Power Coupling trom a C0(2) Laser by a Rotatable Reflector.
A rotatable reflector placed in the optical cavity of a laser provides a convenient practical tool for adjusting the cavity Q. It is, therefore, useful for the optimization of the power output in laser systems. In Q switched CO2 lasers, it may be used for designing an oscillator that operates at a large number of vibrational rotational transitions. The power saturation considerations show that a CO2 laser consisting of such an oscillator followed by a series of amplifiers is desirable for obtaining large power output. Also, the present analysis is useful in estimating the tolerance in setting the Brewster angle in any laser system. The method of power coupling consists of utilizing totally reflecting cavity mirrors and coupling-out the power via the rotatable plate placed in the resonator. As the plate is set at different angles, the effective losses (due to various reflections) introduced by it change; and hence the power output changes. The rotatable plate actually functions as a variable reflectivity coupling out mirror. Figure 1 shows a laser cavity having 100% reflecting mirrors, a Brewsterized laser medium, and a rotatable plate capable of rotating in such a manner that at its Brewster angle it introduces minimum losses to the laser oscillations polarized by the Brewsterized laser tube. The reflection coefficient, R, at a surface of the rotatable plate kept at an angle of incidence, ø, is given by,