Page 376 - Tunable Lasers Handbook

336 Norman P. Barnes

12.0
11.0 1, 1.064pm Pump
t \

35 39 43 47 51
Angle (degrees)
FIGURE 1 7 Phase-matching curve for AgGaS, for a 1.061-pn pump.

Of perhaps more significance is the introduction of better nonlinear crystals.
particularly ones with a larger nonlinear coefficient. Of particular note in the
way of visible crystals are KTP, BBO, and LBO. Crystals with nonlinear coeffi-
cients as large as those available with these more recent crystals were not gener-
ally available in the early developmental stages of optical parametric oscillators.
In the infrared, AgGaSe, has developed to the point where it is presently com-
mercially available for applications in the mid-infrared region. Although this
crystal has been known for some time, the availability and the absorption in the
near-infrared region limited its utility. In addition. substantial progress has also
been made with the commercialization of ZnGeP,.
Pump lasers have also improved both in power and beam quality, a definite
advantage when nonlinear optics are being used. Improvements such as unstable
resonators and graded reflectivity output mirrors have made pump lasers with good
beam quality as well as high energy per pulse available. The beam quality of pump
lasers is often limited by thermal effects. However, as laser diode array pumping of
solid-state lasers becomes more common, the beam quality should improve even
more since the thermal load on a laser diode array-pumped solid-state laser is less
than a similar lamp-pumped solid-state laser at the same average output power. In
addition, injection seeding techniques have narrowed the linewidth of the pump