Efficient frequency-doubled single-frequency Nd:YAG laser

The design and operation of an efficient stable frequency-doubled single-frequency Nd :YAG laser providing a unidirectional harmonic output is discussed. Efficient resonant cavity designs utilizing the Nd:YAG rod as an internal focusing element were used to provide adequate TEM00-mode volume in the rod and a small beam waist at the nonlinear crystal (Ba2NaNb5O15) for optimum intracavity second-harmonic generation (SHG). Various two-component low-loss intracavity mode filters were investigated and a double Fabry-Perot (F-P) fused-quartz etalon arrangement devised to obtain single-frequency operation with relative ease. The unidirectional harmonic output geometry uses a 45° mirror which favorss-polarized laser oscillations at 1.06 μm and very effectively transmits the second harmonicp-polarized radiation. Other component designs include short-radius mirror coatings highly reflective at 1.06 and 0.53 μm, and antireflection (AR) coatings on the nonlinear crystal for both wavelengths. Relative phase differences between the fundamental and harmonic radiations are uncritical and compensable by adjusting the nonlinear crystal temperature. The techniques adopted have proven adequate and stable unidirectional single-frequency power outputs of 0.3-0.5 W were obtained consistently from a 5- by 50-mm Nd:YAG rod pumped effectively with 850 W with a tungsten-iodine lamp in a spherical pump cavity.