CO2-LASER FOR LIDAR APPLICATIONS, PRODUCING 2 NARROWLY SPACED INDEPENDENTLY WAVELENGTH-SELECTABLE Q-SWITCHED OUTPUT PULSES

In this research directed toward using lidar methods for mapping concentrations of a variety of hazardous gases and vapors in an indoor workplace, a need was identified for a CO2 laser that would meet certain special requirements, including an ability to produce 50-100-ns FWHM pulses in pulse pairs having interpulse spacings of 5-100-mu-s with each pulse of the pair being independently wavelength selectable. A laser was constructed with a low-pressure CO2 amplifier section because of CO2's long upper lasing level lifetime (> 60-mu-s). This permitted the Q switching of two output pulses from a single laser amplifier electrical transverse discharge pulse, while allowing several microseconds for wavelength changing between pulses. An intracavity beam telescope was employed to use the amplifier discharge cavity cross section efficiently with the small CdTe Q-switch crystals available. A 1200-Hz oscillating grating with a high-resolution grating position sensor was used to change and reprogram wavelengths rapidly. Programming of wavelengths was accomplished by selecting appropriate delay times from the grating position reference signal for triggering the laser amplifier and the Q switch. Most of the basic performance goals of the device were achieved in the laboratory prototype.