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

Malcolm W. McGeoch

doi:10.1117/12.145205

6 June 1993 Efficient generation at 4.8 μm by doubling of mode-locked CO₂ laser radiation

Malcolm W. McGeoch

Proceedings Volume 1871, Intense Laser Beams and Applications; (1993) https://doi.org/10.1117/12.145205
Event: OE/LASE'93: Optics, Electro-Optics, and Laser Applications in Scienceand Engineering, 1993, Los Angeles, CA, United States

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.

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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); https://doi.org/10.1117/12.145205

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KEYWORDS

Crystals

Silver selenogallate

Mode locking

Carbon dioxide lasers

Laser crystals

Modulation

Coating

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