Page 378 - Tunable Lasers Handbook

338 Norman P. Barnes

12.0 -
11.0 -

10.0 -
9.0 -
h
a,
c.
8.0 -
0
5 7.0 -
.-
E
v 6.0 -
5
ET,
5 5.0 -
-
a,
B 4.0 -
3.0 -
2.0 -
1.0 -

40 42 44 46 48
Angle (degrees)
FIGURE 1 9 Phase-matching curve for AgGaSe, for a 2.10-km pump.

increase of the output with the input is often observed. Total efficiency suffers
from many of the same ambiguities as slope efficiency. It could imply the output
power or energy at one or both of the signal and idler wavelengths divided by
the pump power or energy. Photon efficiency normalizes the pump power and
energy and the output power or energy by the energy of the pump and output
photon, respectively. Thus. a unity photon efficiency would imply that the power
or energy efficiency would be in the ratio of the pump wavelength to the output
wavelength. Pump depletion usually compares the pump pulse transmitted
through the optical parametric oscillator with and without oscillation occurring.
As such, it is closest to the efficiency calculated using both the signal and idler
as outputs.
Optical parametric oscillation was first demonstrated using a pulsed pump
laser, a frequency-doubled Nd:CaWO, laser [50]. The threshold was reported to
be sharp and well defined at 6.7 kW, but was only achieved on about one in five
shots. A peak output power of 15 W at a signal wavelength of 0.984 pm was
reported, yielding an efficiency of about 0.002.
Continuous wave optical parametric oscillation was reported by using a
Ba,NaNbjO,, crystal [51]. It was pumped by a frequency-doubled Nd:YAG
laser. A threshold of 45 mW was observed when the wavelengths available