Gaussian-beam profile shaping by acousto-optic Bragg diffraction

Abstract

We study how Gaussian laser-beam profiles can be modified into a desired form using acousto-optic Bragg diffraction. By exploiting the angular dependence of Bragg diffraction of plane waves by acoustic gratings, we demonstrate that the conversion from a Gaussian-profile beam into either a near-field or a far-field flattop profile is possible.

Two-dimensional feature extraction and beam fanning suppression using acousto-optics

“…In the above equation, we have made the assumption >> sI, where s is the ionization cross-section per quantum of light and I is the optical intensity. 16 We employ a simple technique, called the P-scan, to evaluate the nonlinearity of the photorefractive material'3. A typical far field pattern a distance of O.5m behind the sample, when a focused extraordinarily polarized Ar laser beam with a waist 50 microns is incident on a 1cm thick LiNbO3 located at the focus, is shown in Fig.…”

“…The use of AOMs for image processing has recently been explored 16 The novel feature of this technique is that optical image processing can be achieved without the use of Fourier plane spatial filters. AO modulators (AOMs) are 1-dimensional (1-D) devices in that light is diffracted in the direction of propagation of the sound.…”

Laser beam profile deformation effect during Bragg acousto-optic interaction: a non-paraxial approximation

“…[1][2][3][4] It is well known that for a Gaussian light beam, after diffraction by an ultrasonic wave in an acoustooptic medium, certain deformations can be found for the beam profiles in the diffracted light. [5][6][7][8][9][10][11] The reason for this beam deformation is due to the angle selection mechanism during the Bragg diffraction. All the developed principles and theories on this subject use the paraxial approximation, 12 viz., the paths of the diffracted light waves propagate closely along the optic axis of the acousto-optic system.…”

Notch spatial filtering with an acousto-optic modulator

“…Indeed, the spatial transfer function for an AO modulator working in the Bragg regime that shows the spatial-frequency selectivity of both the diffracted and the undiffracted orders has recently been derived and studied. [7][8][9][10][11] In short, under certain conditions, the undiffracted order has the characteristics of spatial high-pass filtering, while the transfer function for the diffracted order shows low-pass characteristics. To develop more and diversified spatial-filtering operations, techniques to compute spatial transfer functions under a variety of physical situations-such as different nominal angles of optical incidence, the utilization of different diffracted orders at the output, etc.-are needed.…”