Takeshi YASUI,¹ Tsutomu ARAKI^2,* and Norihito SUZUKI³

¹Department of Mechanical Engineering, University of Tokushima, Jousanjima, Tokushima, 770 Japan, ²Department of Systems and Human Science, Graduate School of Engineering Science, Osaka University, Toyonaka, 560 Japan, ³Department of Precision Engineering, Osaka Electro Communication University, Neyagawa, 572 Japan

(Received September 17, 1997; Accepted October 22, 1997)

A high-power, unmodulated frequency standard laser light with low running cost is a powerful tool for industrial measurement involving laser calibration and interferometry in length and shape. To obtain such a laser light, we developed an intermittent frequency offset locked laser (IFOL laser). This laser system, composed of an iodine stabilized He-Ne laser (I₂SL) and a high-powered symmetric three-mode He-Ne laser (HP-3ML, optical output=5 mW), provides two stabilization operational modes: (1) independent mode (I-mode) and (2) slave mode (S-mode). Utilizing the frequency pulling effect, HP-3ML is stabilized at the condition of symmetric three-mode oscillation, and a 3 mW single-mode light with frequency instability of 10^-12 is obtained (I-mode). When the optical frequency deviates from the allowed limit during I-mode, HP-3ML is temporarily offset-locked to I₂SL (S-mode) with frequency resettability of 10^-10 and frequency instability of 10^-12. After completion of the drift reset in S-mode, HP-3ML is stabilized in I-mode again, and then I₂SL is turned off. In a typical case of allowed drift in ±1 MHz, repetitive operation of I-mode for 10 days and S-mode for 5 min was satisfactory. Such an intermittent operation reduces the working time of I₂SL dramatically, resulting in low running cost that enables long-term use in industrial measurement.

Key words : frequency stabilized He-Ne laser, frequency standard laser, iodine stabilized He-Ne laser, single-mode laser, frequency offset lock, frequency pulling, high accuracy

*araki@me.es.osaka-u.ac.jp