Methods for optimizing the beam shape in a focused coherent optical system

Transformation of gaussian to coherent uniform beams by inverse-gaussian transmittive filters

Several plano-convex aluminum thin films, ~30 nm thick in the center and ~2 mm in diameter, were deposited on microscope cover slides to function as inverse-Gaussian transmittive filters. By placing one of these filters in front of the Gaussian He-Ne laser, we can modify the beam intensity profile in the downstream direction. To yield a uniform beam, the position of the filter must be aligned in the transverse plane for maximum intensity at the output of the filter. These filters are easy to fabricate and are inexpensive. Most important, they can help produce collimated phase-coherent uniform beams, which are useful in high-precision fringe-analysis techniques.

Gaussian-beam profile shaping by acousto-optic Bragg diffraction

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.

Acoustooptic 2-D profile shaping of a Gaussian laser beam

Acoustooptic 2-D profile shaping of a Gaussian laser beam has been achieved by two plane ultrasonic waves progressing in orthogonal directions. The spot size W of the Gaussian laser beam must be considerable less than the wavelength lambda of the ultrasonic wave at the acoustooptic interaction region. The ultrasonic cell is dealt with as a Raman-Nath 2-D phase grating but serves as a 2-D beam deflector in time for the interaction scheme of interest. The wave front of the Gaussian laser beam must be almost plane in the interaction region. The profile shaping condition is 0.15 < or = (W/lambda) < or = 0.30 only when the Raman-Nath parameter dependent on the ultrasonic power has values between v = 1.0 and 2.0.