Satoshi TANAKA, Yuzo SETOGUTI and Heihachi SATO

Department of Electrical Engineering, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, 239-8686 Japan

(Received August 10, 1999; Accepted November 10, 1999)

As a complementary scheme to a coupling-hole type laser, a walk-off ring coupling type laser is proposed to extract a donut shaped beam by shrinking the diameter of one of the stable resonator mirrors. This was successfully applied to a conventional slow axial-flow CO laser. First, finding the intensity distribution close to the Gaussian profile by using a partially transparent mirror in a hemispherical configuration for coupling, we obtain the relationship between the mirror radius and the effective transmittance. Then, using several mirrors with a diameter smaller than the Gaussian profile above instead of the partially transparent mirror, the output power with the donut shape was optimized to yield the maximum power, together with theoretical treatments. This resulted in an optimum mirror diameter of 4.2 mm, which corresponds to the optimum transmittance of 5-6% for the CO laser having the gain parameter G~0.34, the inherent loss α_i ~0.07, and the measure of partial homogeneity m=0.5. This value is exactly the same as that of the coupling-hole mirror. Some application feasibilities are also discussed.

Key words : gas lasers, CO lasers, laser resonators, optical resonators, stable resonators, laser beam shaping

satoshi@nda.ac.jp