Enhancement of modal feedback in unstable resonators using mirrors with a phase step

Far-field intensity distribution of a beam generated by a resonator with a phase-unifying mirror

The far-field intensity distribution (FFID) of a beam generated by a phase-unifying mirror resonator was investigated based on scalar diffraction theory. Attention was paid to the parameters, such as obscuration ratio and reflectivity of the phase-unifying mirror, that determine the FFID. All analyses were limited to the TEM00 fundamental mode.

Effect of phase imperfections on high-order mode selection with intracavity phase elements

To obtain a laser beam containing only one pure high-order transverse mode, one can insert a binary phase element (BPE) into a laser resonator. I investigate the effect of deviations in the discontinuous height of the BPE on the selection of high-order Hermite-Gaussian (HG) modes. Both matrix-diagonalization and numerical Fox-Li calculations to obtain the loss per pass and beam propagation factor of the output beam obtained with a deviated BPE are performed. Experimental results obtained with a Nd:YAG laser operated with HG (1,0) and HG (1,1) transverse modes are presented and compared with theoretical modes.

Design of polarization-selective diffractive phase elements in a laser cavity

We report a new design for a polarization-selective laser cavity with birefringent diffractive phase elements. This laser cavity can create two modes with different polarizations and profiles launched separately from two end mirrors. The numerical simulation results show that the constructed laser cavity can successfully generate two orthogonal polarization modes with a uniform circular shaped pattern output from one end mirror and a uniform square-shaped pattern output from another end mirror.

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.

Beam-divergence control of excimers with plane-parallel Gaussian cavities

Plane-parallel cavities with Gaussian-reflectivity-profile mirrors as full reflectors were applied to a XeCl laser, and the near- and the far-field characteristics of the laser radiation were analyzed. It is shown that excimer lasers fitted with plane-parallel Gaussian cavities deliver laser radiation with a beam-quality factor M(2) that is more than 50% smaller than that of laser beams delivered by conventional plane-parallel cavities. The effect of the Gaussian mirror spot size on M(2) was also investigated, and it is shown that the narrowing of the Gaussian mirror spot size reduces the beam-quality-factor value.

Phase shift of stepwise reflectivity profile mirrors

The effects of phase shifts in laser beams transmitted by output couplers with a stepwise reflectivity profile have been experimentally investigated with a XeCl laser. It is shown that the phase distortions of the cavity output coupler affect significantly the propagation properties of the output laser beam but do not affect the output beam energy and pulse width.

High modal discrimination in a Nd:YAG laser resonator with internal phase gratings

A unique laser resonator containing an internal phase grating and a diffractive mode-selecting mirror provides high modal discrimination in a Nd:YAG laser cavity. Single-spatial-mode lasers with high Fresnel numbers are possible, with negligible loss to the fundamental mode.