Analysis of a Nondegenerate Two-Photon Giant-Pulse Laser

In a recent article
¹
to which we shall refer as [S&B], a two-photon laser was proposed and analyzed. This device consists of a cavity resonant at frequency v
A
and containing ions of type B with an inverted population N
B
/V between levels separated by an energy difference hv
B
such that v
B
= 2v
A
; it is necessary that the system not lase at v
B
, which criterion can be satisfied by low reflectivity of the cavity at frequency v
B
, by strong parasitic absorption in the laser material near frequency v
B
, or preferably by a choice of ion such that the transition v
B
is highly forbidden to a single-quantum process. The authors of [S&B] thus show that a certain priming density of photons of frequency v
A
will provoke the simultaneous emission from the inverted population N
B
of pairs of photons v
A
at a rate exceeding the cavity loss,t he process diverging until the population inversion is eliminated.