Misalignment Sensitivity of the Output Power

Abstract

The misalignment of the resonator mirrors results in a change of the output power of a laser resonator due to two mechanisms (we intentionally use the term change instead of decrease since in unstable resonators the power can also increase with mirror tilt); the diffraction losses are increased leading to a higher laser threshold and the cross sectional area of the laser beam in the medium is decreased resulting in a lower mode volume (Fig. 14.1). The resonator scheme determines which of these two effects dominates. In stable resonators with multimode operation, the decrease of the power is caused by the decreasing mode volume since additional diffraction losses are only generated if low order transverse modes get clipped by an aperture. In fundamental mode operation, on the other hand, the change in mode volume does not play any role and the output power drops due to the increased losses. We discussed the sensitivity of the losses to misalignment in Sec. 5.4 and Sec. 7.4. The reader who is not familiar with the properties of passive misaligned resonators should first go through Sec. 5.4.