Development of a Wavelength Stabilized Light Source with a Laser Diode

Usually frequency stabilized lasers have been used as light sources for high precise distance measurements. However, accuracy of those measurements is worse in air than in vacuum because wavelengths of such lasers fluctuate according to fluctuation of the refractive index of the air. Therefore a wavelength stabilized light source whose wavelength is not influenced by the refractive index of the air is desirable for distance measurements. This paper describes a wavelength stabilized light source with a laser diode using a air-gap etalon as a standard of wavelength. As the optical length between two mirrors of the etalon changes according to the refractive index of the air, the wavelength in air can be stabilized. Our new wavelength control system does not require any electrical standard. At the same time the system realizes spectral linewidth reduction by widening the frequency range of it. Experimental results are as follows: the wavelength stability in air estimated with square root of the Allan variance is 3.0×10-9 (at 10 sec of integration time) and the spectral linewidth, that for free running is 10 MHz, is reduced to 650 KHz with electrical feedback.