Stabilization and frequency measurement of the I/sub 2/-stabilized Nd:YAG laser

Abstract
We report improved stabilization results for and progress toward a more accurate frequency measurement of the 532 nm iodine-stabilized system based on a frequency-doubled Nd : YAG ring laser. We confirm the CCL-adopted frequency well within its stated uncertainty ( 40 kHz). HERE are a number of attractive metrological features of the green 532 nm light obtained by frequency-doubling the output of the commercially available stable Nd : YAG ring lasers. These advantages include high visibility, exceptionally low intrinsic frequency and amplitude noise levels, and the flexibility to realize various power levels as needed from submilliwatts to literally tens of watts. Because of the strong absorption and narrow linewidth of the I lines at 532 nm, it was realized early on that they form an almost ideal stabilization medium to complement the diode-pumped stable Nd : YAG laser. By now, groups at Stanford University (1) and JILA (2)-(4) have investigated a number of these features, including hyperfine structures, frequency intervals between several absorption lines (5), the absolute optical frequency, as well as some details of building an optical frequency standard based on this system. The 1997 meeting of Consultative Committee for Length (CCL) led to a recommended value for the optical frequency of one particular component, , of the R(56) 32-0 transition. A number of metrology groups have built stabilized laser systems based on these hyperfine resonances, and recently we have participated (6) in the first international intercomparison with the portable system "Y1" of the National Research Laboratory for Metrology (NRLM).