WAVELENGTH STABILIZATION OF A DIODE-LASER BY COMPARISON WITH AN INCREMENTAL MEASURE

This paper describes a measuring arrangement which allows to compare the wavelength in air of a diode laser with the length of an incremental measure and to control it so that it is kept constant even during short-term atmospheric disturbances. The opto-mechanical arrangement consists of a commercial measuring probe as length standard (approx. 60 mm) [1] and a counting diode laser interferometer [2]. The probe movement is simultaneously measured by both measuring systems. By means of digital control and using the diode current as control quantity, the wavelength in air of the diode laser is so controlled that the displacement lengths measured by both measuring systems are the same. The test results show that the wavelength in air can be kept constant with a relative uncertainty of U-lambda/lambda almost-equal-to 4.10(-7) even if the refractive index of the air varies considerably (approx. 10(-5)).