Portable I-2-stabilized Nd : YAG laser for international comparisons

We have established a compact and transportable I-2-stabilized Nd:YAG laser for international comparisons of laser frequency. The root Allan variance of the portable laser has reached 3.9 x 10(-14) when the integration time i s longer than 200 s, The results of an international comparison between the National Research Laboratory of Metrology (NRLM), Tsukuba, Japan and the J ILA (formerly the Joint Institute for Laboratory Astrophysics), Boulder, CO , USA show that the frequency difference of the portable laser NRLM-Y1 and the JILA laser JILA-W (f(NRLM-Y1) - f(JILA-W)) was -2.5 kHz, when the cold- finger temperatures of NRLM-Y1 and JILA-W were kept at -10 degreesC and -15 degreesC, respectively. The averaged frequency offset between two NRLM las ers (f(NRLM-Y1) - f(NRLM-Y2)) was -1.1 kHz, A frequency variation of about 1.2 kHz was found for the frequency offset between two NRLM lasers, after N RLM-Y1 was taken for a round trip to Sydney for a comparison organized by t he National Measurement Laboratory, (NML), Australia.