This PDF file contains the front matter associated with SPIE Proceedings Volume 11210, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

On September 28, 2019, the acousto-optics community was deeply saddened with the passing of Vitaly Borisovich Voloshinov, Professor of the Lomonosov Moscow State University, who significantly contributed to many Schools on Acousto-Optics and Applications. In this article, we would like to pay tribute to the memory of Prof. Voloshinov by presenting his remarkable contribution in research, teaching, engineering and organization.

Some personal recollections on the acousto-optics as an interesting field of physics and its applications will be shared with the participants in a short welcome address. The consecutive number of the present Spring School on AO and A, 14-th, indicates a long history of events (39 years) initiated in 1980 by the University of Gdańsk as the triennial international meeting of specialists of science and technology over the world, being continued till now.The fundamentals of the acousto-optics domain covering light (fotons) and ultrasonics (fonons) interactions originally come from works of L. N. Brillouin whose anniversaries the 130 years of his birthday and the 50 years of his death are being celebrated during the current year. The next principles were widely developed by many others in 1930’s after essential two independent papers by P. Debye and F. W. Sears (USA) and R. Lucas and P. Biquard (France), then fundamentals by C.V. Raman and N. S. Nagendra Nath, followed by many papers and applications after the II World War. The wide and rich literature of the subject of the last 100 years built up a branch of knowledge to which a piece of contribution of the AO and A Schools has its own place. The further development of the branch is prospective, too. Recently, such problems as very short time (pico- and femtoseconds) acousto-optic interactions, nonlinear processes in bio- and nano-structures and their applications in acousto-optic and optoelectronic instrumentation as well as many others are subjects of the current interest and promising topics for the future.

Laser ultrasonic tomography uses pulsed laser light for photoacoustic excitation of short probe ultrasonic pulses in a special light-absorbing plate. These pulses propagate through the immersion liquid, then they are reflected from the surface of the object and scattered by the inhomogeneities inside the object. Scattered and reflected waves are recorded by a broadband multi-element piezoelectric array and used to reconstruct the image. The wide spectral band (0.1-15 MHz) of probe pulses is well suited to the problem of inspection of carbon-fiber-reinforced polymers (CFRPs), allowing visualization of individual carbon fiber layers and defects with high accuracy. In this paper, laser ultrasonic tomography is proposed for inspection of CFRPs. The experimental results of the inspection of a graphite-epoxy composite sample with inclusions and defects are presented.

The accurate theory describing interaction of two coherent light beams with ultrasonic wave where one of the light beam is incident at positive Bragg angle while the other at negative was developed by Leroy and Blomme in 1984 . The assumed geometry in this theory resembles an interferometer wherein ultrasonic beam plays a role of the output beam splitter of the light. The output light intensity is modulated with ultrasonic frequency as a result of interference between the light in diffraction orders in which the frequency is changed due to the Doppler effects with those diffracted with unchanged frequency. Temporal modulation of the light intensities in diffraction orders, that was foreseen by Leroy and Blomme, was confirmed experimentally and the results will be presented. In addition, the Leroy-Blomme theory has been extended to include the effect of the initial phase of the ultrasonic wave on the phase of modulation of light intensity in diffraction orders. According to the best knowledge of the author, Leroy and Blomme theory has not been verified experimentally, although many years have passed. This theory could be applied to the quantum optics phenomenon when pairs of entangled photons are incident on ultrasonic wave instead of two coherent light beams. The geometry of interaction of two coherent light beams with ultrasonic wave in Leroy-Blomme theory is the same as for Hong-Ou-Mandel interferometer wherein a beam splitter is replaced by the ultrasonic wave. Similarities and differences between Leroy-Blomme and Hong-Ou-Mandel interferometers will be presented.

We examined optic, acoustic and acousto-optic properties of materials belonging to the borate family of trigonal crystals α-BaB₂O₄ and β-BaB₂O₄. Phase velocities of acoustic waves and frequency dependences of Bragg angles were calculated in the crystals. Figure of merit magnitudes were evaluated in XZ, YZ and in a few other planes of the materials. The analysis was carried out in order to find a possibility of using the materials in acousto-optic deflectors and filters operating in the visible light and also in the ultraviolet region of spectrum.

Acousto-optical tunable filters (AOTFs) are well used for practical applications and are most often based on the classical anisotropic non-collinear configuration in tellurium dioxide crystals. Any product sheet of such a commercially available AOTF presents two main features: the tuning range and the spectral bandwidth Δλ. The spectral transmission bandwidth1 is proportional to the ratio λ² /(bW) where λ is the optical wavelength, b the dispersive constant and W the length of the transducer. The dispersive constant b is a rapidly decreasing function of the wavelength in the blue visible spectrum. As for examples: for a one octave tuning range starting from 400 nm to 800 nm, the spectral bandwidth is multiplied by ~10. For a tuning range in the infrared band 1250-2500 nm, the spectral bandwidth is multiplied by ~4. We present the design of a filter operating in the visible region from 450 nm to 650 nm. A double anisotropic interaction² is considered allowing the simultaneous diffraction of the two optical modes propagating into the crystal by a single ultrasonic wave. A multi-electrode array of three identical consecutive electrodes W_i:1-3 = 3 mm is deposited on the transducer leading to a more precise control of the spectral bandwidth. The acousto-optic device has been fabricated by the AA-Opto company. With this component the spectral bandwidth is only multiplied by ~2 on from 400 nm to 650 nm.

We analyze the relations between discrete RF signals and their spectra from the point of view of the sampling theorem and properties of discrete Fourier transform. The RF waveforms with given duration and spectral bandwidth are used for controlling acousto-optic tunable filters in programmable broadband transmission mode. It is demonstrated that the maximum second order dispersion of the AOTF is reduced by the factor of 2 compared to a linear chirped signal with the same bandwidth and duration. This analysis is important for applications in precision ultrafast laser pulse shaping and adaptive spectroscopy.

Acousto-optic (AO) modulator applying standing acoustic wave and utilized for active laser mode locking is prone to temperature fluctuations, which result in operation efficiency deviations. In this study we examine the effects of electrical matching circuit characteristics on the parameters of acoustic resonances and AO diffraction in the AO cell both theoretically and experimentally. The ways to utilize this effect for compensation of the thermal influence on AO diffraction are outlined. Our analysis allows broadening the temperature and power domains of an AO mode lockers reliable operation without adding special temperature stabilization system.

This work is devoted to generalization of experimental researches results of acousto-optic filters instrumental functions at frequency modulation of an ultrasonic wave.

This paper describes the development, manufacturing and testing of acoustooptic (AO) modulator made of bismuth sodium molybdate NaBi(MoO₄)₂ crystal. Despite the rather long interest in NaBi(MoO₄)₂ crystals as possible AO material, there is no information about their practical use in acousto-optics. The isotropic orthogonal interaction geometry was used, a longitudinal piezoplate was used as a piezoelectric transducer, the acoustic wave was directed along the crystallographic axis Z. The modulator has shown a high diffraction efficiency (up to 87%) with an RF power of 2.5 W. NaBi(MoO₄)₂ is characterized by manufacturability during crystal growing and during mechanical processing and optical homogeneity

Biofilms formed on solid biotic and abiotic substrata, deployed for a certain time period in the coastal waters of the Baltic, were studied with a photoacoustic spectroscopy (PA) technique. Since periphyton appears to be an effective indicator of water quality and stands for a photosynthetic system with a variety of pigments, the aim of the study was to determine biofilm colony photosynthetic apparatus properties (photosynthetic energy storage (ES), PA amplitude and phase spectra) which exhibited a seasonal variability. Nutrient limitation and antrophogenic eutrophication are among the most important factors determining the overall status of water bodies which can be followed by ES efficiency of biofilm cultures. ES turned out to be inversely correlated to biogenic elements concentrations (N (R=-0.76); P (R=-0.81); O (R=-0.67), and positively correlated to primary production (R=0.86) and Chl. a concentration (R= 0.82) in the Baltic (seawater parameters data available at http://satbaltyk.iopan.gda.pl). Photoacoustics can be used to estimate the concentration of photosynthetic pigments in cultures, the efficiency of ES by periphyton photosynthesis can be directly determined by photoacoustics, the effects of environmental stressors: temperature, nutrient limitation, high/dim light and pollutants on the photosynthetic capacity of biofilm colonies can be evaluated.

Endoscopic imaging systems are widely used for non-invasive diagnostics of inner tissues for biomedical applications as well as for non-destructive testing of various hard-to-reach industrial objects. Conventional white light endoscopy often does not provide contrast visualization of the inspected objects and quantitative characterization of their differences. In these cases, spectral imaging techniques may be helpful to increase the effectiveness of endoscopic inspection. Acoustooptic (AO) filtration of light is a very promising technique for implementing spectral imaging capabilities. In this paper, we discuss the peculiarities and benefits of conjugating AO tunable filters (AOTF) with rigid borescopes, flexible fiberscopes and video endoscopes. We analyze and compare imaging and spectroscopy capabilities of two alternative technical implementations: AOTF-based tunable light sources and AOTF-based add-on imaging modules. The results of this analysis are confirmed by multiple experiments.

In this paper, we present results of theoretical and experimental investigation of the crystal KRS-5. The carried out research was related to analysis of acoustic, optic and acousto-optic properties of the single crystal KRS-5 that is a solid solution of thallium halides. The material is considered as a medium for applications in infrared acousto-optic devices providing laser beam control. In our analysis, we determined acoustic properties of the material. The values of acoustic phase velocities and their polarization directions were determined for acoustic modes propagating along in the directions [100], [110] and [111]. We also determined the velocities and polarizations of the acoustic waves in the planes (001) and (1 1 0) of the material. In the basic experiment, we used the slow shear acoustic wave propagating along the direction [100] and having the phase velocity value V= 890 m/s. One of the principal goals of the research was directed to experimental confirmation of a possibility to induce birefringence in the cubic material. We managed to induce the birefringence applying an external static pressure to the crystal. Varying the pressure, we controlled the birefringence and obtained difference in magnitudes of the refraction indexes up to Δn =3.5·10^-4 . Typical regimes of anisotropic acousto-optic interaction in the birefringent medium were observed. The theoretical results were confirmed by experiments including laser probing of acoustic beams and analysis of Schaefer-Bergmann diagrams. The carried out investigation confirmed the conclusion that the single crystal KRS-5 is a promising material for the applications in the infrared acousto-optic devices.

We describe near-infrared acousto-optic (AO) spectrometer ISEM (Infrared Spectrometer for ExoMars) developed for ExoMars 2020 space mission. The instrument goal is to investigate Martian surface and in particular to study mineralogical and, probably, petrographic composition of the uppermost regolith layer of the regolith by measuring reflected solar radiation in the near infrared spectral range. The instrument covers the wavelength range from 1.15 to 3.3 μm with the spectral resolution of ~25 cm^-1 and has a circular field of view (FOW) of about 1°. The spectrometer consists of two parts: optical box and electronic box. The optical box is to be mounted on the top of the Martian rover’s mast providing better field of vision. Here we present the instrument description and optical design as well as the first results of laboratory calibrations and ground-based measurements of the Martian analogue samples.

Optical frequency combs (OFC) occupy an important place in modern optoelectronics. Plenty of OFC generation methods and practical application concepts were proposed in recent decade. Among the generation methods are several based on acousto-optic (AO) interaction application. In this paper we theoretically examine new OFC generation method based on joint use of collinear AO diffraction and frequency-shifting loop. This method gives two novel OFC generation schemes. The first one contains collinear AO cell driven by radio-frequency (RF) generator and optical loop connecting optical output and input of the AO cell. The second one includes not only the optical loop but also the optoelectronic feedback connecting the optical output of the system with the piezoelectric transducer of the AO cell. In this case the system operates above the self-excitation threshold without RF generator. Both systems were examined theoretically, it was discovered that they give the possibility to generate OFC’s in several ways. The switching between them is realized by mutual reorientation of a pair of polarizers placed before and behind the AO cell and achromatic half-wave plate included in the optical feedback loop. It is shown that the parameters OFCs obtained in the system with only optical feedback are determined by AO cell material, RF generator signal frequency and magnitude, optical loss and amplification. The system with both optic and electronic feedback gives the unique opportunity to obtain chirped OFCs.

Acousto-optical filters are devices in which light dispersion occurs through a crystalline translucent material. Particularly, light interacts with a sound-induced spatially distributed. Post-interaction, diffracted light can be analyzed for different purposes. Although acousto-optics has been studied for decades, practical devices applying its principles are relatively recent. Here, experimental and technical procedures are used to obtain the transfer function of an acousto-optical tunable filter (AOTF) based system used as a hyper-spectral photometer. The reflectance responses at given wavelengths are measured and adjusted from a commercially available color pattern set, while typically, those values are set up manually. We propose a semiautomatic strategy to calibrate as a single black box all components of the system including: the light source, the signal generator power with its frequency-amplitude deviation from the full radio frequency set point, the radio-frequency amplifier, the transmission lines, the piezoelectric impedance, and the filter's own transfer function among others. To achieve that, we explored the capability of neural networks with deep learning. The system's input is reflectance data measured with a spectrophotometer at wavelengths from 400 to 700 nm with a step of 10 nm. Then, the AOTF system was used to gather reflectance data from those color pattern tiles from 400 to 700 nm with a step of 1 nm. Both reflectance datasets were adjusted using the proposed deep learning neural network. Results show that it is possible to calibrate an AOTF system by using ceramic tile color patterns and measuring reference reflectance values with a spectrophotometer in the visible range. Furthermore, a neural network can be trained to learn the compensation values, deriving trustable spectral information with a better wavelength resolution.

In this work we present the broadband characterization of in-fiber acousto-optic interaction in fiber SM2000 (Thorlabs), with a special focus on the sensitivity of the technique as a measurement tool of the parameters of the fiber. The acoustooptic interaction technique provides good sensitivity when measuring parameters of singlemode or few-mode fibers: dispersion curves, radius, or core refractive indices (both linear and nonlinear) can be determined by means of this tool with accuracy. The basics of the technique rely on its resonant character: as a parameter of the fiber changes, the optical wavelength that fulfills the acousto-optic phase-matching condition shifts. The measurement of the acousto-optic phase matching curve provides information about the sensitivity of the technique as a function of variations of different parameters of the fiber. Such measurements can be performed in a broadband spectral range, using a single section of fiber of some tens of cm. In this paper, we report the measurement in detail of the acousto-optic dispersion curves for the couplings LP₀₁-LP_1,1-4, in the optical range 1.0-2.0 μm. From these data, we characterize the sensitivity of the technique for the measurement of the core radius, external radius and numerical aperture of the fiber, especially around the turning point of the phase-matching curve for the acousto-optic coupling.

A dual-wavelength narrowband all-fiber acousto-optic tunable bandpass filter (DNAOTBF) was proposed and fabricated via the different vector modes coupling based on the same scalar mode induced by the flexural acoustic wave in dispersion compensation fiber (DCF). In the experiment, the resonant dual-wavelength and coupling efficiency could be electrically tuned simultaneously with a range from 1526nm of 1565nm and the lowest 3-dB bandwidth was 0.92nm.

Acousto-optical devices, such as deflectors, modulators or filters, provide an effective way of light control and signal processing techniques. However, their operation range is limited to visible and near-infrared wavelengths due to quadratic law of efficiency decrease of acousto-optical interaction with the wavelength increase. Besides, high-quality acousto-optic materials such as TeO₂ are non-transparent at wavelengths larger than 5 µm, while the infrared optical materials provide significantly lower acousto-optic quality. Here we demonstrate how these limitations could be overcome by applying of specifically designed multilayered structures with electromagnetic modes strongly coupled to the incident light using Otto configuration of prism coupling. Such approach could be used for a novel acousto-optical device operating at 8-14 μm wavelengths. Acoustic wave is excited via a piezoelectric transducer in the prism provides modulation of the coupling intensity which results in up to 100% modulation of the transmitted light at the spatial scale less than the ultrasound wavelength. Therefore, it provides the possibility to achieve efficient acousto-optical modulation at frequencies over several gigahertz.

We present results of theoretical analysis of anisotropic acousto-optic interaction peculiarities in a spatially periodical acoustic field created by a phased array transducer with antiphase excitation of adjacent sections. Contrary to the homogeneous transducer, the transfer function of the acousto-optic cell with the phased array transducer contains two main maxima situated on the opposite sides in regard to the Bragg angle. The calculations have shown that the diffraction efficiency can reach 100% in spite of noticeable acousto-optic phase mismatch. A number of unusual features of light scattering in the spatially periodical acoustic field is revealed, which can be useful at the development of acousto-optic devices of a new type.

The paper considers optic, acoustic and acousto-optic properties of single crystal mercury bromide Hg₂Br₂. Phase velocities of acoustic waves and frequency dependences of Bragg angles in the tetragonal crystal were calculated in (001) , (010) and (110) planes. The analysis was carried out in order to find a possibility of using the material in acousto-optic deflectors and imaging filters operating in the middle and long infrared region of spectrum. Figure of merit of the crystal was evaluated in two different interaction geometries in the strongly birefringent crystalline material.

The efficient acousto-optic diffraction has been obtained using bulk acoustic waves radiated by an interdigital transducer deposited on the YX lithium tantalate substrate surface. For the case of anisotropic diffraction of the light, propagating in the plane containing the crystal Z-axis and the bulk acoustic wave vector, the frequency dependencies of light incidence and diffraction angles have been studied theoretically and experimentally. The diffraction efficiency attains 10 % with the 1 W electrical power oscillator, which is considerably higher than that for the light propagating in YX plane.

We present results of theoretical investigation of anisotropic close to collinear acousto-optic interaction in alpha-iodic acid crystal. A comparative analysis of the characteristics of quasi-collinear filters and filters based on close to collinear variant of interaction is carried out. The calculations have shown that filters based on close to collinear variant of interaction are almost as good as quasi-collinear filters in spectral resolution at the same interaction length. It is established that the effect of angular shift of geometry due to the dispersion of directions of biaxial crystal optical axes on the interaction characteristics, in this case, is much less distinct than for the wide-aperture filter in the region of small Bragg angles. This fact opens up possibilities of practical implementation of such devices without geometry of acoustooptic interaction correction.

This review presents a selection of advanced microscope designs employing acousto-optical deflectors (AODs). In the designs covered, AODs are used as tunable diffraction gratings to control complex illumination patterns at the Fourier plane of an objective lens. This approach allows us to generate desired illumination patterns at the focal plane of a light microscope. In simple terms, I will describe two established designs, the 3D Random-Access Multi-Photon Microscope and the Standing-Wave Super-Resolution Microscope, as well as two new schemes including the Random-Access STED Microscope and the Frequency-Encoded Multi-Beam Microscope. All instruments mentioned here were designed to overcome the throughput limitations of previously used light microscopes in experimental Neuroscience.

Acousto-Optic Modulators (AOM) have been used for a wide variety of signal processing application. Traditionally, they are built with bulk materials (e.g. crystal quartz, tellurium dioxide, and fused silica), which limit their operational frequency to below 300MHz. In addition, the absence of a CMOS foundry-compatible process has prevented the scalable integration, mass production, and design complexity achieved by integrated photonic devices. An effcient high-frequency AOM can be the building block for different applications, such as a high-speed spatial light modulator with tens of MHz bandwidth, or a viable free space optical interconnect link between processors and memory that meets the stringent energy and bandwidth constraints. We report the operation of an AOM with operation frequency between 300 MHz and 3.5 GHz realized by MEMS foundry (Piezo-MUMPS) platform. Preliminary results on the detection of weak RF signal is reported.

Laser-based systems are fundamental tools in several research and industrial fields as important as optical imaging and material processing. They grant high precision and flexibility, though, the throughput of these processes is constrained by their inherent point-scanning nature. An effective solution to this problem is beam parallelization, though, current implementations suffer from lack of flexibility, long response time or optical aberrations. In order to overcome these issues, we propose an original acousto-optofludic (AOF) device that exploits mechanical vibrations in a liquid to diffract light in a comb of multiple beams. In this work, we detail design, implementation, and optical characterization of AOF-based multi-focal laser system. In particular, we show that the main features of the acoustically generated beamlets can be tuned by properly varying frequency, amplitude, and phase of the mechanical oscillations. The application of this device to laser direct writing will enable high throughput processes of various materials in an highly tunable way.

Acousto-optical tunable filters (AOTFs) are still little known to the Earth atmosphere remote sensing community. The bulk of passive atmospheric remote sensing instruments remains divided into two families: those relying on interferometric techniques (mostly for the long-wave absorbing species), and those based on diffraction gratings (better suited for UV-VIS absorbing species). Still, AOTFs have some unique features which should deserve more attention, in particular their angular acceptance, and their polarization sensitivity. The first one because it allows to work in an imaging setup, the second because many atmospheric processes have a polarizing effect. In this paper, we will present different AOTF-based instrument concepts (or even prototypes) which take advantage of these features in order to improve the sate-of-the-art of measurement techniques in several fields of atmospheric science. We will first present the improved NO2 camera: its new capabilites, the subsystems which have been changed, and some preliminary results. Then, we will discuss two other potential applications: the study of the solar spectral irradiance variability in the UV, and the detection of auroral polarized emissions. For each concept, we will discuss the current challenges faced by the existing instruments, and analyze how the use of AOTFs could overcome them. A suggestion for the AOTF selection will be made, and the expected instrument performance will be estimated.