Acousto-optic tunable filter using double interaction for sidelobe reduction

Abstract

We present a bifrequency acousto-optic tunable filter (AOTF) for applications using polychromatic laser beams. The acousto-optic device is based on two successive anisotropic interactions in paratellurite: the first takes place with an acoustic shear wave tilted at 10 degrees from the [110] axis, while the latter is provided by the acoustic shear wave propagating collinear to the [110] axis. It is then demonstrated that the sidelobes of the impulse response to optical wavelengths of such a bifrequency AOTF are greatly reduced. General expressions of operating frequencies, spectral bandwidths, and acoustic powers are derived. Numerical computations have been drawn for paratellurite. The bifrequency AOTF has been tested using a multiline beam radiated by an argon laser. According to the spectral power distribution of this polychromatic laser beam, the most critical configurations of wavelength filtration have been considered. Experimental results confirm the theoretical predictions.

Multi-wavelength off-axis digital holographic microscopy with broadly tunable low-coherent sources: theory, performance and limitations

“…is a Gaussian function [7,11], the constant C is calculated as C = (4 ln 2)/π ≈ 0.88. If we choose sinc 2 -function, which is commonly used to describe the transmission function of AOTF [36,38,46,47], C is also approximately equal to 0.88 (see derivation in appendix A).…”

“…AOTF can operate in multifrequency mode which also enables several bands with tunable central wavelengths [5,23,24] and has options to increase the bandwidth and control the shape of the transmission function by driving signal modulation [34][35][36]. Although some AOTFs used for MDHM provided rather low coherence length that limited the informative image area [11,24], it may be significantly increased by proper design of the acousto-optic (AO) interaction geometry (directions of wavevectors for light and ultrasound) and the piezotransducer [37][38][39], e.g. the bandwidth can be less than 0.2 nm in quasi-collinear AOTFs [34].…”

Acousto-optic wide band optical low-frequency shifter

“…The ultrasonic wave exhibits a walk-off angle of energy flow ψθ a [21], i.e., the angle between the phase velocity Vθ a and the group velocity V g θ a :…”

“…Acousto-optic frequency shifters (AOFS) are key components often used in a number of recent applications, including optical heterodyning and interferometry as, for example, laser Doppler velocimetry and vibrometry [1][2][3], fringe projection [4,5], optical coherence tomography [6][7][8][9], holography [10,11], spectroscopy [12,13], optical communication [14], and four-wave mixing microscopy [15]. Various optical architectures have been proposed in the literature in order to obtain low-frequency or high-frequency shifts [16][17][18][19][20][21][22].…”

Double-Frequency-Shift Acousto-Optic Modulator with Controllable Pulse Pair Frequency Difference

“…Gazalet et al [20] designed a frequency shifter with double TeO 2 crystals and a large deflection angle, which can obtain a single frequency of ± 12 MHz without changing the output angle of the frequency-shifted order. Kastelik et al [21] loaded different RF signals into the same crystal to achieve the difference frequency output of diffraction light. Li et al [22] completed the small-scale phase-modulation of incident light by using a series structure of two polarization-insensitive AOMs.…”