Passive

switching of IR lasers (N
2O as well as CO
2) has been applied for the detection of coincidences within a few 100 MHz between laser lines (ν
L) and molecular transitions (ν
M). Polar (
12CH
3F,
13CH
3F, C
2H
5OH, and C
6H
5CH
3) as well as nonpolar molecules (SiH
4, GeH
4, CCl
4, C
2H
4, C
3H
4, and C
6H
6) have been studied. The phenomenon depends strongly on the frequency mismatch

combinations between laser lines and molecular absorption lines were found to produce the

-switch effect.