Acousto-optic Diffraction Efficiency Research Articles

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.

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

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.

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.

任意偏振光保偏的声光衍射效率增强系统的研究

任意偏振光保偏的声光衍射效率增强系统的研究

Shear acoustic wave attenuation influence on acousto-optic diffraction in tellurium dioxide crystal.

The slow shear acoustic wave attenuation in a tellurium dioxide crystal (11¯0) plane is examined. The measurements were carried out for two crystal cutoff angles: 7° and 10.5° from the [110] axis. The ultrasound attenuation was examined in the frequency range of 80 to 300 MHz by the acousto-optic (AO) method. The attenuation coefficients were determined for both acoustic wave propagation directions for the frequency range of 200 to 300 MHz. The influence of ultrasound attenuation on the AO cell transmission functions was examined for the 10.5° AO cell both theoretically and experimentally. It is shown that acoustic wave absorption affects mainly the AO diffraction efficiency. The attenuation influence on the AO cell transmission function shape and its half-width is not significant.

Spin-to-orbit conversion at acousto-optic diffraction of light: conservation of optical angular momentum

Acousto-optic diffraction of light in optically active cubic crystals is analyzed from the viewpoint of conservation of optical angular momentum. It is shown that the availability of angular momentum in the diffracted optical beam can be necessarily inferred from the requirements of angular momentum conservation law. As follows from our analysis, a circularly polarized diffracted wave should bear an orbital angular momentum. The efficiency of the spin-to-orbit momentum conversion is governed by the efficiency of acousto-optic diffraction.

Spatial anisotropy of the acousto-optical efficiency in lithium niobate crystals

We report the spatial anisotropy of the acousto-optic (AO) figure of merit M2 in LiNbO3 crystals. The analysis is based on the indicative surfaces being calculated for several geometries of the AO diffraction. Basing on these results the most efficient geometries of AO cells made of LiNbO3 crystals are determined. It is revealed that the cells made of certain nondirect crystal cuts provide several times better AO diffraction efficiency comparing to the traditional ones, i.e., made of direct cuts of LiNbO3. The obtained results present considerable practical interest since may be useful in a designing of highly efficient AO cells made of LiNbO3 crystals. The methodology developed in the present work may be applied to other crystal materials as well.

Acousto-Optic Interaction in Cells with Wedge-Shaped Transducers Excited at High Harmonics

Diffraction of light in a non-homogeneous acoustic field produced by a wedge-shaped piezoelectric transducer is studied theoretically. Electrical, acoustic and acousto-optic characteristics of cells with the wedge-shaped transducers are calculated. Most attention is focused on special features of these cells operation at transducer's third harmonic frequency. It is shown that the acoustic field has a complicated amplitude and phase structure which varies with ultrasound frequency. The dependence of the acousto-optic diffraction efficiency on the acoustic wave amplitude and the phase mismatch is studied. It is established that the diffraction efficiency can approach 100% despite a noticeable phase mismatch. Optimal values of acoustic power and light incidence angles are found. It is revealed that due to the wedge-like form of the transducer the frequency band at the third harmonic can be several times increased with retaining a high value of the electric-to-acoustic power conversion.

Acoustooptic cells with wedge-shaped piezoelectric transducers excited at high-order harmonics

Light diffraction in a nonuniform acoustic field induced by a wedge-shaped piezoelectric transducer is theoretically studied. Electric, acoustic, and acoustooptic characteristics of cells with such transducers are calculated. The emphasis is on the features of cell operation in the case when a piezoelectric plate is excited at the third harmonic. The acoustic field is shown to possess a complex amplitude and phase structure varying with the ultrasound frequency. The efficiency of acoustooptic diffraction depending on the acoustic wave amplitude and phase mismatch is studied. It is established that the efficiency of the Bragg diffraction can approach 100% despite a noticeable phase mismatch. Optimal values for the ultrasound power and angles of light incidence onan acoustooptic cell are found.

Acoustooptic Diffraction in Borate Crystals

The efficiency of acoustooptic (AO) diffraction in a-BaB2O4 and Li2B4O7 crystals is studied experimentally. The crystals are shown to be quite good AO materials. The efficiency of AO diffraction in a-BaB2O4 reaches h=30% at the electric signal power of P=0.7W for the transverse acoustic wave and 15% at the power of P=0.56W for the longitudinal wave. The same parameter for Li2B4O7 reaches h=21% at P=0,81W for the longitudinal acoustic wave.

Cascade acousto-optic frequency shift of light

A new method for drastically shifting the carrier frequency of light based on the acousto-optic (AO) cascade diffraction effect is described and investigated. The method is based on the peculiarities of anisotropic diffraction in anisotropic media and allows separation of the different diffracted beams in the multi-stage diffraction process. The feasibility of the novel method is experimentally verified by using a common TeO2 monocrystal as the AO medium and standard optical units. A prototype comprising a five-stage cascade process with a total frequency shift of 400 MHz was built and tested with an overall AO diffraction efficiency of 40%. Issues for improving this efficiency are discussed.

Efficient acousto-optic Q switching of Er:YSGG lasers at 279-µm wavelength

A flash-lamp-pumped Er:Cr:YSGG laser at 2.79-microm wavelength has been acousto-optically Q switched. The Q-switched pulse energy and duration depend on pump pulse level and relative Q-switching time. Limits of single-pulse operation with the given acousto-optic diffraction efficiency have been determined. Resonator length, position of the Q switch, and output mirror reflectivity have been varied to obtain high pulse energy and the shortest pulse duration in the TEM00 transverse laser mode. A maximum single-pulse energy of 27 mJ and a minimum pulse duration of 120 ns were obtained with an output mirror reflectivity of approximately 25%. The highest Q-switched single-pulse energy amounted to 52% of the free-running, fundamental mode output pulse energy.

Performance of an acousto-optic Bragg cell under ion microbeam irradiation

An acousto-optic (AO) deflector composed of PbMoO 4 was exposed to 4 MeV protons while operating under Bragg angle conditions. An ion beam in air of 1 mm width was directed normal to the crystal face and laser beam. Between exposures, the approximately 13 mm × 8.5 mm AO deflector was mechanically translated in two dimensions in front of the fixed ion beam. The AO diffraction efficiency was mapped and was observed to change as a function of ion beam location and dose rate. These effects are attributed to the induced change in the temperature distribution of the crystal, which changed the sonic velocity and refractive index. Similar effects were observed when the ion beam was directed at the acoustic transducer.

Growth and characterization of mercurous halide crystals: mercurous bromide system

Mercurous bromide single crystals were grown by the physical vapor transport method in a sealed quartz tube. Growth rates were measured for crystals growing in different orientations. Experimental data followed the equation l t = l ∞− A exp(− t/ τ), where l t is the length of the crystal at any time t, l ∞ is the final statio nary length, and A and τ are constants. Crystals growing in 〈001〉 orientation had much higher velocity than crystals growing in 〈110〉 orientation. Large crystals were grown in 〈110〉 orientation by using preoriented seeds, an orientation needed for acousto-optic devices. The optical quality of mercurous bromide crystals was evaluated by fabricating a 5 cm long crystals. The acoustic velocity measurement data showed that the value for the slow shear velocity propagating along 〈110〉 is 2.73 × 10 4 cm/s, consistent with the values reported earlier. This translates with a high value of photelastic coefficient, into a high acousto-optic diffraction efficiency; 2600 with respect to quartz. These results showed that mercurous bromide has potential as an efficient Bragg cell with a delay time greater than 200 μs in a compact package.

Acoustooptic interaction at 520 MHz in proton-exchanged Y-lithium niobate waveguides

Experimental results are reported on acoustooptic interaction at 520 MHz in proton-exchange waveguides in Y-lithium niobate. The acoustooptic diffraction efficiency for an electrical input of 300 mW is 39% in proton-exchanged devices as compared to 22% in titanium-indiffused ones. The dynamic range observed in proton-exchanged and Ti-indiffused acoustooptic devices is 22 and 25 dB, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Guided-wave acousto-optic interaction in proton-exchanged Y-cut LiNbO3

We report for the first time results for acousto-optic interaction in proton-exchange waveguides in Y-LiNbO3. The value of acousto-optic diffraction efficiency was as high as 72% for an electrical input power of 540 mW at 425 MHz.