Laser mode selection by internal reflection prisms.

Internal reflection prisms were used to produce a narrow angular range of high reflectivity within a laser cavity. The selectivity was obtained from the sharp angular variation of internal reflectivity near the critical angle. Angular mode selection of a Nd: glass normal laser was achieved by this critical internal reflection (CIR) technique. Two-dimensional angular mode selection was observed with two orthogonal Lummer-Gehrcke plates within the laser cavity.