Experimental research for measuring spectral width of visible semiconductor lasers has been done, aiming to stabilize frequency of semiconductor laser at an absorption line of a molecule.
1. Behavior of oscillation mode of 670nm semiconductor laser, which depends on optical feed back, was investigated. A Frabry-Perot etalon with a simple structure was made for filtering single frequency peak of multimode output of the laser. It shows good attenuation of side lobes.
2. A scanning Michelson interferometer was made to measure visibility active as a function of optical path difference. The obtained curve makes possible to calculate optical patil length of the semiconductor laser and also oscillation mode can be analyzed.
3. Optical phase modulation of 633nm beam of a He-Ne laser at modulation frequency of 50 and 100MHz was examined and a clear peak of sideband was observed by optical beat detection. The results shows that the sideband will be useful for detecting molecular absorption lines since its central frequency can be swept by changing modulation frequency. This system can be used for the semiconductor laser.
4. Detection of optical beat note, which should be generated by mixing 670nm beams of two semiconductor lasers, was done intending to measure the spectral width. In spite of precise alignment of optical axises and wave surface of both beams and fine tuning of the oscillation frequency of the lasers, the beat has not detected. This is the most important and necessary measurement for stabilizing the laser at a narrow molecular absorption line. We will continue this experimental research improving our measuring system and blushing tip our experimental technique.