Frequency Comparison of I -Stabilized Nd : YAG Lasers

A first international comparison of I2-stabilized Nd : YAG lasers has been made between the National Research Laboratory of Metrology (NRLM), Tsukuba, Japan, the Joint Institute for Laboratory Astrophysics JILA (formerly the Joint Institute for Laboratory Astrophysics), Boulder, CO, the National Institute of Standards and Technology (NIST), Boulder, and the University of Colorado, Boulder. The results of the comparison show that the square root Allan variance of the portable NRLM laser has reached 2 10 14 when the integration time is larger than 300 s. Matrix measurements were made for five hyperfine components from a6 to a10 of the R(56)32-0 line. The averaged frequency difference between the NRLM and JILA lasers for four measurements made on three separate days was 4996 Hz (NRLM-JILA, at 532 nm) with a standard deviation of 88 Hz.