Abstract
Recent years, laser diodes (LDs) are popular in optical applications and the precision engineering, because the LDs have long lifetime, high power, and compact size. The drawback of LDs is typically low frequency stability in comparing with the gas lasers (HeNe lasers), which causes the decreasing of measurement accuracy in displacement measuring interferometers. To improve the frequency stability, the LDs can be locked to some atomic-molecular transitions. The Iodine molecular (I2) can be used as a frequency reference for LDs at the wavelength near 633nm. In this paper, we propose a phase modulation with an electro-optic modulator (EOM) at high modulation frequency to achieve the frequency stabilized LDs. The center frequency of LDs is locked to a 127I2 hyperfine component of transition P(33), which is near 633nm. In this experiment, the long-term frequency stability of 10-10 can be achieved. The stabilized LDs is used as the light source for a modified Mach-Zehnder interferometer. The Mach-Zehnder interferometer can be combined with a direct phase determination method to obtain pm resolution of displacement measurements.
