In situ small-signal gain of solid-state lasers determined from relaxation oscillation frequency measurements

We present a simple, in situ technique to calculate the small-signal gain of typical solid-state continuous-wave lasers, such as Nd:YAG and Nd:YLF lasers, by measuring the frequency of the relaxation oscillation noise peak. The laser's small-signal gain can be directly calculated from the frequency of the relaxation oscillation with knowledge of the upper-state lifetime, the cavity round-trip time, and total losses, which are typically well-known values. When the laser is pumped many times above threshold the losses do not need to be known accurately. This technique is compared with the traditional method of changing output couplers to establish its accuracy.