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. We analyze how a nonradially symmetric pump distribution induces a nonradially symmetric stress map. This manifests itself as nonradially symmetric birefringence, and as depolarization to radially/azimuthally polarized beams (or as deterioration in birefringence compensated linearly polarized lasers). Here we analytically describe the birefringence terms of a nonradially symmetric strain map. The model results are supported by radial-depolarization measurements in our 2 kW Nd:YAG pump chambers. For the current level of depolarization, beam quality degradation per rod is DeltaM(2)=4 because of bifocusing alone. The degradation per rod can be reduced substantially by improving pump uniformity.
Lumer
Yaakov
Y
Non-Linear Optics Group, Soreq Nuclear Research Center, Yavne 81800, Israel. lumer@soreq.gov.il
Moshe
Inon
I
Horovitz
Zvika
Z
Jackel
Steven
S
Machavariani
Galina
G
Meir
Avi
A