CO2 Laser Frequency Doubling
Abstract
This work addresses the possibility of a high average power coherent light source in the mid-infrared, specifically 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 modelocking. The intensity for efficient conversion in typical available lengths of doubling material is at a minimum 20 MW sq.cm. However, the most efficient CO2 lasers operate with a pulse duration of at least 1 microsec, the characteristic time for energy transfer from N2 to CO2 at 1 atmosphere. Without modulation a fluence of at least 20 J sq.cm 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 J sq.cm range that typifies the surface damage threshold of available materials. One important unknown was the effect on damage threshold of a modulated versus an unmodulated pulse. Was the threshold dependent on peak intensity, or fluence? Other questions related to the specific material AgGaSe2, silver gallium selenide, chosen for this work. What was the quality of the second harmonic beam; what was the effective nonlinear coefficient; what was the temperature dependence of the phase-matching; and what was its thermal conductivity (to remove absorbed heat in an average power situation)?
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 24, 1992
- Accession Number
- ADA251060