Determination of the fundamental laser parameters using an acoustooptical device

It is shown that an acoustooptical modulator used inside the laser cavity can emulate a variable-transmission mirror. The transmission of the equivalent mirror formed by the modulator and the output coupler is a function of a known applied voltage, in such way that in a single run it is possible to determine the usual behavior of the output power as a function of the mirror transmission. By analyzing this dependence it is possible to obtain laser parameters such as unsaturated gain, pumping rate, and internal losses. It is also demonstrated that an analytical expression for the internal losses can be obtained. This technique is used to characterize a CW Nd:YAG laser, and it is shown that the rod quality, as well as the depolarization due to the thermal birefringence, are responsible for losses as high as 10% per pass. This is a simple and reliable method for characterizing a laser system in the CW regime.<
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