Powerful single-frequency CO₂ laser for plasma diagnostics

A cw 240-W CO₂ laser has been developed for plasma scattering measurements. The laser oscillates only on the 10P(20) transition (10.5912-μm wavelength) at a single longitudinal as well as transverse mode with linear polarization. These properties are obtained by using an adequately long cavity with a folded beam configuration. Part of the output beam was heterodyned with a local oscillator laser to confirm the single-frequency oscillation. The short-term frequency stability was 200 kHz (7×10^-9) for an observation time of 1/15 s. The shift of the oscillating frequency due to the discharge current was 360 kHz/mA and the frequency shift due to the total gas pressure was 4.1 MHz/Torr. These frequency shifts are mostly attributable to the change of the refractive index of the laser gas.