Comparison of GaAs and CdTe crystals for high-frequency intracavity coupling modulation of CO2lasers

High-frequency intracavity coupling modulation of the CO2laser has recently attracted considerable interest as an efficient means of achieving wide-bandwidth modulation with low modulator drive power. In the present investigation, intracavity coupling modulation was achieved at 1 GHz. Both GaAs and CdTe crystals were investigated and an optical beat method was used to explore the operational characteristics of such systems without having to go to the expense and trouble of high-speed detectors. The modulation efficiencies at the 1-GHz modulation rate were 0.5 and 1 percent for GaAs and CdTe electrooptic modulators, respectively. Modulator crystal characteristics such as electrical resistivity, radiation absorption, crystal uniformity, etc., which are of critical importance for intracavity modulation, were also measured for both crystals.