7C2 - Theoretical and experimental investigation of regenerative laser amplifiers and their applications

The quality factor of optical resonators increases if the cavity losses are reduced by means of an active medium. In this case, the resonator works analogous to a classical RF amplifier, the amplification of which is increased by feedback. Significant for this amplifier type is increasing gain and decreasing bandwidth with increasing single-pass gain G0. An approximate theoretical treatment shows that the bandwidth root gain product should be a constant = const. Our experiments show that this relation is well performed at low signal intensities. At the point nearest to threshold a maximum gain of 20 000 and a minimum bandwidth of 2.10⁴c/s was realized. The amplifier device was used for a measurement of electron densities down to 3.10¹²cm^-3in a helium plasma.