Abstract
The use of an Yb:YAG thin-slab architecture for amplification of a radially polarised beam at 1030 nm is investigated and shown to be a promising route for power scaling. The detrimental impact of the Gouy phase shift on radial polarisation purity is considered and a simple scheme for effective phase shift management to restore polarisation purity is presented. Preliminary experiments based on a double-pass amplifier configuration yielded an output beam with a high radial polarisation extinction ratio of 15 dB and no degradation in polarisation purity despite the non- axial symmetry of amplifier gain medium. At 50 W of launched pump power a small-signal gain of 7.5 dB was obtained for a 25 mW input, whilst 4.4 dB gain was obtained for a 1.45 W input. The prospects for further power scaling are discussed.
Highlights
Cylindrical vector (CV) beams have unique characteristics whereby the polarisation state across the beam cross-section is not uniform, as with linear or circularly polarised light, but forms an axially symmetric distribution
And azimuthally polarised beams form an interesting subset of CV beams, where the polarisation direction is orientated in the radial and tangential directions, respectively
It has been shown that cutting efficiency can be 1.5-2 times higher using radial polarisation rather than circular polarisation [4], and drilling can be 1.5–4 times more efficient with azimuthal polarisation compared to linear and circular polarisation [5]
Summary
Cylindrical vector (CV) beams have unique characteristics whereby the polarisation state across the beam cross-section is not uniform, as with linear or circularly polarised light, but forms an axially symmetric distribution. Extracavity techniques typically convert more traditional polarisation states, such as linear or circular polarisation, into radial or azimuthal polarisation This can be achieved interferometrically, through the combination of orthogonal linearly polarised HG01 and HG10 beams [12]. A spatially variable retardation plate can be used to convert linear polarisation to radial or azimuthal polarisation [13] To realise their potential within material processing and other applications, CV beams must be produced with sufficient power. Amplification in a slab is simpler than in a thin-disc, which due to the very short interaction length requires a complex multi-pass arrangement to achieve an appreciable gain These benefits have allowed slab amplifiers to produce 400 W of nearly diffraction limited output power [19], and 1.1 kW of multimode output power [20].
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