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

The quality factor
Q
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
G
and decreasing bandwidth
\delta v
with increasing single-pass gain G
0
. An approximate theoretical treatment shows that the bandwidth root gain product should be a constant
\delta v \sqrt{G}
= 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 2.10
⁴
c/s was realized. The amplifier device was used for a measurement of electron densities down to 3.10
¹²
cm
^-3
in a helium plasma.