<title>Development of red internal mirror He-Ne lasers with near-critical concave-convex stable resonators</title>

Abstract

Basic properties of the concave-convex stable resonator (CCSR) with cavity parameter g1g2 near to 1 are discussed in the infinite aperture approximation. The field distributions and diffraction losses of the low order transverse modes of related resonators with finite aperture are analyzed numerically. The stability of the output power of the lasers with CCSR are studied experimentally. We have made a total of 120 red internal mirror He-Ne lasers with CCSR (g1g2 >= 0.90) whose cavity lengths are approximately 63 cm and the effective lengths of discharge tubes are about 52 cm. Most of the lasers operate with TEM00 stably, and the highest output power is 30 mw. The laser beam waist lies outside the resonator at a distance of 1.0 m from the concave mirror, and the beam divergence is 0.45 mrad. For the TEM00 lasers operate normally, the misalignment angle of the resonator mirrors must be less than 10-5 mrad. The following facts are of particular value. (1) When the resonant frequency spacing between two successive transverse modes of a CCSR (Delta) (nu) is so small that its effect on the competition among transverse modes in the lasers with the CCSR can be negligible, we call such a CCSR near critical CCSR (NCSR). It is observed that even if the round trip total loss (including the transmission loss and so on) of TEM00 is only about 0.2 round trip small signal gain of the laser, and the round trip diffraction loss of TEM00 is only about 0.001, still the laser with the NCSR operate with pure TEM00 stably. It is clear that the mode competition in a laser with NCSR is extraordinarily favorable for TEM00$. (2 While the TEM00 lasers operate normally, the center frequency of every longitudinal mode is stable, its drift per hour is less than 0.1 longitudinal mode spacing (approximately equals 2.4 X 107 Hz). (3) The superradiant transition at 3.39 micrometers is suppressed.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.