Frequency Stabilization of Ar+ Lasers by Saturated Absorption in External 127I2 Cells (at 582 THz)

The frequency of commercial Ar+ lasers at 582 THz was stabilized by an external device mainly consisting of a 127I2 cell, two photodetectors, an electronic divider, and a conventional servo loop, using the 3f locking technique. The symmetry of the 3f signals was tested by two methods. In the neighborhood of the central zero crossing at separations of up to ±300 kHz no asymmetry could be detected within 4 × 10-13 v. The stabilized frequency-being independent of the modulation width-is reproducible to better than ±2 × 10-11 v. From the small dependence of the frequency on the I2 vapor pressure of -5 kHz/Pa an uncertainty of less than ±4 × 10-11 v is assumed. Thus the selected 127I2 lines at v = 582 THz/λ = 515 nm should be promising candidates as optical frequency or wavelength standards.