LM-0300 Fabry Perot Spectrum Analyzer

This experiment shows the properties of optical resonators especially the „Fabry Perot“ (FP) resonator which is the most important of all stable laser resonators. The properties and behavior of such a resonator will be discussed and measured as well as the resonance condition, the free spectral range and finesse. The stability criteria of confocal, hemispherical and plane parallel resonator types are calculated and measured. Finally, the resonator will be used as a spectrum analyser, a so called scanning Fabry Perot. The mode spectra of the provided green single mode diode pumped solid state laser (DPSSL) and optional two mode HeNe laser is measured. The resonator mirrors are mounted in precision adjustment holders. One mirror is mounted on a low voltage piezoelectric transducer (PZT) which is controlled in amplitude and frequency by means of a voltage (0-150 V) controller. The other one is mounted into a precise translation element to achieve the perfect confocal match for curved mirror. The PZT periodically changes the length (0 to 10 µm) of the cavity sweeping over some resonances. The signal of the photodiode and the triangular PZT scanning amplitude are displayed on an oscilloscope showing the Airy function for some resonances. By using the known distance of the FP mirror, the free spectral range is determined and is used to calibrate the horizontal axis of the oscilloscope. The mode spectra of the DPSSL - Laser is measured and interpreted by this method. Surprisingly, the green emitting DPSSL emits a very pure single mode if the temperature and injection current are properly controlled. In addition, an optional two mode HeNe probe laser can be used to measure the mode spacing with the SFP. Some parts of this experiment can also be used in connection with the experimental HeNe-Laser, to demonstrate the single mode operation, when an etalon is used inside of its cavity. By tuning it, even the gain profile of the HeNe laser can be measured (see extension LE-0350).