Thermally induced birefringence in nonsymmetrically pumped laser rods and its implications for attainment of good beam quality in high-power, radially polarized lasers.

The ability to generate and then amplify radially polarized light opens up the possibility of achieving very high-power, near diffraction-limited beams from rod-based solid-state lasers. Residual bifocusing rapidly degrades beam quality. Residual bifocusing results from nonradially symmetric pump distributions.

Efficient formation of a high-quality beam from a pure high-order Hermite-Gaussian mode.

We present a relatively simple method for efficiently transforming a single high-order mode into a nearly Gaussian beam of much higher quality. The method is based on dividing the mode into equal parts that are then combined coherently. We illustrate the method by transforming a Hermite-Gaussian (1, 0) mode with M(x)(2)=3 into a nearly Gaussian beam with M(x)(2)=1.

Spatially variable retardation plate for beam brightness enhancement in a high-power laser.

We present a simple and robust method for brightness enhancement, efficiently transforming a radially polarized LG (0,1)(*) mode into a nearly Gaussian beam of much higher quality. We use for this a spatially variable retardation plate and a spatial filter. The analysis shows that the transformation yields an increase in brightness by a factor of 3.

Efficient extracavity generation of radially and azimuthally polarized beams.

We demonstrate an efficient transformation of a linearly polarized Gaussian beam to a radially or an azimuthally polarized doughnut (0,1)* Laguerre-Gaussian beam of high purity. We use a spatially variable retardation plate, composed of eight sectors of a lambda/2 retardation plate, to transform a linear polarization distribution to radial/azimuthal distribution. We transformed an Nd:YAG Gaussian beam with M(2)=1.

Birefringence-induced bifocusing for selection of radially or azimuthally polarized laser modes.

We develop a round-trip matrix diagonalization method for quantitative description of selection of radially or azimuthally polarized beams by birefringence-induced bifocusing in a simple laser resonator. We employ different focusing between radially and tangentially polarized light in thermally stressed laser rods to obtain low-loss stable oscillation in a radially polarized Laguerre-Gaussian, LG(0,1)*, mode. We derive a free-space propagator for the radially and azimuthally polarized LG(0,1)* modes and explain basic principles of mode selection by use of a round-trip matrix diagonalization method.