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High average power second harmonic generation in air
Martynas Beresna1, Peter G.Kazansky1, Yuri Svirko2, Martynas Barkauskas3, and Romas Danielius3
1. Optoelectronics Research Centre, University of Southampton, UK
2. Department of Physics and Mathematics, University of Joensuu, Joensuu FI-80101, Finland
3. Light Conversion Ltd., Vilnius, LT-10223, Lithuania
Abstract
We demonstrate second harmonic vortex generation in atmospheric pressure air using tightly focused femtosecond laser beam. The circularly polarized ring-shaped beam of the second harmonic is generated in the air by fundamental beam of the same circular polarization, while the linear polarized beam produces two-lobe beam at the second harmonic frequency. The achieved normalized conversion efficiency and average second harmonic power are two orders of magnitude higher compared to those previously reported and can be increased up to 20 times by external gas flow. We demonstrate that the frequency doubling originates from the gradient of photoexcited free electrons created by pondermotive force.
Applied Physics Letters (2009) Vol.95 pp.121502
doi: 10.1063/1.3232235
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Copyright University of Southampton 2006