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A laser optoacoustic method for analyzing the effect of porosity on the local isotropic Young's modulus of composite materials was proposed and experimentally implemented. Using as an example samples of a metal matrix composite based on silumin with reinforcing microparticles of silicon carbide, SiC, in various concentrations, it is shown that to provide an effective increase in Young's modulus with increasing concentration of SiC, the porosity of the final sample should not exceed 2%. [ABSTRACT FROM AUTHOR]

To prepare the coherent population trapping (CPT) states with rubidium and cesium, the commonly used atoms in CPT studies, a coherent bi-chromatic light field with frequency difference of several GHz is a basic requirement. With a 200 MHz center frequency acousto-optic modulator (AOM), we have realized bi-chromatic laser fields with several GHz frequency splits through high diffraction orders. We have experimentally studied the coherence between two frequency components of a bi-chromatic laser beam, which is composed of ±6 orders with frequency split of 3 GHz diffracted from the same laser beam, and the measured residual phase noise is Δφ2<0.019 rad2. The bi-chromatic laser fields were used to prepare CPT states with 85Rb and 87Rb atoms, and high contrast CPT signals were obtained. For CPT states preparation, our study result shows that it is a feasible approach to generate the bi-chromatic light field with larger frequency splits through high diffraction orders of AOM. [ABSTRACT FROM AUTHOR]

We present an advanced high-resolution, compact laser lithography system for fast prototyping of complex integrated optics devices comprising microring resonators and photonic crystal structures. Precise and flexible structuring of photoresist patterns is achieved by combing three linear stages (xyz) for sample positioning and a two-dimensional acousto-optical deflector for laser beam steering and intensity control. A continuous wave diode laser operating at a wavelength of 375 nm is used to illuminate all types of photoresists including SU-8. Using a microscope objective with a numerical aperture of 1.40, structure widths of ∼200 nm can be obtained. The write-field covered by acousto-optic deflection can be as large as 200×200 μm2 when using an objective with a focal length of 4.5 mm. With a two-step lithography process, gaps as small as 150 nm between adjacent structures have been achieved, yielding superior photoresist masks for microring resonators with coupling ports. [ABSTRACT FROM AUTHOR]

The developments in the area of lasers and photonics opened new applications in biology and biotechnology. Solid state lasers can create highly localized traps at its depth of focus using specially designed beam expansion and focusing optics. In the present investigation, we report the design and development of an arc lamp pumped Nd:YAG laser operating at 1064nm with high beam quality for optical tweezers applications. The laser sources can be operated at lower power levels up to 2W and with high beam quality (M² factor) for optical tweezers applications. Such laser tweezers can be used effectively for studying the interaction force between arterial cells and implant surfaces and also in the study of cellular and drug biomechanism. The mode limiting aperture is restricting higher order modes and therefore in TEM00 mode also, the slope efficiency decreases more. The beam quality should be high for creating a better optical trap for microscopic objects and hence use of mode limiting apertures are highly necessary in the present optical resonator configuration. [ABSTRACT FROM AUTHOR]

An efficient singly resonant intracavity optical parametric oscillator (OPO) is demonstrated based on a type II non-critically phase-matched KTiOAsO4 (KTA) crystal. A diode-end-pumped acousto-optically (AO) Q-switched Nd:YAG laser is used as the pumping source. Under a LD power of 7.43 W and a pulse repetition rate of 15 kHz, we obtain a signal power of 0.93 W, corresponding to an optical-to-optical conversion efficiency of 12.5%. This is the highest efficiency reported for the intracavity KTA OPOs. Theoretical analysis on the power characteristics of the OPO is performed. It is proved from the theoretical results that the reflectivity of 63% at the signal wavelength (1535 nm) is a good selection for high average power and high conversion efficiency. [ABSTRACT FROM AUTHOR]

A high-power high-repetition-rate acousto-optically Q-switched 1342 nm laser with double Nd:YVO4 crystals pumped by fiber-coupled laser diodes is presented. The highest output power of 13.7 W was achieved with a total of 42 W pumping power in cw operation, the slope efficiency was measured as 36%, and the optical efficiency was better than 32%. In Q-switchedoperation, the highest pulse repetition rate of 100 kHz was obtained. At 50 kHz repetition rate, the laser exported 11.2 W average output power, with 60 ns average pulse width, ∼5% width stability (RMS) and ∼8% peak-power stability (RMS). At 10 kHz repetition rate, the highest average output power was measured as 6.3 W, single pulse energy was calculated as 0.63 mJ, with pulse width of 19 ns and peak-power higher than 30 kW. Combining the experimental results, we analyze and discuss some problems concerning Nd:YVO4 crystal working at 1,342 nm wavelength. [ABSTRACT FROM AUTHOR]

Abstract: We describe the hardware and software of the high-sensitive two-channel opto-acoustic spectrometer with a near infrared diode laser. A semiconductor TEC-100 laser with outer resonator generates a continuous single-frequency radiation in the range of 6040–6300cm−1 with spectral resolution better that 10MHz. The newly designed model of photo-acoustic cells in the form of a ring type resonator was used in the spectrometer, and the system allows the measurement of a weak absorption coefficient equal to 1.4×10−7 cm−1 Hz−1/2 with a laser radiation power of 0.003W. The methane absorption spectra within a range of 6080–6180cm−1 were measured with a spectral resolution of 10MHz and the signal to noise ratio more than 103. Six hundred absorption lines were recorded, which is twice as many as in HITRAN-2004. The accurate measurements of the half-width and shift of methane unresolved triplet R3 of 2ν 3 band permit us to determine values of the broadening and shift coefficients for CH4–air, CH4–N2, and CH4–SF6 mixtures. [Copyright &y& Elsevier]

Three photoacoustic (PA) cells designed for trace-gas sensing were compared by measuring absorption by the P(15) rotational line of the $\upsilon_{1}+\upsilon_{3}$ vibrational combination band of acetylene using a distributed-feedback diode laser. Normalised sensitivities were determined for each cell by analysis of the signal to noise ratios of acquired spectra. The first cell was constructed in-house, and contained a single electret microphone held in a stainless steel tube. The second cell was a differential PA cell that contained two microphones housed in identical flow tubes, with one microphone to detect the PA signal and the other to determine background noise levels. The third cell contained a novel cantilever pressure sensor, movement of which was measured by a compact laser interferometer. Normalised sensitivities (2σ) of 3.1×10-7, 1.7×10-7 and 2.2×10-9 cm-1 W Hz-1/2, respectively, were obtained. An erbium-doped fibre amplifier was used to amplify the laser power, and a detection limit of 9.8×1010 molecule cm-3 was obtained using the cantilever pressure sensor PA cell, with a laser power of 1.17 W. This detection limit corresponded to a mixing ratio of 14.5 parts per billion by volume at 277 mbar. [ABSTRACT FROM AUTHOR]

An acousto-optic laser deflector was used to image the intensity distribution of a continuous wave laser of microsecond order. Undeflected light was blocked while the deflected light was directed to a CCD camera, which allowed imaging of the incident laser intensity distribution of microsecond order. Experiments using a test pattern showed that there was no distortion in the deflected image. The resolution limit, estimated from diffractive effects, was about 0.2 mrad. Using this method of high-speed imaging, density variations accompanying laser-induced breakdown in air were visualized by shadowgraphy and interferometry. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 55–61, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20386 [ABSTRACT FROM AUTHOR]

An acoustooptic tunable filter (AOTF) is used to detect multiple fluorescent signals on a fluidic microdevice. A confocal laser-induced fluorescence detection setup is used to excite fluorescent dyes in glass microchannels, presenting a streamlined and robust detection system consisting of the narrow-bandwidth AO filter and a single photodetector. The flexibility of the filter is demonstrated by alternating between wavelengths for precise microchannel alignment and sweeping through a range of wavelengths for preliminary spectral characterization of subnanoliter probe volumes of target analytes. The AOTF is also coupled with an electrophoretic separation for the multicolor detection of PCR-amplified DNA against a labeled sizing standard, the discrimination of multiple amplicons overlapped in time, and the identification of amplified biowarfare agents in a fluorescent spiking experiment. Finally, to demonstrate the multicolor capability of the system, 19-wavelength detection is performed during the separation of a three-dye sample mixture. [ABSTRACT FROM AUTHOR]

We have developed a new Brewster-cut acousto-optic programmable gain control filter to optimize the spectral losses inside a regenerative cavity. This spectral amplitude control combined with an acousto-optic programmable dispersive filter for the spectral phase control optimizes, in a few steps of a direct algorithm, the performance of a 10-Hz CPA Ti:sapphire laser to 18-fs pulse duration, 1.2% RMS energy stability and 107 contrast ratio. [ABSTRACT FROM AUTHOR]

An acousto-optic laser deflector was used for visualization of high-speed phenomena, such as shock waves and density perturbations accompanying an impulse discharge, or shock waves generated by laser-induced breakdown in air. Using a continuous wave laser as the light source, shadowgraphs of shock waves and density perturbations were obtained at shutter speeds down to 1µs. Results showed that shock waves propagated at a speed of 417 m/s in the case of an impulse discharge, and 485 m/s in the case of laser-induced breakdown. Prebreakdown phenomena such as leaders progressing from the high-voltage electrode were also visualized. Compared to conventional high-speed imaging techniques, this method is useful when using a laser light source, since the acousto-optic crystal can accommodate high-intensity laser light. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 9–15, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20279 [ABSTRACT FROM AUTHOR]

Fourier-transform-limited pulses of programmable length and shape have been generated in the range λ=720–825 nm from the continuous-wave output of a Ti3+-doped sapphire (Ti:Sa) ring laser using a pulsed acousto-optic modulator (AOM). The minimal rise time of the pulses amounts to 10 ns and is limited by the size of the cw laser beam in the active medium of the AOM. Amplification of the radiation pulses in Nd:YAG-pumped Ti:Sa crystals into intense pulses of near-infrared (NIR) radiation with pulse energies of up to 15 mJ was demonstrated at a repetition rate of 25 Hz. Frequency upconversion into the ultraviolet (UV) by frequency doubling (νUV=2νNIR) or by mixing the fundamental NIR radiation with the doubled radiation (νUV=3νNIR) in nonlinear crystals was achieved under conditions where the pulse shapes could be preserved. The pulse energies amounted to up to 1 mJ for the doubled radiation and 100 μJ for the tripled radiation for NIR pulses of 30 ns duration. Vacuum ultraviolet (VUV) radiation pulses of 108–109 photons/pulse at 120 000 cm-1 were generated by two-photon resonance-enhanced third-harmonic generation in a pulsed gas beam of xenon. The VUV pulse length could be adjusted between 10 and 20 ns, and double pulses of VUV radiation separated by a variable delay of up to 100 ns could be generated. Frequency chirps arising in the AOM and the pulsed amplification were found to be negligible, but a frequency shift of -5 MHz was determined. The bandwidth of the generated radiation was estimated to be 35 MHz in the UV at a wave number of ≈40 000 cm-1 and 55 MHz in the VUV at a wave number of ≈120 000 cm-1 in a Doppler-free measurement of the (5p)6 1S0→(5p)56p[1/2](J=0) two-photon resonance of xenon. The absolute accuracy of the wave-number calibration is limited by uncertainties in the positions of NIR lines of I2 taken as reference standard. [ABSTRACT FROM AUTHOR]

We demonstrate a compact efficient diode-pumped acousto-optically Q-switched intracavity-frequency-tripled Nd:YVO4 blue laser. The optimum polarization state is experimentally investigated to optimize the output performance. Greater than 280 mW of 447-nm average power at a repetition rate of 25 kHz was generated with a 15-W diode pump power. At 25 kHz, the pulse width is shorter than 15 ns and the peak power is higher than 800 W. [ABSTRACT FROM AUTHOR]

An original combination of two cascaded acousto-optic modulators and electro-optic polarization commutators for stereoscopic laser videoprojection is presented. It is based on the separation by orthogonal polarizations of the two left and right images of a stereoscopic pair. As four lines are scanned simultaneously, a quadrifrequency paratellurite acousto-optic modulator is detailed. The electro-optic cell acts like a commutator switching the polarization from the left state polarization state to the right one. This new architecture is then described and experimentally validated. [ABSTRACT FROM AUTHOR]

In this letter, we report on an alternative method to fabricate a high-efficiency planar-type oxide-confined 850-nm vertical-cavity surface-emitting lasers (VCSELs). The planarized process of VCSELs was to use the silicon oxide as the buried layer. As a result, these devices with an oxidized aperture of 3 pm in diameter exhibit a single-transverse mode behavior throughout the operation current range. In addition, the static characteristics of VCSELs at 300 K include a threshold current of 0.52 mA corresponding to a threshold voltage of 2.2 V, a maximum single transverse-mode light output power of 1.13 mW at 4.5 mA, and an external differential quantum efficiency of 35%. On the other hand, this TO-packaged planar-type 850-nm VCSEL for back-to-back test shows a wide open along with symmetric eye diagram and could also pass the 10 Gb/s mask as operating at 10.3 Gb/s and 4 mA. Furthermore, the VCSEL can still keep the eye diagram open and symmetric after the 66-m multi-mode fiber transmission and has a power penalty of 6.6 dB because of fiber dispersion for 10.3 Gb/s data rate at a bit error rate of 10-11. These results confirm the excellent high-speed performance of SiOx-planarized VCSELs as compared to the polyimide-planarized VCSELs. [ABSTRACT FROM AUTHOR]

A novel Q-switching approach, using both an acoustooptic (AO) Q-switch and an un-coated GaAs saturable absorber, is demonstrated in a diode end-pumped Nd:YVO4 laser. The simultaneous use of passive and active Q-switching can generate short pulses with high peak powers and symmetric temporal profiles. A peak power of 25 kW has been achieved in laser pulses with width of 3 ns at 1 kHz. [Copyright &y& Elsevier]

This paper deals with a laser-cleaning process for removing a layer of paint. The effects of each individual laser pulse were monitored by a three-probe system. Ultrasonic signals from the rear surface of the substrate were obtained using an arm compensated Michelson interferometer, the optoacoustic waves in the surrounding air were detected using a laser beam deflection probe and the shape of the growing crater was measured using a laser anamorph profilometer. Two different cleaning lasers were used: an Excimer and a Nd:YAG laser. Typical parameters of the optodynamic signals versus the laser-pulse number are presented. A linear correlation between the quantity of ablated material and the integral of the ultrasonic signals was found together with an exponential relationship between the time-of-flight of the optoacoustic signals and the decoating rate. [Copyright &y& Elsevier]

The preparation of the use of resin-bonded superabrasive grinding wheels remains a problem despite their availabilities on the market in the past years and possible technological advantages. In this paper, an acousto-optic Q-switched Nd:YAG pulsed laser is applied to dressing resin-bonded superabrasive wheels in orthogonal direction. The author proposes a systematical study on the mechanism of selective removal, crater ablated by single pulse and surface topography after dressing, and consequently presents a feasible method of selecting irradiation parameters and summarizes the dressing features and disciplines of dressing effects influenced by these parameters. Experiments results indicate the surface topography dressed by acousto-optic Q-switched YAG pulsed laser dressing is much superior to mechanical dressing and CW laser dressing. [Copyright &y& Elsevier]

The possibility of using a semiconductor crystal simultaneously as an element of nonlinear negative feedback and as a saturable absorber was studied. Numerical computer simulation of a laser model was performed. The calculations were carried out for a GaAs crystal. Analysis of the results showed that, at a corresponding concentration of defect levels and crystal thickness, it is possible to realize both nonlinear negative feedback and saturable absorption in the same crystal for mode locking. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

This article describes an automatic system that permanently keeps an extended cavity diode laser (ECDL) frequency locked to a cesium line (852 nm). The ECDL has a new architecture based on an intracavity étalon. The laser power is 30 mW and the linewidth is narrower than 50 kHz. Two acousto-optic modulators finely change the laser frequency and optical power. The electronic control is composed of a computer, microcontrollers, digital analog converters, and direct digital synthesizers. The computer searches the ECDL parameters to tune it to the Cs line and closes the servoloop. It permanently checks the servoloop and relocks the laser if necessary. Both acousto-optic modulators are driven in real time by microcontrollers. They are programed in order to control the laser power and frequency with a predefined time sequence. This system, especially developed for an atomic fountain, can be easily adapted to a wide range of applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The output pulse parameters of a mode-locked Nd:YAG laser with a passive negative feedback element were studied experimentally. The pulse evolution within the train was experimentally recorded using a modified second harmonic generation autocorrelator. By comparing the laser operation with and without an acousto-optic modulator, we found that with the later there is a significant increase in the mode locking probability and the pulse acquires a temporally Gaussian symmetric pulse shape. Further with the active modulator there is a relaxation in alignment tolerances and increase in the range of permissible dye concentrations for stable mode locking. It was also observed that the pulse width of the negative feedback laser depends on the saturation intensity of the mode locking dye and reduces for a dye with higher saturation intensity. The pulse width was also found to reduce linearly as the initial transmission of the dye is reduced. [Copyright &y& Elsevier]

The dependence of nonreciprocal behavior of AO device on ultrasonic wave signals was investigated by means of Bragg diffraction equation. The result showed that through choosing suitable ultrasonic frequencies input to AO device, unidirectional operation in ring laser could be achieved without mechanical rotation. Furthermore, the use of narrowband AO device, acousto-optic tunable filter (AOTF) as a unidirectional operation element for the ring cavity laser was investigated in theory and experiment. The result showed that it could induce a high loss difference for the counter-rotating beams, while keeping the low diffraction loss at an appropriate radio frequency. This indicates that AOTF is attractive for use as an optical diode for unidirectional operation in ring cavity lasers. [Copyright &y& Elsevier]

Presents information on a study which developed an acoustic-optic Q-switched Cr-Tm:YAG laser. Methodology of the study; Results and discussion.

A new scheme for locking an acoustic resonance of an acousto-optic modulator to the exciting rf field applied for laser mode locking is presented. The resonance of the mode-locking quartz prism is temperature-tuned to match the synthesizer frequency. Deviation from perfect matching is sensed by observing the relative phase of the rf wave reflected at the device, and the error signal is fed back by a servo loop adjusting the heat delivered by a heating transistor to maintain the temperature required for exact resonance. The performance of the resonance-tracking loop was checked on several different resonances of the modulator (used in an argon-ion laser), because switching to another resonance is a simple and attractive way for changing the laser pulse repetition rate (or mode spacing) without replacing the mode-locker unit. Excellent loop response was found in all cases. The new tracking principle provides a widely extended tracking range, improved tracking accuracy and laser stability, and simplifies the laser adjustment. [ABSTRACT FROM AUTHOR]

A low-pressure optoacoustic cell is described that can be used to lock the emission frequency of a laser. A model is developed which describes the low-pressure behavior of the optoacoustic cell as a function of cell dimensions, gas properties, and operating pressure. Resonant optoacoustic cells are predicted to improve the acoustic signal levels significantly. Experiments were carried out with a cell filled with CF4. The model was found to accurately predict resonator quality, resonance frequency, and acoustic response for pressures ranging from 0.1 to 3.0 kPa. At these low pressures acoustic attenuation processes, slow vibration to translation (VT) relaxation and diffusion to the cell wall strongly influence the acoustic behavior of the cell. Using the relaxation time of the ν4 vibrational mode of CF4 as a fitting parameter its value was determined to be three times slower than VT relaxation from the ν2 level. The experimental values for the response were predicted by the model with an error of less than 10% in the whole pressure range. Predictions for the optoacoustic signal for different resonator dimensions were also confirmed. Model predictions for the optoacoustic signal for mixtures of gases and the influence of the temperature are also given. Especially the option of cooling the gas seems to be attractive for the case of CF4. [ABSTRACT FROM AUTHOR]

A high resolution full color printer has been developed incorporating a He-Cd+ white-light laser, acousto-optic modulators, a Galvano scanner, and a circular arc recording platen on a fine translation stage. The laser oscillates at three primary colors and is controlled to be within 1% intensity stability. The spot size of the laser beam on the recording platen is improved to be 50 μm in diameter while the positioning accuracy for both horizontal and vertical scans are achieved to be better than 25 μm. The exposing energy densities on the recording surface for red, green, and blue are measured to be 4.3, 8.4, and 8.4 erg/cm2, respectively. The energy densities exceed the required exposure energy for Polacolor ER 8×10 Land film. A ‘‘reversible coding method’’ has been applied to shorten the data process time for 153.6 Mbytes image data. As the result, a 250×200 mm2 color print can be produced in 2 min. To evaluate chromaticity of the color prints, a color estimator that consists of a colorimeter, a personal computer, and an XY plotter is developed. The purity of color is found out to be high because of color matching between the laser wavelengths and the spectral sensitivity of the film. [ABSTRACT FROM AUTHOR]

We experimentally realized a planar acoustic superlens by a simple structure consisting of periodically arrayed rigid slabs. Based on the excitation of guided modes and the moderate amplification of the evanescent waves, we have broken the diffraction limit and obtained a subwavelength image with a half-power beamwidth of 0.07λ. All the experimental results are in good agreement with the theoretical simulations via finite difference time domain method. [ABSTRACT FROM AUTHOR]

A high-power continuous-wave (CW) laser-diode (LD) pumped acousto-optic Q-switched Nd:YVO4 laser is presented. A short pulse at 1064 nm is obtained. With a repetition rate of 50 kHz, a maximum average output power of 5.72 W is achieved. The optical-conversion efficiency and the slope efficiency are 28% and 32.4%, respectively. At the repetition rate of 10 kHz and the pulse width of 16.3 ns, the maximum single-pulse energy of 286 μJ and the peak power of 13 kW are acquired. The laser can be used as a signal source for free-space optical communication. The output signal agrees well with the modulate signal. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 281–283, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20278 [ABSTRACT FROM AUTHOR]

Active, passive, and active–passive mode locking of the iodine photodissociation laser are investigated. The peak-to-background ratio (PBR) of the acousto-optically mode-locked pulse is 85% for rf power of 5 W. Passive mode locking using BDN dye gives PBR of 75% and has inferior reproducibility. The active–passive mode locking using the two methods simultaneously is useful for the pressure broadened iodine laser line and gives a PBR of 91%. In this case the rf power required for complete mode locking is calculated to be 7 W which is much less than the required power of 11 W in using active mode locking alone. [ABSTRACT FROM AUTHOR]

The article offers information about laser optoacoustic imaging. It is stated that laser optoacoustic imaging is a promising and non-invasive technique for cancer detection. The method works by firing short laser pulses at the area to be visualized. In addition, tissue absorbs the light and rapidly increases in temperature and generates expansion shock waves.

A simultaneous Q-switched and mode-locked (QML) Nd:LuVO4 laser with an acousto-optic (AO) modulator and GaAs was presented. By inserting an AO modulator into the laser cavity, the stability of the QML pulses was improved and the pulse width was compressed significantly. The pulse energy and the peak power of mode-locked pulses under the Q-switched envelope had greatly increased. Considering the influences of the turnoff time and the modulation frequency of the AO modulator, a rate equation model for dual-loss modulated QML lasers was given and the numerical solutions of the rate equations were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]