The red side (lower-frequency) mode of a two-mode stabilized 633-nm He–Ne laser has been locked to the hyperfine structure of the <i>P</i>() line of <sup>127</sup>I<sub>2</sub> by means of frequency modulation spectroscopy enhanced by an external optical cavity. Both the red side and blue side (higher-frequency) modes of the laser exhibit a frequency stability of 2.3 × 10<sup>−11</sup> τ<sup>−1/2</sup>. In addition, the frequency fluctuations of the blue side mode are detected by a Fabry–Perot cavity and compensated through an acousto-optic frequency shifter. The short-term stability of better than 3 × 10<sup>−11</sup> is attained for integration times of between 2 × 10<sup>−3</sup> and 2 × 10<sup>−1</sup> s.
© 1998 Optical Society of America
Fumio Murakami, Masahiko Tsukuda, and Tatehisa Ohta, "Frequency Stability Improvement of a Two-Mode Stabilized 633-nm He-Ne Laser," Appl. Opt. 37, 526-529 (1998)