Polarization Suppression of Parasitic Modes

摘要

In a multi-pass laser optical system orthogonal polarization of any two immediately adjacent optical passes allows suppression of internal parasitics caused by overlap of laser radiation on successive passes through a laser oscillator or amplifier, allowing increased operating efficiency and closer spacing of adjacent optical paths. Multiple-pass laser configurations are frequently used in lasers to fill an active laser medium with a single oscillating mode even though the laser region may have a large Fresnel number. However, when the adjacent passes of optical radiation through the laser medium lie too close to one another, the overlap of energy from one beam to another can regenerate to form a parasitic oscillation within the device. This parasitic is undesirable because it increases mirror flux loading and robs the output beam of laser energy. Thus if the consecutive mirrors of a multi-pass laser system are positioned to almost face each other, a parasitic oscillation can be set up between them. A conventional technique for suppressing these is to space the mirrors apart. This has the disadvantage of extending the size of the laser, which causes unnecessary weight in the device. Moreover, in a chemical laser or similar device with a short storage time within the laser medium, laser excitation is wasted because of the regions between the optical path where no radiation is present to extract the laser energy.