Multiple line and polarization control in a far infrared laser with a compound grating resonator

Operating principles and the efficacy of two types of coupled laser resonator are described and their experimental verification presented: a compound mirror-grating-mirror resonator (MGM), and a mirror-grating-grating resonator (MGG). The coupling for both resonators is through the zero-order diffraction of the resonator's primary grating. The coupling mechanism makes it possible to obtain a particular wavelength and polarization from the resonators. Since the phase change of the radiation diffracted into both first order and zero order is different for the radiation polarized linearly parallel and linearly perpendicular to the direction of the grating lines, a different effective length of the secondary cavity exists for the two polarizations. In the case of the MGM resonator, the coupling is used to control the polarization properties of a single laser line. For the MGG resonator, the coupling is used so that two distinct laser lines can lase simultaneously. The MGG resonator also has a degree of control of the relative polarization of the two lines. The resonators are used to control the degree of the laser output coupling, output radiation polarization, and resonator bandwidth. The resonators were used for interaction studies between four pairs of water vapor lines (26.60-47.47, 26.60-47.70, 27.97-47.47, and 27.97-47.70, microm).