be significantly reduced when the size of the biostructure is increased. Also, it was found that the dynamics of microcavitation are significantly affected by the elastic modules of the bio-tissue. However, these efforts have not focused on the early events during microcavitation development. In this study, a direct numerical simulation of the microcavitation process based on equation of state of the biotissue was established. With the direct numerical simulation, we were able to reproduce the dynamics of microcavitation in water-rich bio tissues. Additionally, an experimental setup in deionized water and 10% PAA gel was made to verify the results of the simulation for early micro-cavitation formation for 10% Polyacrylamide (PAA) gel in deionized water.

With continued advancement of solid-state laser technology, high-energy lasers operating in the near-infrared (NIR) band are being applied in an increasing number of manufacturing techniques and medical treatments. Safety-related investigations of potentially harmful laser interaction with skin are commonplace, consisting of establishing the maximum permissible exposure (MPE) thresholds under various conditions, often utilizing the minimally-visible lesion (MVL) metric as an indication of damage. Likewise, characterization of ablation onset and velocity is of interest for therapeutic and surgical use, and concerns exceptionally high irradiance levels. However, skin injury response between these two exposure ranges is not well understood. This study utilized a 1070-nm Yb-doped, diode-pumped fiber laser to explore the response of excised porcine skin tissue to high-energy exposures within the supra-threshold injury region without inducing ablation. Concurrent high-speed videography was employed to assess the effect on the epidermis, with a dichotomous response determination given for three progressive damage event categories: observable permanent distortion on the surface, formation of an epidermal bubble due to bounded intra-cutaneous water vaporization, and rupture of said bubble during laser exposure. ED50 values were calculated for these categories under various pulse configurations and beam diameters, and logistic regression models predicted injury events with approximately 90% accuracy. The distinction of skin response into categories of increasing degrees of damage expands the current understanding of high-energy laser safety while also underlining the unique biophysical effects during induced water phase change in tissue. These observations could prove useful in augmenting biothermomechanical models of laser exposure in the supra-threshold region.

A numerical analysis capable of describing the early stage of a thermal microcavitation process in a water-rich biotissue without avalanche breakdown was developed. The analysis successfully reproduced the laser-induced heating, vapor bubble formation, bubble expansion, and shockwave propagation inside a water-rich biotissue during a thermal microcavitation process. Based on the analysis, it was determined that the evolution of the temperature, pressure, and laser-induced shockwave is dependent on the incident laser energy and laser pulse width. On the other hand, the early stage dynamics of the microcavitation process showed little dependence on the elastic modulus of the biotissue for the laser and tissue conditions studied.

As solid-state laser technology continues to mature, high-energy lasers operating in the near-infrared (NIR) band are increasingly being utilized in manufacturing, medical, and military applications. Guidelines for the safe use of these systems have been established as formulations of maximum permissible exposure (MPE) limits for a given set of laser parameters, based on past experimental studies of exposure thresholds causing injury to the skin and eyes. However, in the case of skin, these formulations do not take into account the pulse characteristics of the exposure and only utilize the total exposure duration when calculating the MPE. The purpose of this study was to characterize the skin response to multiple-pulsed high-energy laser exposure at the NIR wavelength of 1070 nm, at a constant beam diameter of 1 cm, and using anesthetized Yucatan mini-pig subjects. A constant total laser-on time was explored as single- and multiple-pulse sequences. Multiple-pulse exposures had identical individual pulse durations, and different duty cycles were employed in order to characterize the effect of variable thermal additivity. Skin damage was quantified by the minimally visible lesion (MVL) metric as judged by a plurality of three observers at the 24-hour interval post-exposure. Injury thresholds for all exposure conditions were calculated as the median effective dose (ED50), based on varying laser power across subjects. The results of this study will provide a quantitative basis for the incorporation of multiple-pulsed laser exposure into existing standards and augment data contained in the existing ED50 database.As solid-state laser technology continues to mature, high-energy lasers operating in the near-infrared (NIR) band are increasingly being utilized in manufacturing, medical, and military applications. Guidelines for the safe use of these systems have been established as formulations of maximum permissible exposure (MPE) limits for a given set of laser parameters, based on past experimental studies of exposure thresholds causing injury to the skin and eyes. However, in the case of skin, these formulations do not take into account the pulse characteristics of the exposure and only utilize the total exposure duration when calculating the MPE. The purpose of this study was to characterize the skin response to multiple-pulsed high-energy laser exposure at the NIR wavelength of 1070 nm, at a constant beam diameter of 1 cm, and using anesthetized Yucatan mini-pig subjects. A constant total laser-on time was explored as single- and multiple-pulse sequences. Multiple-pulse exposures had identical individual pulse d...

Computational modeling of laser-tissue interaction in the retina can be used to predict the thermal response to a laser exposure. For in vivo photochemical damage threshold experiments, where temperature rise in retinal tissue cannot be conveniently measured, modeling was used to predict retinal temperature response. Laser exposures from sixteen in vivo experiments with wavelengths in the visible band were selected to represent a wide range of powers and exposure durations. It is hypothesized that photochemical damage mechanisms were responsible for changes to subjects’ retinal tissue and that thermal response is not a significant contribution to this observed damage.Results from the model predicted peak temperature responses of less than one Kelvin in the RPE layer of the retina where the largest temperature rise would be expected. These findings support the claim that changes to retinal tissue were not directly caused by a thermally induced mechanism.Computational modeling of laser-tissue interaction in the retina can be used to predict the thermal response to a laser exposure. For in vivo photochemical damage threshold experiments, where temperature rise in retinal tissue cannot be conveniently measured, modeling was used to predict retinal temperature response. Laser exposures from sixteen in vivo experiments with wavelengths in the visible band were selected to represent a wide range of powers and exposure durations. It is hypothesized that photochemical damage mechanisms were responsible for changes to subjects’ retinal tissue and that thermal response is not a significant contribution to this observed damage.Results from the model predicted peak temperature responses of less than one Kelvin in the RPE layer of the retina where the largest temperature rise would be expected. These findings support the claim that changes to retinal tissue were not directly caused by a thermally induced mechanism.

Optical imaging of fast events and processes is essential for understanding dynamics of complex systems. A bright flash of illuminating light is required to acquire sufficient number of photons for superior image quality. Laser pulses can provide extreme brightness and are typically employed to achieve high temporal resolution; however, the high degree of coherence associated with the lasing process degrades the image quality with speckle formation. Random lasers are low-coherence sources of stimulated emission and do not suffer from speckle, but are rather broadband and have a relatively low output power limiting the scope of their potential applications. In this report, we demonstrate the use of random Raman lasing as a novel imaging light source with unprecedented brightness for a speckle-free and narrowband light source. We showcase the advantages of a random Raman laser to image the nanosecond scale dynamics of cavitation formation in water and quantitatively compare these images to those taken with incoherent fluorescent emission and coherent laser light as illumination source.

Low cost, portable chip based flow cytometry has great potential for applications in resource poor and point of care settings. Typical approaches utilise low cost silicon or glass substrates with light emission and detection performed either off-chip using external equipment or incorporated on-chip using ‘pick and place’ diode lasers and photo-detectors. The former approach adds cost and limits portability while the sub-micron alignment tolerances imposed by the application make the latter impractical for all but the simplest of systems. Use of an optically active semiconductor substrate, on the other hand, overcomes these limitations by allowing multiple laser/detector arrays to be formed in the substrate itself using high resolution lithographic techniques. The capacity for multiple emitters and detectors on a single chip not only enables parallel measurement for increased throughput but also allows multiple measurements to be performed on each cell as it passes through the system. Several different experiments can be performed simultaneously and throughput demand can be reduced with the facility for error checking. Furthermore, the fast switching times inherent with semiconductor lasers allows the active sections of the device to be reconfigured on a sub-microsecond time scale providing additional functionality. This is demonstrated here in a capillary fill system using pairs of laser/detectors that are operated in pulsed mode and alternated between lasing and detecting in an interleaved manner. Passing cells are alternately interrogated from opposing directions providing information that can be used to correct for differences in lateral cell position and ultimately differentiate blood cell type. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Wide-field microscopy, where full images are obtained simultaneously, is limited by the power available from speckle-free light sources. Currently, the vast majority of wide-field microscopes use either mercury arc lamps, or LEDs as the illumination source. The power available from these sources limits wide-field fluorescent microscopy to tens of microseconds temporal resolution. Lasers, while capable of producing high power and short pulses, have high spatial coherence. This leads to the formation of laser speckle that makes such sources unsuitable for wide-field imaging applications. Random Raman lasers offer the best of both worlds by producing laser-like intensities, short, nanosecond-scale, pulses, and low spatial coherence, speckle-free, output. These qualities combine to make random Raman lasers 4 orders of magnitude brighter than traditional wide-field microscopy light sources. Furthermore, the unique properties of random Raman lasers make possible the entirely new possibilities of wide-field fluorescence lifetime imaging or wide-field Raman microscopy. We will introduce the relevant physics that give rise to the unique properties of random Raman lasing, and demonstrate early proof of principle results demonstrating random Raman lasing emission being used as an imaging light source. Finally, we will discuss future directions and elucidate the benefits of using random Raman lasers as a wide-field microscopy light source.

Anderson localization, also known as strong localization, is the absence of diffusion in turbid media resulting from wave interference. The effect was originally predicted for electron motion, and is widely known to exist in systems of less than 3 dimensions. However, Anderson localization of optical photons in 3 dimensional systems remains an elusive and controversial topic. Random Raman lasing offers the unique combination of large gain and virtually zero absorption. The lack of absorption makes long path length, localized modes preferred. The presence of gain offsets what little absorption is present, and preferentially amplifies localized modes due to their large Q factors compared with typical low Q modes present in complex media. Random Raman lasers exhibit several experimentally measured properties that diverge from classical, particle-like, diffusion. First, the temporal width of the emission being 1 to a few nanoseconds in duration when it is pumped with a 50 ps laser is a full order of magnitude longer than is predicted by Monte Carlo simulations. Second, the random Raman laser emission is highly multi-mode, consisting of hundreds of simultaneous lasing modes. This is in contrast to early theoretical results and back of the envelope arguments that both suggest that only a few modes should be present. We will present the evidence that suggests a divergence from classical diffusion theory. One likely explanation, that is consistent with all of these anomalies, is the presence of high-Q localized modes consistent with Anderson localization.

Skin injury response to near-infrared (NIR) laser radiation between the minimum visible lesion threshold and ablation onset is not well understood. This study utilizes a 1070-nm diode-pumped Yb-fiber laser to explore the response of excised porcine skin to high-energy exposures in the suprathreshold injury region without inducing ablation. Concurrent high-speed videography is employed to determine a dichotomous response for three progressive damage categories: observable surface distortion, surface bubble formation due to contained intracutaneous water vaporization, and surface bubble rupture during exposure. Median effective dose (ED50) values are calculated in these categories for 3- and 100-ms pulses with beam diameters (1 / e2) of 3 mm (28, 35, and 49 J / cm2) and 7 mm (96, 141, and 212 J / cm2), respectively. Double-pulse cases are secondarily investigated. Experimental data are compared with the maximum permissible exposure limits and ablation onset simulated by a one-dimensional multiphysics model. Logistic regression analysis predicted injury events with ∼90 % of accuracy. The distinction of skin response into progressive damage categories expands the current understanding of high-energy laser safety while underlining the unique biophysical effects during induced water phase change in tissue. These results prove to be useful in the diagnosis and treatment of NIR laser injuries.

Exposure of retinal tissue to a laser source requires two conditions: the person must be exposed to the laser beam and the laser must be in his/her optical field-of-view. The authors have developed a probabilistic model for the second condition. This model is based on random eye movements, known as saccades, about a look direction. This direction is an input to the model and is known either from head orientation or a task. The model calculates the instantaneous probability that the laser is in the optical field-of-view of the retinal tissues of fovea, macula, and retina. Because of saccades, the location of exposure will change several times a second. The duration of laser exposure for the look direction is then used to calculate the probability that the retinal tissue is exposed at least once, based on independent exposures from the saccades. The concepts and equations of the model are presented, along with example calculations from applying the model to a specific exposure scenario. For a given retinal tissue optical field-of-view, the primary contributor to the probability of exposure is the angle between the look direction and the laser.Exposure of retinal tissue to a laser source requires two conditions: the person must be exposed to the laser beam and the laser must be in his/her optical field-of-view. The authors have developed a probabilistic model for the second condition. This model is based on random eye movements, known as saccades, about a look direction. This direction is an input to the model and is known either from head orientation or a task. The model calculates the instantaneous probability that the laser is in the optical field-of-view of the retinal tissues of fovea, macula, and retina. Because of saccades, the location of exposure will change several times a second. The duration of laser exposure for the look direction is then used to calculate the probability that the retinal tissue is exposed at least once, based on independent exposures from the saccades. The concepts and equations of the model are presented, along with example calculations from applying the model to a specific exposure scenario. For a given retinal ...

We propose and experimentally demonstrate a new coherent anti-Stokes Raman scattering setting, which relies on a coherent excitation of Raman vibration using a broadband ultrashort laser pulse and signal read-out using a conventional continuous wave laser radiation. Such an exotic arrangement does not require any synchronization of two laser sources and can be used for direct comparison of amplitudes of nonlinear and spontaneous Raman signals. Ex-CARS in time- (top panel) and frequency- (bottom panel) domain.

A custom confocal imaging system was built and used to record a probe beam's spatiotemporal response to a thermal lens induced by a near-IR laser radiation source in a water-filled artificial eye. The IR laser radiation input power levels were varied between 150 and 890 mW at wavelengths of 1110, 1130, 1150 and 1318 nm in order to determine the strength of the resulting thermal lens as a function of time, input power, and wavelength. A high-frame-rate camera captured the probe beam's logarithmic excitation and exponential decay caused by the thermal lens (supplemental video data are provided). Data showed that for equivalent input powers and beam geometries, thermal lensing was strongest for the 1150-nm laser radiation wavelength followed by 1130, 1318 and 1110 nm.

Stimulated Raman scattering as a promising way of expanding the tunability of ultrafast lasers and as an exciting new biomedical imaging modality capable of selective excitation and chemically-specific diagnostics of molecular species.

Background and Objectives Retinal damage thresholds from 100-millisecond exposures to laser radiation for wavelengths between 1,100 and 1,350 nm have never previously been established. We sought to determine the retinal damage threshold for 100-millisecond exposures of near-infrared (NIR) laser radiation wavelengths at 1,110, 1,130, 1,150, and 1,319 nm. These data were then used to create trends for retinal damage thresholds over the 1,100–1,350 nm NIR region based upon linear absorption of laser radiation in ocular media and chromatic dispersion of the eye. Materials and Methods The paramacula and macula areas of the retina in Macaca mulatta (rhesus) subjects were exposed for 100 milliseconds to NIR laser radiation wavelengths using a Coherent OPO laser for 1,110, 1,130, and 1,150 nm and a Lee laser for 1,319 nm. Probit analysis was used to establish the estimated damage threshold in the retina for 50% of exposures (ED50). Using trends of transmitted energy to the retina, refractive error of the eye and linear absorption of the retina, a scaling factor (SF) method was created to fit the experimental data, predicting retinal damage thresholds over the 1,100–1,350 nm region. Results The experimental retinal damage threshold, ED50, for 100-millisecond exposures for laser radiation wavelengths at 1,110, 1,130, and 1,319 nm were determined to be 193, 270, and 13,713 mW of power delivered to the cornea, respectively. The retinal damage threshold for the 1,150 nm wavelength was statistically undetermined due to laser-power limitations, but was achieved in one out of three subjects tested. Conclusion The SF predicts the experimental 100- millisecond NIR ED50 value for wavelengths between 1,100 and 1,350 nm. Lasers Surg. Med. 41:382–390, 2009. © 2009 Wiley-Liss, Inc.

With high-energy lasers, not only the direct laser beam can pose significant eye and skin hazards, but also light reflecting off material illuminated by the beam. Proper hazard analysis for a material irradiated by a laser relies upon the reflecting properties of the material surface, as these properties determine the magnitude and direction of the reflected laser energy commonly characterized by the bidirectional reflectance distribution function (BRDF). However, a high-energy laser heating and possibly melting a material can change the reflecting properties of that material, so these changes must be included in the hazard analysis. Traditional methods for measuring the BRDFs of materials are not practical for measurement of materials with rapidly-changing surface properties. However, BRDF measurement by imagery of a witness screen allows for practical measurements of the dynamically-changing BRDFs of materials under high-energy laser irradiation. Using this technique, the dynamic BRDFs of stainless stee...

The current national consensus standard for laser safety in the United States is the American National Standard for Safe Use of Lasers (ANSI Z136.1). The most recent standard, Z136.1-2000, incorporates a wealth of recent bioeffects data and established a number of new maximum permissible exposure (MPE) limits for laser safety. The standard also includes recent procedures for the computation of MPE values from large or extended diffusely scattering sources, which must be understood by health physicists, laser safety officers, and others in the field of occupational safety. Here we present the fourth in a series of tutorial articles, written to clarify laser safety analysis procedures under this standard, with an emphasis on the MPE computation methods related to extended sources, and the determination of nominal hazard zones.

The potential of the device is demonstrated through the results of a micro-bead counting experiment. A 0.5 µl sample volume containing 10 µm polystyrene micro-beads in Dl water is deposited into an on-chip inlet reservoir from where it flows, under capillary action, through a buried flow cell. A laser on one side of the cell is forward biased and the opposing laser is operated as a photodiode (Fig. 2(a)). Both are pulsed to provide sub-µs time-resolution of bead transit ‘events’ with a 30 mV noise floor that affords a large dynamic range of over 1.2 V (Fig. 2(b)). After passing through the flow cell the sample fluid is drawn into a spiral patterned exit reservoir that provides sufficient pull through to sustain a continuous flow for over 30 s with flow rate of > 4mm/s.

Melanosome microcavitation is the threshold-level retinal pigment epithelium (RPE) damage mechanism for nanosecond (ns) pulse exposures in the visible and near-infrared (NIR). Thresholds for microcavitation of isolated bovine RPE melanosomes were determined as a function of temperature (20 to 85°C) using single ns laser pulses at 532 and 1064 nm. Melanosomes were irradiated using a 1064-nm Q-switched Nd:YAG (doubled for 532-nm irradiation). For comparison to melanosome data, a similar temperature (20 to 65°C) dependence study was also performed for 532 nm, ns pulse exposures of black polystyrene microbeads. Results indicated a decrease in the microcavitation average radiant exposure threshold with increasing sample temperature for both 532- and 1064-nm single pulse exposures of melanosomes and microbeads. Threshold data and extrapolated nucleation temperatures were used to estimate melanosome absorption coefficients in the visible and NIR, and microbead absorption coefficients in the visible, indicating that melanin is a better absorber of visible light than black polystyrene. The NIR melanosome absorption coefficients ranged from 3713 cm−1 at 800 nm to 222 cm−1 at 1319 nm. These data represent the first temperature-dependent melanosome microcavitation study in the NIR and provide additional information for understanding melanosome microcavitation threshold dependence on wavelength and ambient temperature.

Currently, no light source exists which is both narrow-band and speckle-free with sufficient brightness for full-field imaging applications. Light emitting diodes (LEDs) are excellent spatially incoherent sources, but are tens of nanometers broad. Lasers on the other hand can produce very narrow-band light, but suffer from high spatial coherence which leads to speckle patterns which distort the image. Here we propose the use of random Raman laser emission as a new kind of light source capable of providing short-pulsed narrow-band speckle-free illumination for imaging applications.

Thresholds for microcavitation of isolated bovine retinal melanosomes were determined as a function of temperature using single nanosecond laser pulses at 532 nm and 1064 nm. Melanosomes were irradiated using a 1064-nm Qswitched Nd:YAG (doubled for 532-nm irradiation). Time-resolved microscopy was accomplished by varying the delay between the irradiation beam and an illumination beam allowing stroboscopic imaging of microcavitation events. Results indicated a decrease in microcavitation fluence threshold with increasing sample temperature for both 532-nm and 1064-nm single pulse exposures. The nucleation temperature at both wavelengths was extrapolated through the linear relationship between the temperature increases and the decrease in fluence threshold. In addition, absorption coefficients of melanosomes for visible and near-infrared wavelengths were estimated using the calculated nucleation temperatures.

The time-temperature effects of laser radiation exposure are investigated as a function of wavelength. We experimentally measure the thermal response of tissue to laser radiation ranging in wavelength from 1100 nm to 1550 nm. Simulations were then performed to estimate damage thresholds.

Laser damage thresholds were determined for expos ure to 2.5-ms 532-nm pulses in an established in vitro retinal model. Single and multiple pulses (10, 100, 1000) were delivered to the cultured cells at three different pulse repetition frequency (PRF) values, and overt damage (membrane breach) was scored 1 hr post laser exposure. Trends in the damage data within and across the PRF range identified significant thermal additivity as PRF was increased, as evidenced by drastically reduced threshold values (< 40% of single-pulse value). Microthermography data that were collected in real time during each exposu re also provided evidence of thermal additivity between successive laser pulses. Using thermal profiles simulated at high temporal resolution, damage threshold values were predicted by an in-house computational model. Our simulated ED 50 value for a single 2.5-ms pulse was in very good agreement with experimental results, but ED 50 predictions for multiple-pulse trains will require more refinement. Keywords: laser-induced damage, retinal pigment epithelial cells, damage threshold, microthermography, computational model

Random Raman laser emission is demonstrated to be an excellent source of narrow-band, high intensity, short duration light for speckle-free imaging. Spatial coherence measurement and strobe photography of cavitation bubbles are presented.

Recent changes in the maximum permissible exposure limits (MPE) for near-infrared (NIR) laser exposures are analysed in light of nonlinear optical phenomena. We have evaluated the thresholds for supercontinuum generation for ultrashort laser exposures in the NIR and compared these with the MPE’s. Because of the strong increase in ocular absorption in the 1.2 to 1.4 micrometer range, evaluation of this phenomenon is necessary because any shift in laser energy in the eye to shorter wavelengths could lead to unforeseen increases in hazards for the retina. Trends will be discussed regarding proposed changes to the safe exposure limits in the NIR regime.

Reflection of a laser beam from a surface depends on the optical properties of the surface, and can have components that are diffuse (in all directions) or specular (in one direction). Hazard distances tend to be short and easily calculated for diffuse reflections. However, specular reflections have longer hazard distances and their calculation poses challenges due to the spatial and temporal characteristics of the reflected beam. We have developed and refined a methodology to calculate hazard distances from specular reflections. This methodology uses analytical expressions to determine the irradiance and exposure time of the reflected beam, from which hazard distances are calculated. The method accounts for the properties of the incident beam, the material reflecting properties, and the shape of the surface.The motivations and concepts of the specular methodology are presented, along with the equations resulting from this approach. The spatial and temporal characteristics of the reflected beam for a specific laser and surface are calculated from the application of these equations. These characteristics are then used to determine either localization of hazardous regions in the surrounding space or a description of possible hazards at specific locations. Examples of the application of the specular methodology are presented with their corresponding hazardous conditions.Reflection of a laser beam from a surface depends on the optical properties of the surface, and can have components that are diffuse (in all directions) or specular (in one direction). Hazard distances tend to be short and easily calculated for diffuse reflections. However, specular reflections have longer hazard distances and their calculation poses challenges due to the spatial and temporal characteristics of the reflected beam. We have developed and refined a methodology to calculate hazard distances from specular reflections. This methodology uses analytical expressions to determine the irradiance and exposure time of the reflected beam, from which hazard distances are calculated. The method accounts for the properties of the incident beam, the material reflecting properties, and the shape of the surface.The motivations and concepts of the specular methodology are presented, along with the equations resulting from this approach. The spatial and temporal characteristics of the reflected beam for a spec...

Near infrared characterization of optical properties of aqueous humor and vitreous humor of healthy human and bovine eyes has been performed. The indices of refraction (n) of these ocular tissues were determined using a Michelson interferometer. The total diffuse reflection (R (d)) and total transmission (T (t)) measurements had been taken for individual ocular tissue by using a double-integrating sphere setup and infrared laser diodes. The inverse adding doubling (IAD) computational method based on the diffusion approximation and radiative transport theory was applied to the measured values of n, R (d), and T (t) to calculate the optical absorption and scattering coefficients of the human and bovine ocular tissues. The scattering anisotropy value was determined by iteratively running the IAD method program and a Monte Carlo simulation of light-tissue interaction until the minimum difference in experimental and computed value for T (t) was realized. A comparison between the optical characterization of human and bovine ocular samples was also made.

Multiwavelength laser exposures pose unique safety challenges for both laser experts and users of laser systems. We describe two methods of optimizing optical density requirements for multiwavelength laser exposures. The problem is first formulated and solved using standard mathematical programming techniques, and the results are compared to those from a simplified algorithm. The result is a method that can be efficiently integrated into existing laser modeling and hazard analysis software. As an example, overall visible light transmittance is maximized while maintaining eye-safe viewing conditions during a multiwavelength exposure, simultaneously minimizing the total optical density required for sufficient laser eye protection. This optimization formulation helps laser system users determine the proper laser eye protection for safe viewing in multiwavelength laser environments.

Background and Objectives In order to provide a direct comparison of the effects of mode-locked systems to those with continuous-wave (CW) or nonpulsed output, we have performed an experiment with lasers possessing otherwise identical output characteristics. This in vivo minimum visible lesion study compares retinal effects of mode-locked and CW lasers complete with histopathology of the treated areas. Study Design/Materials and Methods Titanium:Sapphire lasers produced 800-nm output for either mode-locked (76 MHz repetition rate, 120 femtoseconds) or CW exposures. Alternating CW and mode-locked laser exposures were delivered to the paramacular retinal region of rhesus subjects. Laser exposure duration was set to one-quarter second for both types of exposures. Through ophthalmoscopic examination of the fundus, a minimal visible lesion (MVL) threshold for damage was established. Results Approximately 75 test sites for each type of exposure were examined. The laser dosage thresholds and 95% confidence intervals for minimal visible damage at 24 hours postexposure were found to be 5.9 mJ (5.23–6.6 mJ) and 5.84 mJ (5.23–6.58 mJ) for mode-locked and CW exposures, respectively. Conclusions Results are compared with published studies conducted at similar exposures. These nearly identical damage thresholds indicate a primarily thermal tissue damage mechanism. Comparative histopathology of acute and chronic lesions of both exposure types is also presented. Lasers Surg. Med. 31:9–17, 2002. © 2002 Wiley-Liss, Inc.

Multiple-pulse lasers are routinely used in the laboratory for research, manufacturing, medical procedures, and in military applications. In order to provide a safe work environment for personnel using these lasers, safety standards have been established and have been in use for many years. These safety standards have addressed laser pulses of nanosecond duration and longer. Recently, safety standards have been updated to address laser pulses as short as 100 femtoseconds in duration. In order to tie these "ultrashort" laser pulses to hazard trends in currently established standards for multiple-pulse exposures with repetition rates less than several kilohertz, this experiment was conducted. Reported herein are minimum visible lesion thresholds in the paramacula of the primate retina using an 800-nm wavelength laser with 1,000 pulses per second, at 130 femtoseconds (fs) pulse duration. The minimum visible lesion (MVL) thresholds were determined at 1 h and 24 h post exposure for 1, 10, 100, 1,000, and 10,000 pulses and are compared with thresholds reported by other researchers. These new data are evaluated relative to the current safety standards for retinal exposure limits as a function of the number of pulses for femtosecond-pulse duration. Data from this study show that the retinal ED50 thresholds/pulse in the paramacula decrease by almost a factor of four as the number of pulses goes from one to ten and then decrease very little for an increase of three decades more in the number of pulses. The MVL-ED50 at the threshold decreased from 0.55 microJ for a single pulse to 0.15 microJ/pulse for 10 pulses and then only to 0.11 microJ/pulse for 10,000 pulses.

Over the past few years, a comprehensive rewrite of the American National Standard for Safe Use of Lasers (ANSI Z136.1) has been conducted. The ANSI Z136.1 is a user standard, as opposed to a manufacturer standard like the Federal Laser Product Performance Standard. As such, differing philosophies for hazard classification and application of safety control measures apply, based upon the user’s perspective. Here we present the second in a series of tutorial articles designed to clarify laser hazard analysis procedures under this new ANSI Standard. The procedure presented allows the reader to effectively determine the appropriate hazard classification for a small-source laser by using known laser output parameters in a step-by-step analysis.

The task of identifying explosives, hazardous chemicals, and biological materials from a safe distance is the subject we consider. Much of the prior work on stand-off spectroscopy using light has been devoted to generating a backward-propagating beam of light that can be used drive further spectroscopic processes. The discovery of random lasing and, more recently, random Raman lasing provide a mechanism for remotely generating copious amounts of chemically specific Raman scattered light. The bright nature of random Raman lasing renders directionality unnecessary, allowing for the detection and identification of chemicals from large distances in real time. In this article, the single-shot remote identification of chemicals at kilometer-scale distances is experimentally demonstrated using random Raman lasing.

Random lasers are a developing class of light sources that utilize a highly disordered gain medium as opposed to a conventional optical cavity. Although traditional random lasers often have a relatively broad emission spectrum, a random laser that utilizes vibration transitions via Raman scattering allows for an extremely narrow bandwidth, on the order of 10 cm−1. Here we demonstrate the first experimental evidence of lasing via a Raman interaction in a bulk three-dimensional random medium, with conversion efficiencies on the order of a few percent. Furthermore, Monte Carlo simulations are used to study the complex spatial and temporal dynamics of nonlinear processes in turbid media. In addition to providing a large signal, characteristic of the Raman medium, the random Raman laser offers us an entirely new tool for studying the dynamics of gain in a turbid medium., Unlike conventional lasers that require a uniform resonant cavity to operate, random lasers use a highly disordered gain medium in which scattering is dominant. Hokr et al. report Raman lasing from a bulk three-dimensional disordered medium whose intensity exceeds that of other random lasers by many orders of magnitude.

The time-temperature effects of laser radiation exposure are investigated as a function of wavelength. Here, we report the thermal response of bulk tissue as a function of wavelength from 700 to 1064 nm. Additionally, Monte Carlo simulations were used to verify the thermal response measured and predict damage thresholds based on the response.

An artificially pigmented retinal pigment epithelial (RPE) cell model was used to study the damage rates for exposure to 1, 10, 100, and 1,000 230-μs laser pulses at 532 nm, at two different concentrations of melanosome particles (MPs) per cell. Multiple pulses were delivered at pulse repetition rates of 50 and 99 pulses per second. Standard fluorescence viability indicator dyes and the method of microthermography were used to assess damage and thermal responses, respectively. Although frame rate during microthermography was more than five times slower than the duration of laser pulses, thermal information was useful in refining the BTEC computational model for simulating high-resolution thermal responses by the pigmented cells. When we temporally sampled the thermal model output at a rate similar to our microthermography, the resulting thermal profiles for multiple pulses resembled the thermal experimental profiles. Complementary to the thermal simulations, our computer-generated thresholds were in good agreement with the in vitro data. Findings are examined within the context of common exposure limit definitions in the national and international laser safety standards.

It has been shown that exposure of live neurons to a low-intensity pulsed infrared light can be used to excite action potentials. Infrared pulsed laser coupled to an optical fiber can be utilized to create a rapid localized increase in temperature in the vicinity of the cell. The resulting temperature gradient leads to an increase in membrane fluidity and permeability, causing depolarization of the target cell. In order to characterize the fluidity of the cell membrane at various temperatures with and without pulsed IR light exposure, we used a polarity-sensitive fluorescent probe di-4- ANEPPDHQ. This dye exhibits a fluorescent shift between the disordered and ordered phases of the membrane, and can be used to quantitatively evaluate the state of the membrane by calculating the generalized polarization (GP) value. Using high-speed imaging of cells exposed to a IR light of varying pulse width, it was determined that a longer pulse width leads to a greater change in the GP value. Comparison of GP values of cells at different ambient temperatures without the pulsed IR light exposure and cells exposed to pulsed IR light indicated that a rapid temperature gradient caused by the exposure to pulsed light induces a larger change in GP value than the ambient temperature increase alone, indicating a greater disruption of membrane fluidity and permeability.

Thresholds for microcavitation of isolated bovine and porcine melanosomes were determined using single nanosecond (ns) laser pulses in the NIR (1000 – 1319 nm) wavelength regime. Average fluence thresholds for microcavitation increased non-linearly with increasing wavelength. Average fluence thresholds were also measured for 10-ns pulses at 532 nm, and found to be comparable to visible ns pulse values published in previous reports. Fluence thresholds were used to calculate melanosome absorption coefficients, which decreased with increasing wavelength. This trend was found to be comparable to the decrease in retinal pigmented epithelial (RPE) layer absorption coefficients reported over the same wavelength region. Estimated corneal total intraocular energy (TIE) values were determined and compared to the current and proposed maximum permissible exposure (MPE) safe exposure levels. Results from this study support the proposed changes to the MPE levels.

The current national consensus standard for laser safety in the United States is the American National Standard for Safe Use of Lasers (ANSI Z136.1). Over the past few years, a comprehensive rewrite of this standard has been conducted. The updated version of the standard (Z136.1-2000) incorporates a wealth of new bioeffects data and establishes a number of new maximum permissible exposure (MPE) limits for laser safety. The updated standard also includes new procedures for the computation of MPE values, which must be understood by health physicists, laser safety officers, and others in the field of occupational safety. Here we present the first in a series of tutorial articles to clarify laser safety analysis procedures under this new standard. This article deals with the proper application of three rules for determining the appropriate MPE values for repetitively pulsed lasers or repeated exposures from laser beams.

Thresholds for microcavitation of bovine and porcine melanosomes were determined using nanosecond laser pulses in the near-infrared (1000 to 1319 nm) wavelength regime. Isolated melanosomes were irradiated by single pulses (10 or 50 ns) using a Q-switched Spectra Physics Nd:YAG laser coupled with an optical parametric oscillator (1000 to 1200 nm) or a continuum laser at 1319 nm. Time-resolved nanosecond strobe photography after the arrival of the irradiation beam allowed imaging of microcavitation events. Average fluence thresholds for microcavitation increased nonlinearly with increasing wavelength from ∼0.5 J/cm 2 at 1000 nm to 2.6 J/cm 2 at 1319 nm. Fluence thresholds were also measured for 10-ns pulses at 532 nm and found to be comparable to visible nanosecond pulse values published in previous reports. Calculated melanosome absorption coefficients decreased from 925 cm −1 at 1000 nm to 176 cm −1 at 1319 nm. This trend was found to be comparable to the decrease in retinal pigmented epithelial layer absorption coefficients reported over the same wavelength region. Estimated corneal total intraocular energy retinal damage threshold values were determined in order to compare to current and proposed maximum permissible exposure (MPE) safe levels. Results from this study support recently proposed changes to the MPE levels.

In recent years, several studies have been investigating the impact of thermal lensing in ocular media on the visual function. These studies have shown that when near-infrared (NIR) laser energy (1319 nm) is introduced to a human eye, the heating of the eye can be sufficient to alter the index of refraction of the media leading to transient changes in the visible wavefront through an effect known as thermal lensing, while remaining at a safe level. One of the main limitations of experimentation with human subjects, however, is the reliance on a subject’s description of the effect, which can vary greatly between individuals. Therefore, a computational model was needed that could accurately represent the changes of an image as a function of changes in the index of refraction. First, to model changes in the index of refraction throughout the eye, a computational thermal propagation model was used. These data were used to generate a comprehensive ray tracing model of the human eye using Zemax ( Radiant Zemax Inc, Redmond WA) via a gradient lens surface. Using this model, several different targets have been analyzed which made it possible to calculate real-world visual acuity so that the effect of changes in the index of refraction could be related back to changes in the image of a visual scene.

Reflections of high energy lasers from targets present safety challenges, as the resulting hazard distances can be significant. We have developed two different but complementary simulations to determine hazard zones resulting from high energy laser reflections. One, the High Energy Laser Collateral Assessment Tool (HELCAT), is a high-fidelity successor to the Laser Range Safety Tool (LRST), which had been developed specifically for distant targets. HELCAT has an improved user interface and uses first-principle physics calculations to obtain reflected irradiances at observer locations for each time step in a simulation. The time histories of the irradiances are used to determine the hazard zone. It supports a variety of simple and complex targets, trajectories, reflecting properties of materials, and observer locations. The other, termed the Specular Methodology, considers only specular reflections to derive analytical expressions for the irradiance and exposure time at observer locations. The hazard zone is derived from these values. While the Specular Methodology is an approximation of reflected laser light compared to HELCAT, it performs calculations much more rapidly. Therefore, we have been able to incorporate probabilistic techniques into the Specular Methodology, which provides additional information for risk assessment. Comparisons between the two simulations indicate acceptable agreement for equivalent scenarios.Reflections of high energy lasers from targets present safety challenges, as the resulting hazard distances can be significant. We have developed two different but complementary simulations to determine hazard zones resulting from high energy laser reflections. One, the High Energy Laser Collateral Assessment Tool (HELCAT), is a high-fidelity successor to the Laser Range Safety Tool (LRST), which had been developed specifically for distant targets. HELCAT has an improved user interface and uses first-principle physics calculations to obtain reflected irradiances at observer locations for each time step in a simulation. The time histories of the irradiances are used to determine the hazard zone. It supports a variety of simple and complex targets, trajectories, reflecting properties of materials, and observer locations. The other, termed the Specular Methodology, considers only specular reflections to derive analytical expressions for the irradiance and exposure time at observer locations. The hazard zone ...

Laser damage threshold energies produced from ultrashort (i.e., ⩽1 ns) laser pulses are investigated as a function of both pulse width and spot size for an artificial retina. A piece of film acts as the absorbing layer and is positioned at the focus of a variant on the Cain artificial eye [C. Cain, G. D. Noojin, D. X. Hammer, R. J. Thomas, and B. A. Rockwell, "Artificial eye for in vitro experiments of laser light interaction with aqueous media," J. Biomed. Opt.2, 88-94 (1997)]. Experiments were performed at the focal point and at two and ten Rayleigh ranges (RR) in front of the focus with the damage end point being the presence of a bubble imaged at the film plane. Pulse energy thresholds were determined for wavelengths of 1064, 580, and 532 nm with pulse durations ranging from the nanosecond (ns) to the femtosecond (fs) regime. For the at-focus data in the visible regime, the threshold dropped from 0.25 μJ for a 532 nm, 5 ns pulse to 0.11 μJ for a 580 nm, 100 fs pulse. The near-infrared (NIR) threshold changed from 5.5 μJ for a 5 ns pulse to 0.9 μJ for a 130 fs pulse at a distance two RR in front of the focus. The experiment was repeated using the same pulse widths and wavelengths, except the water path was removed to determine the impact of nonlinear self-focusing in water. A vertical microscope imaging system was employed in order to observe the threshold event. The NIR fluence threshold of 0.5 J/cm2 remained constant within an experimental uncertainty for all pulse widths, which corresponds to values in the literature [C. P. Lin and M. W. Kelly, "Ultrafast time-resolved imaging of stress transient and cavitation from short pulsed laser irradiated melanin particles," SPIE Laser-Tissue Interactions VI, Proc. SPIE2391, 294-299 (1995)]. The visible data also demonstrated a nearly constant fluence of 0.07 J/cm2. The disparity in thresholds between the two techniques arises from nonlinear optical phenomena related to propagation differences in the ocular fluid. © 1999 Society of Photo-Optical Instrumentation Engineers.

A new fiber-based imaging system has been incorporated into a modifie artificia eye for direct measurement of the thermal lensing effect induced by an infrared laser (1319 nm) to correlate changes in the visible wavefront to visual distortions observed by human subjects. The response of a visible beam, 632 nm, was observed with respect to various exposures of the infrared light under different power levels and exposure durations. Infrared irradiance levels between 0.57 and 4.56 W • cm -2 were used with exposure durations of 0.25, 0.50, 0.75, 1, and 2 seconds in order to observe the optimal level of radiant energy needed to bloom a visible beam at the retinal plane. Results show that deformation of the visible beam focused on the retina begins at irradiance levels of 2.28 W • cm -2 with significan blurring (10 times larger than the original size) at 3.80 W • cm -2 . A maximum visible beam size at the retina is achieved with exposure durations of 0.75 seconds, and no observable change was reported for longer exposure durations. These results strongly correlate to the previously determined threshold for visual distortion in human subjects using infrared lasers of 2.98 W • cm -2 . Based on these results, the visible wavefront will need to expand four times its original size in order to overcome any accommodation effects and induce an observable visual disruption in human subjects.