期刊
APPLIED PHYSICS LETTERS
卷 95, 期 12, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.3232235
关键词
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资金
- Physical Sciences Research Council (EPSRC)
- Academy of Finland [131165]
- Academy of Finland (AKA) [131165, 131165] Funding Source: Academy of Finland (AKA)
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. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3232235]
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