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Highlights: Based on Fe-Hpdca-PDMS and carbon nanotube composite, an optoacoustic patch is developed, which can recover from the damage induced by cutting or laser irradiation at room temperature. The patch has high laser damage threshold (183.44 mJ cm−2) and optoacoustic energy conversion efficiency (10.66×10−3). The patch has been successfully examined in acoustic flow, thrombolysis, and wireless energy harvesting, which may provide new insights into the field of the design and fabrication of novel ultrasound devices for biomedical applications. Compared with traditional piezoelectric ultrasonic devices, optoacoustic devices have unique advantages such as a simple preparation process, anti-electromagnetic interference, and wireless long-distance power supply. However, current optoacoustic devices remain limited due to a low damage threshold and energy conversion efficiency, which seriously hinder their widespread applications. In this study, using a self-healing polydimethylsiloxane (PDMS, Fe-Hpdca-PDMS) and carbon nanotube composite, a flexible optoacoustic patch is developed, which possesses the self-healing capability at room temperature, and can even recover from damage induced by cutting or laser irradiation. Moreover, this patch can generate high-intensity ultrasound (> 25 MPa) without the focusing structure. The laser damage threshold is greater than 183.44 mJ cm−2, and the optoacoustic energy conversion efficiency reaches a major achievement at 10.66 × 10−3, compared with other carbon-based nanomaterials and PDMS composites. This patch is also been successfully examined in the application of acoustic flow, thrombolysis, and wireless energy harvesting. All findings in this study provides new insight into designing and fabricating of novel ultrasound devices for biomedical applications. [ABSTRACT FROM AUTHOR]

Miniaturized sound generators are attractive to realize intriguing functions. Thermoacoustic device's application is seriously limited due to the frequency‐doubling phenomenon. To address this issue, photoacoustic sound generator is considered as a promising alternative. Here, based on vertical single‐wall carbon nanotubes (CNTs) array, we introduce a photoacoustic sound generator with internal nano‐Helmholtz cavity. Different from traditional device that generates sound by periodically heating up the open space air around material, this sound generator produces an audio signal by forming a forced vibration of the air inside the CNTs. Interestingly, anomalous photoacoustic behavior is observed that the sound pressure level (SPL) curve has a resonance peak, the corresponding frequency of which is inversely proportional to the CNTs array's height. Furthermore, the energy conversion efficiency of this photoacoustic device is 1.64 times as large as that of a graphene sponge‐based photoacoustic device. Most importantly, this device can be employed for music playing, bringing a new clew for the development of musical instruments in the future. [ABSTRACT FROM AUTHOR]

Nonlinear oscillations in micro- and nanoelectromechanical systems have emerged as an exciting research area in recent years due to their promise in realizing low-power, scalable, and reconfigurable mechanical memory and logic devices. Here, we report ultralow-power mechanical memory operations utilizing the nonlinear oscillation regime of GaN microcantilevers with embedded piezotransistive AlGaN/GaN heterostructure field effect transistors as highly sensitive deflection transducers. Switching between the high and low oscillatory states of the nonlinear oscillation regime was demonstrated using a novel phase-controlled opto-mechanical excitation setup, utilizing a piezo actuator and a pulsed laser as the primary and secondary excitation sources, respectively. Laser-based photoacoustic excitation was amplified through plasmonic absorption in Au nanoparticles deposited on a transistor. Thus, the minimum switching energy required for reliable memory operations was reduced to less than a picojoule (pJ), which translates to one of the lowest ever reported, when normalized for mass. [ABSTRACT FROM AUTHOR]

Fiber laser technology has experienced a rapid growth over the past decade owing to increased applications in precision measurement and optical testing, medical care, and industrial applications, including laser welding, cleaning, and manufacturing. A fiber laser can output laser pulses with high energy, a high repetition rate, a controllable wavelength, low noise, and good beam quality, making it applicable in photoacoustic imaging. Herein, recent developments in fiber-laser-based photoacoustic microscopy (PAM) are reviewed. Multispectral PAM can be used to image oxygen saturation or lipid-rich biological tissues by applying a Q-switched fiber laser, a stimulated Raman scattering-based laser source, or a fiber-based supercontinuum source for photoacoustic excitation. PAM can also incorporate a single-mode fiber laser cavity as a high-sensitivity ultrasound sensor by measuring the acoustically induced lasing-frequency shift. Because of their small size and high flexibility, compact head-mounted, wearable, or hand-held imaging modalities and better photoacoustic endoscopes can be enabled using fiber-laser-based PAM. [ABSTRACT FROM AUTHOR]

Optoacoustic imaging is a new biomedical imaging technology with clear benefits over traditional optical imaging and ultrasound. While the imaging technology has improved since its initial development, the creation of dedicated contrast agents for optoacoustic imaging has been stagnant. Current exploration of contrast agents has been limited to standard commercial dyes that have already been established in optical imaging applications. While some of these compounds have demonstrated utility in optoacoustic imaging, they are far from optimal and there is a need for contrast agents with tailored optoacoustic properties. The synthesis, encapsulation within tumor targeting silica nanoparticles and applications in in vivo tumor imaging of optoacoustic contrast agents are reported. [ABSTRACT FROM AUTHOR]

Image performance in optoacoustic endoscopy depends markedly on the design of the transducer employed. Ideally, high-resolution performance is required over an expanded depth of focus. Current optoacoustic focused transducers achieve lateral resolutions in the range of tens of microns in the mesoscopic regime, but their depth of focus is limited to hundreds of microns by the nature of their spherical geometry. We designed an ultra-broadband axicon detector with a 2 mm central aperture and investigated whether the imaging characteristics exceeded those of a spherical detector of similar size. We show a previously undocumented ability to achieve a broadband elongated pencil-beam optoacoustic sensitivity with an axicon detection geometry, providing approximately 40 μm-lateral resolution maintained over a depth of focus of 950 μm—3.8 times that of the reference spherical detector. This performance could potentially lead to optoacoustic endoscopes that can visualize optical absorption deeper and with higher resolution than any other optical endoscope today. [ABSTRACT FROM AUTHOR]

Self-assembled Fe3O4 nanoparticles are attracting more and more interests in biomedical field, such as dual photoacoustic devices and magnetic resonance imaging. At present, however, the preparation of self-assembled Fe3O4 nanoparticles mainly relies on the modifications of some toxic polymers, such as 4-vinylpyridine, polyacrylonitrile, and phenol formaldehyde resin. Additionally, the synthetic methods used were too complicated. The biological toxicity and complex methods significantly limit the biomedical applications of self-assembled Fe3O4 nanoparticles. In this work, natural polysaccharide chitosan was used to modify Fe3O4 nanoparticles. The self-assembled Fe3O4 nanochains were obtained easily by controlling the ratio of chitosan and Fe3O4 nanoparticles. The formation mechanism of Fe3O4 nanochains was proposed and demonstrated by experiments and numerical simulation. It is found that the thickness of chitosan is a key factor that affects the magnetic field distributions and magnetic attraction of Fe3O4 nanoparticles. The prepared chitosan-modified Fe3O4 nanochains would be a promising candidate with good biocompatibility for biomedical applications. [ABSTRACT FROM AUTHOR]

Photoacoustics is a promising technique for in-depth imaging of biological tissues. However, the lateral resolution of photoacoustic imaging is limited by size of the optical excitation spot, and therefore by light diffraction and scattering. Several super-resolution approaches, among which methods based on localization of labels and particles, have been suggested, presenting promising but limited solutions. This work demonstrates a novel concept for extended-resolution imaging based on separation and localization of multiple sub-pixel absorbers, each characterized by a distinct acoustic response. Sparse autoencoder algorithm is used to blindly decompose the acoustic signal into its various sources and resolve sub-pixel features. This method can be used independently or as a combination with other super-resolution techniques to gain further resolution enhancement and may also be extended to other imaging schemes. In this paper, the general idea is presented in details and experimentally demonstrated. [ABSTRACT FROM AUTHOR]

Elasticity is one basic property of hybrid organic-inorganic perovskites. It highly relates to many fundamental processes in solid physics. The investigation of elasticity is of interest not only to explore the intrinsic properties of a material, but also to improve their potential application performance. In this study, we predict photoacoustic eigen-spectrum (PAES) of single crystal. Then by solving the inverse problem of the generation of PAES, we propose a noncontact method to determine a complete set of elastic constants of single crystal in one test. Experiments confirm the proposed method accurately determines all elastic constants of MAPbBr3. Since this method is totally noncontact and does not require multiple specimens cutting along different crystal axes, it could be more competent for rare, tiny and brittle specimen, or when the specimen is immersed in turbid or opaque medium. Benefitting from these superiorities, the proposed method might be found prominent values in materials science and applications. [ABSTRACT FROM AUTHOR]

Photoacoustic endoscopy (PAE) is a method of in-vivo imaging that uses tissue absorption properties. In PAE, the main tools used to detect the acoustic signal are mechanical ultrasound transducers, which require direct contact and which are difficult to miniaturize. All-optic photoacoustic sensors can challenge this issue as they can provide contact-free sensing. Here, we demonstrate sensing of photo-acoustic signals through a multimode fiber (MMF) which can provide an ultra-thin endoscopic photoacoustic sensor. Furthermore, we show the advantage of using the optical-flow method for speckle sensing and extract the photoacoustic signal despite the mode-mixing along the MMF. Moreover, it is demonstrated for the first time that the speckle reconstruction method can be used without the need for imaging of the speckles as this enables the use of multimode fibers for the speckle method. [ABSTRACT FROM AUTHOR]

Most imaging studies of immunotherapy have focused on tracking labeled T cell biodistribution in vivo for understanding trafficking and homing parameters and predicting therapeutic efficacy by the presence of transferred T cells at or in the tumour mass. Conversely, we investigate here a novel concept for longitudinally elucidating anatomical and pathophysiological changes of solid tumours after adoptive T cell transfer in a preclinical set up, using previously unexplored in-tandem macroscopic and mesoscopic optoacoustic (photoacoustic) imaging. We show non-invasive in vivo observations of vessel collapse during tumour rejection across entire tumours and observe for the first time longitudinal tumour rejection in a label-free manner based on optical absorption changes in the tumour mass due to cellular decline. We complement these observations with high resolution episcopic fluorescence imaging of T cell biodistribution using optimized T cell labeling based on two near-infrared dyes targeting the cell membrane and the cytoplasm. We discuss how optoacoustic macroscopy and mesoscopy offer unique contrast and immunotherapy insights, allowing label-free and longitudinal observations of tumour therapy. The results demonstrate optoacoustic imaging as an invaluable tool in understanding and optimizing T cell therapy. [ABSTRACT FROM AUTHOR]

A benchmark experiment is reported that demonstrates the shortening of hard X‐ray pulses in a synchrotron‐based optical pump–X‐ray probe measurement. The pulse‐shortening device is a photoacoustic Bragg switch that reduces the temporal resolution of an incident X‐ray pulse to approximately 7.5 ps. The Bragg switch is employed to monitor propagating sound waves in nanometer thin epitaxial films. From the experimental data, the pulse duration, diffraction efficiency and switching contrast of the device can be inferred. A detailed efficiency analysis shows that the switch can deliver up to 109 photons s−1 in high‐repetition‐rate synchrotron experiments. [ABSTRACT FROM AUTHOR]

Bragg diffraction which provides effective acoustooptic interaction of three-color radiation with a single acoustic wave at a high frequency of sound is proposed and tested in a single crystal of paratellurite at the wavelengths of λ= 0.488, 0.514, and 0.633 μm. Maximal diffraction efficiency of radiation with λ=0.633 μm at acoustic frequency of 150 MHz is 88% and that with λ= 0.488 μm and λ=0.514 μm is 60%. In diffraction efficiency range from 0 to 40% the dependence of all beams on acoustic power is the same. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging using a focused, scanning detector in combination with a pulsed light source is a common technique to visualize light-absorbing structures in biological tissue. In the acoustic resolution mode, where the imaging resolution is given by the properties of the transducer, there are various challenges related to the choice of sensors and the optimization of the illumination. These are addressed by linking a Monte Carlo simulation of energy deposition to a time-domain model of acoustic propagation and detection. In this model, the spatial and electrical impulse responses of the focused transducer are combined with a model of acoustic attenuation in a single response matrix, which is used to calculate detector signals from a volumetric distribution of absorbed energy density. Using the radial symmetry of the detector, the calculation yields a single signal in less than a second on a standard personal computer. Various simulation results are shown, comparing different illumination geometries and demonstrating spectral imaging. Finally, simulation results and experimental images of an optically characterized phantom are compared, validating the accuracy of the model. The proposed method will facilitate the design of photoacoustic imaging devices and will be used as an accurate forward model for iterative reconstruction techniques. [ABSTRACT FROM AUTHOR]

We have studied the features of noncollinear acousto-optic filtering of quasi-nondiffracting Bessel light beams in uniaxial crystals. We have obtained coupled wave equations for the vector amplitudes of an incident ordinary (o-type) Bessel beam and an extraordinary (e-type) diffracted beam for different modes. We have found an expression for the diffraction efficiency as a function of the parameters of interacting ordinary and extraordinary Bessel beams, and also as a function of the values of the overlap integrals. Using the overlap integral method, we have shown that regardless of the mode order for the Bessel light beam, under transverse phase matching conditions for ordinary and extraordinary diffracted Bessel beams in the optical spectral range 0.4-1.1 μm we can achieve a filter transmission bandwidth of ~0.6 nm in paratellurite crystals. [ABSTRACT FROM AUTHOR]

This study reports the application of an optoacoustic method for evaluating the bonding strength of ultrasonically bonded joints in a non-destructive and non-contact fashion. It is proposed that the bonding strength is correlated with the resonant frequency of bonded joints. The bonding strength measured with a destructive tensile test roughly increased with the vibration time, however, it varied, causing the transitional and dispersed formation of micro-bonds at the bonding interface. Scanning Electron Microscopic observation of the fractured surface suggested that the bonding strength depends on the total bonded area of micro-bonds. Frequency response of the bonded joint was examined with a non-destructive method using a piezo-electric vibrator. The experiment revealed that the resonant frequency exponentially increased with the bonding strength. In addition, this vibration behavior was dynamically visualized with electronic speckle pattern interferometry (ESPI). The correlation between the bonded area and the resonant frequency is discussed based on finite element analysis. The results indicate the possibility for in-situ evaluation of the ultrasonic bonding strength. [ABSTRACT FROM AUTHOR]

Photoacoustic flowmetry (PAF) based on time-domain cross correlation of photoacoustic signals is a promising technique for deep tissue measurement of blood flow velocity. Signal processing has previously been developed for single element transducers. Here, the processing methods for acoustic resolution PAF using a clinical ultrasound transducer array are developed and validated using a 64-element transducer array with a -6 dB detection band of 11 to 17 MHz. Measurements were performed on a flow phantom consisting of a tube (580 µm inner diameter) perfused with human blood flowing at physiological speeds ranging from 3 to 25 mm/s. The processing pipeline comprised: image reconstruction, filtering, displacement detection, and masking. High-pass filtering and background subtraction were found to be key preprocessing steps to enable accurate flow velocity estimates, which were calculated using a cross-correlation based method. In addition, the regions of interest in the calculated velocity maps were defined using a masking approach based on the amplitude of the cross-correlation functions. These developments enabled blood flow measurements using a transducer array, bringing PAF one step closer to clinical applicability. [ABSTRACT FROM AUTHOR]

We describe here an optical device, based on time-delays, for solving the set splitting problem which is well-known NP-complete problem. The device has a graph-like structure and the light is traversing it from a start node to a destination node. All possible (potential) paths in the graph are generated and at the destination we will check which one satisfies completely the problem's constrains. [ABSTRACT FROM AUTHOR]

Smog chamber experiments were conducted to study the changes of the physical properties and chemical composition of biomass burning particles as they evolve in the atmosphere. A Soot Particle Aerosol Mass Spectrometer (SP-AMS) and a Single Particle Soot Photometer (SP2) were used for the chemical characterization of the particles. An Aethalometer and a green and a blue photoacoustic extinctiometer (PAX) were used for the study of the aerosol optical properties. As smoke aged, exposed to UV light, ozone or OH radicals, organic material condensed on the preexisting particles. This coating led to an increase of the absorption of the black carbon-containing particles by as much as a factor of two. The absorption enhancement of biomass burning particles due to their coating with aromatic secondary organic aerosol (SOA) was also studied. The resulting absorption enhancement was determined mainly by the changes in the SOA mass concentration and not the changes of its oxygen to carbon ratio. The measured absorption enhancements were consistent with the predictions of Mie theory assuming core-shell morphology for the aged particles. [ABSTRACT FROM AUTHOR]

Optoacoustic imaging (OAI) is an emerging biomedical technique that allows visualization of in-depth tissues by using ultrasonic signals generated by short laser pulses. In this work, the authors combine the optical power of several pulsed high-power diode lasers (HPDLs) at 870 nm and 905 nm to a 7-to-1 675-µm fiber bundle to generate optoacoustic (OA) signals from different mixtures of two gold nanorods solutions with absorbance peak at ~ 860 nm and ~ 900 nm, respectively. The pulses produced to generate OA signals are alternated between the two wavelengths by a microcontroller circuit with fast switching (0.5ms). From the amplitude of the OA signals, the concentrations of the nanoparticles solutions are easily estimated with high accuracy using a fluence model. The results achieved with the proposed system show very good agreement between the concentrations of gold nanorods estimated from measurements and the expected values. [ABSTRACT FROM AUTHOR]

Organometallic carbonyl clusters (OMCC) of group VIII elements are water soluble, bio-compatible and stable high-contrast photoacoustic agents for live cell imaging. But, they have limited application due to weak absorption within 700–1000 nm wavelength which is known as the biological window of absorption. In this article, we report that hexa-nuclear iron (Fe 6 ) carbonyl cluster derivatized with sodium thio-propanoate has very good absorption within 700–1600 nm wave length. This modeled compound is water soluble and bio-compatible. The bio-compatibility of this compound is tested through cytotoxicity, Log P and metabolic probability at CYP450-2D6 enzyme. [ABSTRACT FROM AUTHOR]

Many applications of thin films necessitate detailed information about their thicknesses and sound velocities. Here, we study SiO2/LiNbO3 layer systems by picosecond photoacoustic metrology and measure the sound velocities of the respective layers and the film thickness of SiO2, which pose crucial information for the fabrication of surface-acoustic-wave filters for communication technology. Additionally, we utilize the birefringence and the accompanying change in the detection sensitivity of coherent acoustic phonons in the LiNbO3 layer to infer information about the LiNbO3 orientation and the layer interface. [ABSTRACT FROM AUTHOR]

We investigate the feasibility of photoacoustic (PA) imaging to quantify the concentration of surfacelocalized nanoparticles, using tissue-mimicking phantoms and imaging with a commercial PA instrument at 815 nm and a linear-array transducer at a center frequency of 40 MHz. The nanoparticles were J-aggregating porphysomes (JNP) comprising self-assembling, all-organic porphyrin-lipid micelles with a molar absorption coefficient of 8.7 × 108 cm-1 M-1 at this wavelength. The PA signal intensity versus JNP areal concentration followed a sigmoidal curve with a reproducible linear range of ∼17 fmol/mm2 to 11 pmol/mm2, i.e., ∼3 orders of magnitude with ±34% error. For physiologically-relevant conditions (i.e., optical scattering-dominated tissues: transport albedo >0.8) and JNP concentrations above ∼330 fmol/mm2, the PA signal depends only on the nanoparticle concentration. Otherwise, independent measurement of the optical absorption and scattering properties of the underlying tissue is required for accurate quantification. The implications for surface PA imaging, such as in the use of targeted nanoparticles applied topically to tissue as in endoscopic diagnosis, are considered. [ABSTRACT FROM AUTHOR]

Genetically encoded contrast in photoacoustic imaging (PAI) is complementary to the intrinsic contrast provided by endogenous absorbing chromophores such as hemoglobin. The use of reporter genes expressing absorbing proteins opens the possibility of visualizing dynamic cellular and molecular processes. This is an enticing prospect but brings with it challenges and limitations associated with generating and detecting different types of reporters. The purpose of this review is to compare existing PAI reporters and signal detection strategies, thereby offering a practical guide, particularly for the nonbiologist, to choosing the most appropriate reporter for maximum sensitivity in the biological and technological system of interest. [ABSTRACT FROM AUTHOR]

The acoustic properties of the photoacoustic Helmholtz cell can be improved by conical modification of the duct ends. The cone profile of the duct ends was studied, and according to the previous work, not all modifications of the parameters provide an increase of the Q-factor of the resonator. The aim of this work is to investigate the influence of the conical modification of the duct using a step-approximated model. [ABSTRACT FROM AUTHOR]

In optoacoustic (photoacoustic) systems, different echo signal intensities such as amplitudes, center frequencies, and bandwidths need to be compensated by utilizing variable gain or time-gain compensation amplifiers. However, such electronic components can increase system complexities and signal noise levels. In this paper, we introduce a double-Gauss lens to generate a large field of view with uniform light intensity due to the low chromatic aberrations of the lens, thus obtaining uniform echo signal intensities across the field of view of the optoacoustic system. In order to validate the uniformity of the echo signal intensities in the system, an in-house transducer was placed at various positions above a tissue sample and echo signals were measured and compared with each other. The custom designed double-Gauss lens demonstrated negligible light intensity variation (±1.5%) across the illumination field of view (~2 cm diameter). When the transducer was used to measure echo signal from an eye of a bigeye tuna within a range of ±1 cm, the peak-to-peak amplitude, center frequency, and their −6 dB bandwidth variations were less than 2 mV, 1 MHz, and 6%, respectively. The custom designed double-Gauss lens can provide uniform light beam across a wide area while generating insignificant echo signal variations, and thus can lower the burden of the receiving electronics or signal processing in the optoacoustic system. [ABSTRACT FROM AUTHOR]

Inspired by the recent advances on minimizing nonsmooth or bound-constrained convex functions on models using varying degrees of fidelity, we propose a line search multi-grid (MG) method for full-wave iterative image reconstruction in photoacoustic tomography (PAT) in heterogeneous media. To compute the search direction at each iteration, we decide between the gradient at the target level, or alternatively an approximate error correction at a coarser level, relying on some predefined criteria. To incorporate absorption and dispersion, we derive the analytical adjoint directly from the first-order acoustic wave system. The effectiveness of the proposed method is tested on a total-variation penalized Iterative Shrinkage Thresholding algorithm (ISTA) and its accelerated variant (FISTA), which have been used in many studies of image reconstruction in PAT. The results show the great potential of the proposed method in improving speed of iterative image reconstruction. [ABSTRACT FROM AUTHOR]

Photoacoustic microscopy (PAM) is a scalable bioimaging modality; one can choose low acoustic resolution with deep penetration depth or high optical resolution with shallow imaging depth. High spatial resolution and deep penetration depth is rather difficult to achieve using a single system. Here we report a switchable acoustic resolution and optical resolution photoacoustic microscopy (AR-OR-PAM) system in a single imaging system capable of both high resolution and low resolution on the same sample. Lateral resolution of 4.2 μm (with ~1.4 mm imaging depth) and lateral resolution of 45 μm (with ~7.6 mm imaging depth) was successfully demonstrated using a switchable system. In vivo blood vasculature imaging was also performed for its biological application. [ABSTRACT FROM AUTHOR]

We introduce a finite-difference frequency-domain algorithm for coupled acousto-optic simulations. First-principles acousto-optic simulation in time domain has been challenging due to the fact that the acoustic and optical frequencies differ by many orders of magnitude. We bypass this difficulty by formulating the interactions between the optical and acoustic waves rigorously as a system of coupled nonlinear equations in frequency domain. This approach is particularly suited for on-chip devices that are based on a variety of acousto-optic interactions such as the stimulated Brillouin scattering. We validate our algorithm by simulating a stimulated Brillouin scattering process in a suspended waveguide structure and find excellent agreement with coupled-mode theory. We further provide an example of a simulation for a compact on-chip resonator device that greatly enhances the effect of stimulated Brillouin scattering. Our algorithm should facilitate the design of nanophotonic on-chip devices for the harnessing of photon-phonon interactions. [ABSTRACT FROM AUTHOR]

A novel numerical study based on the finite element method is developed to demonstrate the beatlengths induced by high frequency acoustic modes inside an optical fiber for the first time. A practical methodology to model, compute and analyze the multimode interaction in the fiber is exemplified with a detailed numerical experiment. The frequency response of 1 mm long standard fiber is evaluated from 30 to 60 MHz, corresponding to the highest attenuation band of experimental fiber optoacoustic devices. The 3D simulated complex ultrasonic fields are decomposed and characterized with the averaged peak-to-peak method and 2D Fourier transform. The resulting dispersion spectra are compared and theoretically validated by the recognized Pochhammer-Chree solutions. The acoustic parameters required to modulate optical fibers are derived from the simulations and discussed. A route to overcome the frequency-induced limitations of the current devices is provided, pointing out new research possibilities for the development of highly efficient and compact all-fiber acousto-optic modulators and fiber-optic ultrasonic sensors. • First study of beatlengths induced by acoustic modes interacting in an optical fiber. • 3D design, modeling, and analysis of high frequency ultrasound with finite elements. • 2D spectral analysis of complex modal interference and dispersion inside the fiber. • Simulated beatlength-tunable acoustic gratings strengthen in-core interaction. • High efficiency for all-fiber acousto-optic modulators and optoacoustic sensors. [ABSTRACT FROM AUTHOR]

We have constructed a prototype photoacoustic mammography system (PAM-02) capable of simultaneously acquiring photoacoustic (PA) and ultrasound (US) images. Each PA, US, and fused PA/US image can be acquired over a wide area of the breast using the scanning module of a US transducer, a PA detector, and optical prisms. The resolution of the PA images exhibits improvement from 2 to 1 mm compared to images acquired using our previous prototype. The maximum scan area of PAM-02 is 90 mm along the horizontal axis and 150 mm along the vertical axis. In a phantom experiment, the available depth was at least 45 mm. A representative example of the application of the PAM-02 prototype in clinical research at Kyoto University is presented and shows S-factor images, which are considered an approximation parameter related to hemoglobin saturation of tumor-related blood vessels. We confirmed the applicability of the system for anatomical and biological research. [ABSTRACT FROM AUTHOR]

Noninvasive real-time temperature imaging during thermal therapies is able to significantly improve clinical outcomes. An optoacoustic (OA) temperature monitoring method is proposed for noninvasive real-time thermometry of vascularized tissue during cryotherapy. The universal temperature-dependent optoacoustic response (ThOR) of red blood cells (RBCs) is employed to convert reconstructed OA images to temperature maps. To obtain the temperature calibration curve for intensity-normalized OA images, we measured ThOR of 10 porcine blood samples in the range of temperatures from 40°C to -16°C and analyzed the data for single measurement variations. The nonlinearity (ΔTmax) and the temperature of zero OA response (T0) of the calibration curve were found equal to 11.4 ± 0.1°C and -13.8 ± 0.1°C, respectively. The morphology of RBCs was examined before and after the data collection confirming cellular integrity and intracellular compartmentalization of hemoglobin. For temperatures below 0°C, which are of particular interest for cryotherapy, the accuracy of a single temperature measurement was ±1°C, which is consistent with the clinical requirements. Validation of the proposed OA temperature imaging technique was performed for slow and fast cooling of blood samples embedded in tissue-mimicking phantoms. [ABSTRACT FROM AUTHOR]

Laser photocoagulation is an established treatment for a variety of retinal diseases. However, when using the same irradiation parameter, the size and strength of the lesions are unpredictable due to unknown inter- and intraindividual optical properties of the fundus layers. The aim of this work is to investigate a feedback system to generate desired lesions of preselectable strengths by automatically controlling the irradiation time. Optoacoustics were used for retinal temperature monitoring. A 532-nm continuous wave Nd:YAG laser was used for photocoagulation. A 75-ns∕523-nm Q-switched Nd:YLF laser simultaneously excited temperature-dependent pressure transients, which were detected at the cornea by an ultrasonic transducer embedded in a contact lens. The temperature data were analyzed during the irradiation by a LabVIEW routine. The treatment laser was switched off automatically when the required lesion strength was achieved. Five different feedback control algorithms for different lesion sizes were developed and tested on rabbits in vivo. With a laser spot diameter of 133 μm, five different lesion types with ophthalmoscopically visible diameters ranging mostly between 100 and 200 μm, and different appearances were achieved by automatic exposure time control. The automatically controlled lesions were widely independent of the treatment laser power and the retinal pigmentation. [ABSTRACT FROM AUTHOR]

The elastic property of the film-substrate interface of thin-film systems is characterized with an opto-acoustic method. The thin-film specimens are oscillated with an acoustic transducer at audible frequencies, and the resultant harmonic response of the film surface is analyzed with optical interferometry. Polystyrene, Ti, Ti-Au and Ti-Pt films coated on the same silicon substrate are tested. For each film material, a pair of specimens is prepared; one is coated on a silicon substrate after the surface is treated with plasma bombardment, and the other is coated on an identical silicon substrate without a treatment. Experiments indicate that both the surface-treated and untreated specimens of all film materials have resonance in the audible frequency range tested. The elastic constant of the interface corresponding to the observed resonance is found to be orders of magnitude lower than that of the film or substrate material. Observations of these resonance-like behaviors and the associated stiffness of the interface are discussed. [ABSTRACT FROM AUTHOR]

The collinear acousto-optical transformation of Bessel light beams in biaxial gyrotropic crystals into two annular, internal conical refraction beams with orthogonal elliptical polarization is studied. It is found that the diffraction efficiency is maximal (~50-60%) for low ultrasound intensities and varies slightly with further increases in acoustic power. At high ultrasound intensities, the intensities of the transmitted and diffracted annular beams differ insignificantly. The possible use of this acousto-optical interaction for creating collinear tuneable narrow-band acousto-optical filters at low ultrasonic frequencies is demonstrated. [ABSTRACT FROM AUTHOR]

We have measured local elastic moduli of particle-filled B83 babbitt-matrix composite materials produced by powder metallurgy techniques and containing silicon carbide (SiC) ceramic and modified shungite rock particles as fillers. The measurements were made by an optoacoustic laser method, whose basic principle is to determine the phase velocities of thermo-optically excited longitudinal and shear ultrasonic waves. The addition of 3 wt % of high-modulus SiC particles tends to increase the Young's and shear moduli (by 10-12%) and decrease Poisson's ratio (by 5%) relative to a hot-pressed B83 babbitt sample without fillers. [ABSTRACT FROM AUTHOR]

High fidelity optoacoustic (photoacoustic) tomography requires dense spatial sampling of optoacoustic signals using point acoustic detectors. However, in practice, spatial resolution of the images is often limited by limited sampling either due to coarse multi-element arrays or time in raster scan measurements. Herein, we investigate a method that integrates information from multiple optoacoustic images acquired at sub-diffraction steps into one high resolution image by means of an iterative registration algorithm. Experimental validations performed in target phantoms and ex vivo tissue samples confirm that the suggested approach renders significant improvements in terms of optoacoustic image resolution and quality without introducing significant alterations into the signal acquisition hardware or inversion algorithms. [ABSTRACT FROM PUBLISHER]

A miniaturized photoacoustic spectroscopic gas sensor for room climate monitoring is presented with the measurement range of 0 –5000 ppm. The sensor consists of an innovative photoacoustic detection unit with an integrated mobile phone microphone as pressure sensor. As IR-source a broadband thermal emitter is used. The emitter is modulated with 13 Hz at a maximum temperature of about 750 °C. An electronic unit with a microcontroller on a 3D-PCB design has been developed. The sensor reaches a resolution better than 50 ppm CO 2 . A detailed characterization of the setup has been carried out. An integrated temperature compensation is realized to improve the sensor performance under varying environmental conditions. The potential for further miniaturization and the realization as a low-cost mass market sensor is shown. [ABSTRACT FROM AUTHOR]

Optical-resolution photoacoustic microscopy (ORPAM) in theory provides lateral resolution equivalent to the optical diffraction limit. Scattering media, such as biological turbid media, attenuates the optical signal and also alters the diffraction-limited spot size of the focused beam. The ORPAM signal is generated only from a small voxel in scattering media with dimensions equivalent to the laser spot size after passing through scattering layers and is detected by an acoustic transducer, which is not affected by optical scattering. Thus, both ORPAM and confocal laser scanning microscopy (CLSM) reject scattered light. A multimodal optical microscopy platform that includes ORPAM and CLSM was constructed, and the lateral resolution of both modes was measured using patterned thin metal film with and without a scattering barrier. The effect of scattering media on the lateral resolution was studied using different scattering coefficients and was compared to computational results based on Monte Carlo simulations. It was found that degradation of lateral resolution due to optical scattering was not significant for either ORPAM or CLSM. The depth discrimination capability of ORPAM and CLSM was measured using microfiber embedded in a light scattering phantom material. ORPAM images demonstrated higher contrast compared to CLSM images partly due to reduced acoustic signal scattering. [ABSTRACT FROM AUTHOR]

Photoacoustic cavitation (PAC) is the formation of bubbles in liquids using a focused laser and a pre-established ultrasound synchronously. The decreased threshold of each modality and the precise location of cavitation determined by the focused laser are both significant in the targeted theranostics. In this study, PAC nucleation was described using the modified classical nucleation theory by Kashchiev's scaling function. A two-stage model of the PAC bubble dynamics was presented based on the two different bubble behaviors. It was clarified that both negative acoustic pressure and laser-induced temperature rise, resulting in the decrease in critical radius and the increase in nucleation rate, and thereby contribute to the increase in nucleation probability in the confocal region. Ultrasound determined the whole PAC bubble dynamics with temperature-dependent parameters, while the laser mainly contributed to its initial conditions. Moreover, the effects of certain parameters on PAC were further discussed, including the relative acoustic phase when a laser is introduced (φ), laser pulse duration (τL), laser focus radius (Rf), and ultrasound amplitude (PA). The model would be helpful in understanding the PAC process and further in introducing PAC to potential targeted theranostics. [ABSTRACT FROM AUTHOR]

Photoacoustic tomography (PAT) is an effective optical biomedical imaging method characterized with non-ionizing and noninvasive, presenting good soft tissue contrast and excellent spatial resolution. To build a full-view photoacoustic (PA) image, numbers of ultrasound sensors are needed to assure the image quality, which will bring difficulties to data acquisition and real-time image display. Compressed sensing (CS) theory breaks the restriction of Nyquist sampling theorem and is capable to rebuild signals with less measurements. In this contribution, we proposed an optimization method to increase image quality of full-view PAT with less ultrasound sensors, which combines the theory of CS and a circularly distributing asymmetric data acquisition frame. The hardware cost can be saved and time efficiency of PAT can be raised without sacrificing the image quality. The feasibility of our proposed method is verified in simulation experiments which yield expected results. Our study might be helpful for clinical medical imaging such as early stage breast cancer detection, endoscopic imaging and in vivo monitoring. [ABSTRACT FROM AUTHOR]

Electrostatically actuated microelectromechanical system (MEMS) oscillators are limited to few megahertz–gigahertz range on account of transduction inefficiency at higher frequencies. Piezoelectric transduction affords lower motional impedances at high frequencies, however mass-loading on account of metal electrodes imposes practical limits on the mechanical quality factor of piezoelectric resonators in the gigahertz frequency regime. In this paper, we present a silicon optoacoustic oscillator operating at 2.05 GHz with signal power 18 dBm and phase noise −80 dBc/Hz at 10-kHz offset from carrier. We employ displacement amplification and partial air gap capacitive transduction to enhance the transduction efficiency. An unconventional photolithography step is performed on a released MEMS structure, which greatly simplifies the fabrication process and allows electrical contact with the electrodes. Built-in nonlinear optomechanical modulation provides noiseless up-conversion of the oscillation signal all the way up to 16.4 GHz with −45-dBm signal power. We develop a phase noise model for the oscillator and identify the photodetector shot noise to be the dominant noise source. Using a high gain and low noise avalanche photodetector enables reduction of the far-from-carrier phase noise floor by 15dB. The phase noise model provides insights into understanding the influence of laser detuning on the oscillator noise performance, which has not been studied to date. [2013-0291] [ABSTRACT FROM AUTHOR]

Basing on the comprehensive studies of acoustic properties for NaBi(MoO4)2 crystals, we have determined the full matrices of elastic stiffness and compliance coefficients and constructed cross sections of acoustic-wave velocity surfaces by the principal crystallographic planes. We have shown that the slowest acoustic wave propagates in the ab plane at the angle 61.9 deg with respect to the a axis and has the velocity ~ 1948 m/s. The interaction with that wave is expected to provide the highest acoustooptic figure of merit. Deviations of polarization states of the acoustic waves from the purely longitudinal and transverse types and deviations of the acoustic energy flux from the wave vector direction are analyzed for the NaBi(MoO4)2 crystals. [ABSTRACT FROM AUTHOR]

A high-precision laser range finder based on highly stable synchronous measuring wavelengths with a large range is proposed in this paper. In this method, the coarse and fine measuring wavelengths are generated by the beat signals of lasers in different frequencies. The lasers are produced by frequency shifting one laser mode with three acousto-optic modulators working at different frequencies. To realize an appropriate coarse and fine measuring wavelengths for the required measurement range and resolution, the driving frequencies of the acousto-optic modulators are controlled by direct digital synthesizer (DDS) in high precision. At the same time, the frequency drift of the laser source and other common errors are reduced by applying the optical heterodyne effect. Consequently, the stability of measuring wavelengths is significantly improved. Furthermore, an improved digital method of phase measurement with same basic clock DDS is proposed to achieve synchronous phase measurement with a little error. Results from the experiments show that the measuring frequency stability is better than 1.75 \times 10^-9 ( $\tau =100$ s), and a measurement with relative uncertainty of 0.63\times 10^{-6} at a distance of 100 m is achieved under laboratory conditions. [ABSTRACT FROM PUBLISHER]

For CaWO calcium-tungstate crystals based of piezooptic π and elastic C coefficients, we fill the matrix of elastooptic constants p and compute the errors of their determination. We reveal the following empirical regularity: the signs of piezo- and elastooptic coefficients with identical subscripts coincide. It is shown that this law remains true for some other low-symmetry crystals that belong to different symmetry classes. Calcium tungstate dominates over some known acoustooptic materials by the higher values of elastooptic coefficients and, hence, is a promising material for applications in acoustooptic devices. [ABSTRACT FROM AUTHOR]

Detection of orthotopic xenograft tumors is difficult due to poor spatial resolution and reduced image fidelity with traditional optical imaging modalities. In particular, light scattering and attenuation in tissue at depths beyond subcutaneous implantation hinder adequate visualization. We evaluate the use of multispectral optoacoustic tomography (MSOT) to detect upregulated epidermal growth factor (EGF) receptor in orthotopic pancreatic xenografts using a near-infrared EGF-conjugated CF-750 fluorescent probe. MSOT is based on the photoacoustic effect and thus not limited by photon scattering, resulting in high-resolution tomographic images. Pancreatic tumor-bearing mice with luciferase-transduced S2VP10L tumors were intravenously injected with EGF-750 probe before MSOT imaging. We characterized probe specificity and bioactivity via immunoblotting, immunocytochemistry, and flow cytometric analysis. In vitro data along with optical bioluminescence/fluorescence imaging were used to validate acquired MSOT in vivo images of probe biodistribution. Indocyanine green dye was used as a nonspecific control to define specificity of EGF-probe accumulation. Maximum accumulation occurred at 6 hours postinjection, demonstrating specific intratumoral probe uptake and minimal liver and kidney off-target accumulation. Optical bioluminescence and fluorescence imaging confirmed tumor-specific probe accumulation consistent with MSOT images. These studies demonstrate the utility of MSOT to obtain volumetric images of ligand probe biodistribution in vivo to detect orthotopic pancreatic tumor lesions through active targeting of the EGF receptor. [ABSTRACT FROM AUTHOR]