Radially-polarised beams are attracting growing interest owing to their unique properties and numerous applications. Power-scaling whilst preserving the polarisation-purity of radially-polarised beams is challenging, with efforts predominantly focused on cylindrically-symmetric systems.
We explore an alternative strategy for power-scaling radially-polarised beams using a thin-slab amplifier geometry, which, to the best of our knowledge, has not been previously investigated. We show that very high radial polarisation-purity can be maintained in an architecture that can be operated at high powers.
A radially-polarised seed-source was constructed using an Yb:YAG rod in a plane-parallel configuration, pumped by a capillary delivery-fiber which provided effective overlap with the LG01 mode. By tuning the cavity length and utilising thermally-induced birefringence, a robust multi-Watt LG01 mode was generated with an excellent radial polarisation-purity of 15dB and good beam quality M2=2.2.
The Yb:YAG slab was pumped by a diode-bar producing a highly-elongated inversion region. The seed was amplified in a double-pass configuration, using a cylindrical lens to spatially-match the inversion. The output beam was re-collimated by the cylindrical lens, and compensation for the Gouy phase-shift was made using a half-waveplate.
At 50W of incident pump power we obtained a small-signal gain of 7.5dB and a power gain of 4.5dB for 1.45W seed power. At maximum pump power the radial polarisation-purity was maintained at 15dB, and the beam quality only degraded slightly to M2=2.3. Further optimisation of slab design and pump geometry will be discussed in addition to power-scaling the system to higher output powers necessary for a range of applications.
Callum R. Smith, Stephen J. Beecher, Jacob I. Mackenzie, and W. Andrew Clarkson, "Radially-polarised beam amplification in an Yb:YAG thin-slab architecture (Conference Presentation)," Proc. SPIE 10082, Solid State Lasers XXVI: Technology and Devices, 1008204 (Presented at SPIE LASE: January 30, 2017; Published: 21 April 2017); https://doi.org/10.1117/12.2256298.5383482318001.
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