Interferometric investigation of a diode laser source

Diode lasers provide a coherent light source in the near IR. They have many desirable characteristics, such as small size, high efficiency, and a single-longitudinal mode output as large as 15 mW, and they can be modulated at high pulse rates. An AlGaAs diode laser operating at 840 nm with an output of 5 mW was evaluated with a Smartt point-diffraction interferometer. The wave front observed had astigmatism of about 2 wavelengths present over the output beam divergence angle. In a modified Twyman-Green interferometer, the coherence length measured was greater than 15 m with high visibility fringes. This source was found to be stable and highly linearly polarized. When used as an interferometric source, many possibilities for small scale interferometers and test equipment are now viable.