Acousto-optic Diffraction Research Articles

Temperature impact on acoustic wave reflection in quasi-collinear acousto-optic devices.

Quasi-collinear geometry is a special configuration of acousto-optic (AO) diffraction that applies the acoustic wave reflection from the AO cell input optical face and provides an extremely large interaction length for achieving abnormally high spectral resolution of AO tunable filters. As a result, it becomes possible to implement the multifrequency diffraction which has found important applications for laser pulse shaping. The operation of quasi-collinear AO devices in the multifrequency diffraction regimen is accompanied by the appearance of the longitudinal and transverse temperature gradients in the crystal, mainly due to the acoustic power absorption. Temperature changes the AO cell material stiffness moduli, affecting the characteristics of the incident and reflected acoustic waves (propagation velocities and walk-off angles), and the reflection condition in general. On the example of paratellurite crystal is shown that the AO cell heating near the reflecting facet leads to a deviation of the reflected acoustic beam propagation direction from that specified during the AO cell manufacturing. The deviation magnitude depends on the reflection geometry choice and, in the paratellurite, may exceed several degrees, which adversely affects the AO diffraction characteristics, reducing the AO interaction efficiency and distorting the transmission function shape. The reflected beam deviation may be compensated by means of choosing the angle between the AO cell reflecting face and the piezoelectric transducer face, taking into account the operating AO device thermal regimen.

Quality assessment of stereoscopic images under acousto-optic diffraction in paratellurite crystal

Quality assessment of stereoscopic images under acousto-optic diffraction in paratellurite crystal

Design of a broadband acousto-optic filter using bulk acoustic wave beam steering with an interdigital transducer

Acousto-optic tunable filters are photonics devices whose operation is fundamentally based on crystal acoustics. One of the phenomena used to improve performances of bulk acousto-optic devices is acoustic beam steering. Here we present a complete analytical model, which covers bulk acoustic wave beam steering in crystals with phased-array excitation and Bragg phase matching of anisotropic acousto-optic diffraction. An interdigital phased-array transducer is proposed for laterally excited bulk acoustic wave generation enabling the effect of beam steering. The design of a paratellurite-based acousto-optic filter with extended transmitted optical wavelength range from 0.4 to 1.1μm is discussed and supported by numerical simulations.

Investigation of acousto-optic interaction with momentum mismatching considering acoustic anisotropy in birefringent crystal.

In this work, the momentum mismatching based on which the acousto-optic (AO) transfer function and diffraction efficiency was acquired, was calculated considering the properties of AO crystals in AO interactions in acousto-optic tunable filter (AOTF). Transfer functions were obtained using a 4f optical system combined with AOTF and compared with theoretical calculations. It demonstrated the influence of acoustic energy shift on the AO interaction which should be considered in the design of AOTF.

Enhancement of the Efficiency of Acousto-Optic Diffraction Due to the Ellipticity of Eigen Optical Waves, Caused by the Electro-Gyration Effect in Lead Germanate Crystals

Enhancement of the Efficiency of Acousto-Optic Diffraction Due to the Ellipticity of Eigen Optical Waves, Caused by the Electro-Gyration Effect in Lead Germanate Crystals

Collinear acousto-optic filtering of divergent optical beams in the presence of optoelectronic feedback

The divergence of a diffracting light beam affects the characteristics of acousto-optic (AO) interaction. This is due to the side components of the optical beam spatial spectrum propagating in the crystal along the directions different from the beam axis. The divergence causes the AO diffraction efficiency decrease and the distortion of the AO device transmission function — its bandwidth increases and the side lobes are smoothed. We suggest the method to compensate the optical beam effect on the collinear AO diffraction transmission functions shape based on optoelectronic feedback circuit application connecting the AO cell optical output and its piezoelectric transducer. It is shown that such method makes it possible to narrow the transmission function passband and increase the spectral contrast of the system. It is found out that feedback does not affect the AO diffraction transfer functions. Thus, the introduction of feedback makes it possible to increase the spectral resolution of AO devices without compromising the AO device angular aperture.

Generation of acoustic vortices and acousto-optic interactions with acoustic vortex beams.

We demonstrate the generation of acoustic vortex beams with the aid of an acoustic spiral phase plate and an acoustic grating having a fork-like bifurcation of its slits. The acoustic vortex beam generated in this manner influences the particles floating on a water surface and rotates them. Our experiments show that the intensity of the acoustic vortex beam increases from zero in its center to a certain maximal value near the shell of the beam. The phase of the beam changes by the angle 2π whenever the azimuthal angle is changed by the same value. We also study acousto-optic diffraction of the optical beam by the acoustic beam bearing a vortex and demonstrate that each of the appropriate diffraction maxima are split into two maxima. The latter correspond to diffraction by the elementary acoustic rays which are close to the opposite edges of the acoustic vortex beam. A dark region between the maxima appears due to destructive interference of the elementary optical rays originated from the diffraction by the opposite sides of the acoustic vortex beam, which are phase-shifted by π.

Simulation of an acousto-optic deflector of terahertz radiation based on a sectioned ultrasound transducer

Subject of study. The acousto-optic diffraction features of terahertz radiation by an ultrasonic field with periodic inhomogeneity are theoretically evaluated in this study. Aim of study. This study aims to identify the optimal parameters for implementing an effective terahertz radiation deflector. Method. Liquefied sulfur hexafluoride gas is selected as the interaction medium to enhance the energy efficiency of the deflector. Additionally, the application of a sectioned phased ultrasound transducer is proposed to increase the number of resolvable light spots. Main results. The features of the acoustic field generated by the transducer are demonstrated. Analytical relations are derived for the main parameters of the acousto-optic deflector. Practical significance. A possible fivefold increase in the number of resolvable spots compared with an acousto-optic deflector based on a single-section transducer of the same length is demonstrated.

Photon–phonon entanglement in the acousto-optic interaction of vector beams

We demonstrate that acousto-optic diffraction under certain conditions can be accompanied by inter-system photon–phonon entanglement. A photon diffracted during Stokes acousto-optic interaction of acoustic and optical vector beams represents a vector beam that manifests the intra-system entanglement between its states characterized by the different signs of circular polarization and orbital angular momentum. At the same time, a diffracted photon and an acoustic phonon emitted in the process of acousto-optic interaction demonstrate the inter-system entanglement between their circularly polarized vortex states.

Influence of Faraday elliptical birefringence on the acousto-optic diffraction efficiency: a case of isotropic interaction with quasi-longitudinal acoustic waves in KH2PO4 crystals. Errata

Influence of Faraday elliptical birefringence on the acousto-optic diffraction efficiency: a case of isotropic interaction with quasi-longitudinal acoustic waves in KH2PO4 crystals. Errata

Influence of Faraday elliptical birefringence on the acousto-optic diffraction efficiency: a case of isotropic interaction with quasi-longitudinal acoustic waves in KH2PO4 crystals

Influence of Faraday elliptical birefringence on the acousto-optic diffraction efficiency: a case of isotropic interaction with quasi-longitudinal acoustic waves in KH2PO4 crystals

Enhancement of acousto-optic diffraction efficiency in SiO2 crystals due to ellipticity of optical eigenwaves: isotropic acousto-optic interaction

Enhancement of acousto-optic diffraction efficiency in SiO2 crystals due to ellipticity of optical eigenwaves: isotropic acousto-optic interaction

Quasi-Collinear AOTF Spectral Transmission Under Temperature Gradients Aroused by Ultrasound Power Absotption.

Quasi-collinear geometry is a special configuration of acousto-optic (AO) diffraction that provides an extremely large AO interaction length for achieving extremely high spectral resolution of AO tunable filters (AOTFs). Large AO interaction length also makes it possible to implement multifrequency diffraction in quasi-collinear AOTFs, which has found multiple applications in modern optoelectronics. The most widespread of them being ultrashort laser pulse shaping when the pulse shape and spectral composition is controlled by the spectral composition of the ultrasound pulse aroused in the AO crystal. The operation of quasi-collinear AOTFs is accompanied by the appearance of the temperature gradients in the AO device mainly due to the acoustic power absorption by the material. We experimentally assessed the influence of these gradients on the AOTF spectral characteristics. A theoretical model based on the Raman-Nath equations was proposed, which allows to consider the influence of ultrasound attenuation and temperature gradients on the AOTF transmission. This model is valid for transmission simulations both in single- and modulated-frequency AOTF operation modes. The study includes the effects of acoustic wave attenuation and AO phase matching shift caused by inhomogeneous crystal temperature along the optical beam path. The compensation strategy based on ultrasound frequency and magnitude adjustment is proposed for minimizing the effect of temperature gradients and acoustic field attenuation on AOTF spectral transmission for broadband operation in ultrashort laser pulse shaping.

Acousto-optical modulation of airy light beams in crystals

The non-collinear diffraction of Airy light beams on ultrasound in the regime of weak and strong acousto-optical (AO) interaction is investigated. Expressions are obtained for the complex amplitudes of diffracted waves in the general case of an anisotropic medium. It is shown that with an increase in the dimensionless parameter of the Airy beam, the efficiency of Bragg diffraction decreases. At the same time, however, the shape of the modulation curve remains unchanged. It is established that the greatest efficiency of anisotropic Bragg diffraction is achieved for a case when the diffracted Airy beam propagates along the front of the ultrasonic wave. It is shown that the efficiency of AO diffraction of Airy beam on an amplitude-modulated wave is determined by the diffraction efficiencies of constant components in a diffracted beam.

Examination of an acoustic field longitudinal power distribution in quasicollinear acousto-optic cells

The quasicollinear geometry of acousto-optic (AO) diffraction is notable as makes it possible to achieve an extremely high AO interaction length and, consequently, an anomalously high spectral resolution for AO devices. This geometry is especially convenient for the implementation of multifrequency AO diffraction, which has found wide application for solving the problems related to the laser pulse shaping. Since acoustic beams propagate over long distances in quasicollinear AO devices, and optical radiation spectral components diffract in the acoustic field in different parts of the AO crystal, accurate calculation of the characteristics of such devices requires knowing the distribution of the acoustic field amplitude inside the AO cell. The acoustic beam structure is affected by several factors in quasicollinear AO cells: the dimensions of the piezoelectric transducer, the geometry of acoustic wave propagation in the AO cell, acoustic anisotropy and the acoustic energy absorption along the chosen direction in the crystalline material used. In this paper, we propose a generic method to measure the acoustic beam power distribution along the direction of its propagation in the quasicollinear AO cell in the presence of ultrasound power absorption and media acoustic absorption. The measurements were carried out for the ultrasound frequency range from 72 to 176 MHz, for the case when the wave vector of the acoustic beam is directed at an angle of 1.58∘ to the [110] axis in the (11¯0) plane of the paratellurite crystal. The ultrasound attenuation coefficients were obtained for frequency interval between 87 and 176 MHz and their linear dependence on ultrasound frequency was confirmed.

Acousto-Optic Diffraction in an Ultrasonic Field of a Width-Profiled Transducer

Acousto-Optic Diffraction in an Ultrasonic Field of a Width-Profiled Transducer

Effect of ellipticity of optical eigenwaves on the enhancement of efficiency of acousto-optic Bragg diffraction. A case of optically active Pb5Ge3O11 crystals

We show that the existence of optical activity in an optical material can lead to essential enhancement of acousto-optic (AO) figure of merit. The reason is that the ellipticity of interacting optical eigenwaves approaches unity near the optical axis and so additional elasto-optic (EO) tensor components become involved in the effective EO coefficient. We demonstrate on lead germanate crystals that the increase in the efficiency of AO diffraction manifests itself for all types of AO interactions whenever the incident optical wave propagates close to the optical axis. In the particular case of diffraction in the interaction plane XZ of Pb5Ge3O11 crystals, the maximal enhancement of the AO figure of merit takes place under conditions of the isotropic diffraction of ordinary and extraordinary optical waves with a pure transverse acoustic wave (AW) polarized parallel to the Y axis (a so-called AW PT2), with the AO figure of merit increasing from zero to 7.5 × 10−17 s3/kg, and the types of anisotropic diffraction on the AWs QT1 and PT2 when the AO figure of merit increases twice (e.g., from 7.6 × 10−17 to 1.5 × 10−16 s3/kg). The maximal AO efficiency in the interaction plane XZ is reached at types I and II of the isotropic AO interactions of ordinary and extraordinary optical waves with a quasi-longitudinal AW; in these cases, the AO figure of merit increases from 6.8 × 10−15 to 12.4 × 10−15 s3/kg and from 5.6 × 10−15 to 12.4 × 10−15 s3/kg, respectively.

A new concept of acousto-optic tunable filter-based near-infrared hyperspectral imager for planetary surface exploration.

In the past two decades, near-infrared (NIR) hyperspectral imaging instruments have revolutionized our conception of planetary surfaces in terms of evolution, geology, mineralogy, and alteration processes. The cornerstone of this remote analysis technique is the synergy between imagery, giving the geomorphological context of the observations, and NIR spectroscopy whose spectral range is sensitive to the main absorption features of most of the minerals present on planetary surfaces. The development of a generation of space instrument based on Acousto-Optic Tunable Filters (AOTFs) increases the capacity of these spectrometers to be set up in a variety of space probes. The ExoCam concept, developed at Institut d'Astrophysique Spatiale and profiting from the lab's previous experience (MicrOmega onboard Phobos-Grunt, Hayabusa 2 and ExoMars), thus, proposes for the first time to do hyperspectral imagery through a wide aperture AOTF (15 × 15 mm2) in the 0.95-3.6 µm spectral range. The characterization of this instrumental concept, led on a representative breadboard built for this purpose, showed that the acousto-optic diffraction preserves the image quality up to the diffraction/resolution limit over the whole field of view. The spectral resolution (from 2 to 25 nm over the spectral range) and accuracy of the instrument are also consistent with the identification of planetary surface minerals. This paper describes the ExoCam concept and objectives, the setup of an optical breadboard representative of a space instrument based on this concept, and the results of performance characterizations realized on the breadboard.

Optimal Design of an Ultrasound Transducer for Efficient Acousto-Optic Modulation of Terahertz Radiation.

Acousto-optic (AO) interaction in the terahertz range was investigated with the use of monolithic ultrasound transducers of various widths. Sulfur hexafluoride (SF) liquefied at a temperature of about 23 °C and a pressure of 25 bar was used as a medium for AO interaction. The angular and frequency bandwidths of effective AO interaction, as well as the diffraction efficiency per 1 W of the driving electric power, were determined. For the first time, a correct comparison of the AO diffraction efficiency in SF with the use of ultrasound transducers with different widths was carried out. In the experiments performed, the highest energy efficiency of the AO modulator was achieved with a transducer with a width of 12 mm.

Acousto-Optic MultiBeam Axial Diffraction in Paratellurite

To form a multibeam radiation pattern, it is proposed to use the axial geometry of acousto-optic interaction in paratellurite. In the single frequency mode, the use of this geometry for angular scanning is characterized by a dip in the frequency response. Optimization of a multifrequency radio signal makes it possible to efficiently divide laser radiation into several beams with maintaining the fundamental advantages of axial geometry: minimum crystal size and power consumption. Keywords: acousto-optic diffraction, acousto-optic deflector, axial geometry, multifrequency mode, paratellurite.