Abstract

In the 4-5 µm range a frequency-doubled continuos-wave (cw) CO₂ laser has the potential for providing an optimal combination of spectral control and frequency stability. However, for cw systems it is difficult to achieve high efficiency of second harmonic generation (SHG) in nonlinear crystals because of low pump power. Intracavity frequency conversion is a powerful means to improve the frequency-doubling efficiency if sufficient laser power is not available. This method puts forward very strict requirements on both the nonlinear crystal and the laser. For example, it is necessary to eliminate Fresnel losses introduced by the crystal and to optimise the harmonic output coupling. Especially important is to use a nonlinear crystal of high optical quality in which residual absorption is minimised. Since nonlinear crystals in the mid-IR region do not meet these tight requirements, intracavity technique has not been applied for cw CO₂ laser radiation. Using a low-absorption AgGaSe₂ crystal we obtained for the first time to our knowledge intracavity SHG of a cw CO₂ laser. Preliminary results on the optimisation of output power at 5 µm using different schemes are presented.

© 2000 IEEE