Efficient generation at 4.8 um by doubling of mode-locked CO2 laser radiation

Malcolm W. McGeoch

doi:10.1117/12.145205

Abstract

This work addresses the possibility of a high average power coherent light source in the 4.8 micrometers atmospheric window. The approach is to frequency-double the 9.55 micrometers CO₂ laser line, yielding 4.775 micrometers . In order to achieve efficient conversion, the intensity of the laser is increased by intracavity resonant modulation, or 'mode-locking'. Efficient conversion in available lengths of doubling material requires an intensity of at least 20 MWcm^-2. However, the most efficient CO₂ lasers operate with a pulse duration of at least 1 microsecond(s) ec, the characteristic time for energy transfer from N₂ to CO₂ at 1 atmosphere. Without modulation a fluence of at least 20 Jcm^-2 would therefore be needed for high overall system efficiency. With modulation at a 1:10 or better mark-to-space ratio, this fluence is reduced to the 2 Jcm^-2 range that typifies the surface damage threshold of available materials. The doubling material chosen for this work was AgGaSe₂, silver gallium selenide. A relatively long crystal (35 mm) was used in Type 1 phase-matching. A mode-locked pulse train was generated using a TEA CO₂ laser pumped for a duration of 3 microsecond(s) ec, containing 1 nsec pulses spaced by 40 nsec. The 9.55 micrometers line was selected either by injection or by the use of an intracavity grating.

Citation Download Citation

Malcolm W. McGeoch, Malcolm W. McGeoch, } "Efficient generation at 4.8 μm by doubling of mode-locked CO₂ laser radiation", Proc. SPIE 1871, Intense Laser Beams and Applications, (6 June 1993); doi: 10.1117/12.145205; https://doi.org/10.1117/12.145205

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