Examples of Investigations and Measurments

By using the integrated gear and pinion drive of the mirror adjustment holder provided with the Piezo element, the length of the resonator can be altered in a precise way.
Once the confocal case has been obtained, the amplitude of the interferogram increases significantly. The set-up is now well aligned to measure the most essential parameters of the Fabry Perot resonator.

The probe laser emits two orthogonally polarised modes. If the amplitude of the Piezo voltage is adjusted in such a way that at least two orders of the resonator are covered, one gets a graphical representation on the oscilloscope as shown on the left side. The spacing of the orders allows for the determination of the free spectral range provided that the distance of the laser mirrors is known.
The free spectral range can be measured now for different distances of the mirror.

By suitable choice of the amplitude of the Piezo voltage and of the time base of the oscilloscope, one gets the graphical representation as shown on the left. From this the finess of the Fabry Perot resonator can be calculated. Special attention has to be paid to the fact that the value of the finesse may deviate significantly from the theoretical value due to the mirror€˜s reflectivity. In this context the real finesse is introduced.

From (B) the free spectral range of the Fabry Perot resonator is known. Therefore the spectral mode distance of the used HeNe probe laser can now be determined. It becomes apparent that the Fabry Perot resonator is a suitable instrument for monitoring for monitoring the modes of other laser. The representation of the modes of a laser is an important result of this experiment.