Page 83 - Tunable Lasers Handbook

64 Charles Freed

those subjects. Insofar as CO, laser applications are concerned, Pate1 grouped
them into ten categories listed [5] as follows:
1. Science
High-resolution spectroscopy
Saturation spectroscopy
Two-photon spectroscopy
Nonlinear optics
Raman scattering and Raman lasers
2. Pollution detection
3. Industrial applications (materials fabrication)
Vaporizing: cutting, drilling, material removal, etching, scribing, trimming, etc.
Melting: welding, cladding, alloying, etc.
Submelting: annealing, hardening, and other phase changes
4. Communications
5. Pumps for tunable lasers and for X-ray, IR, and far-IR lasers
6. Laser-induced fusion
7. Isotope separation
8. Medicine and surgery
9. Metrology, remote sensing, and radar
10. Military
The CO, lasers that were developed for these applications range in size from a
few cubic centimeters that can easily be held in one hand, to many cubic meters
that weigh several tons and occupy an entire building. The lasing time durations
may range from less than 10-12 sec to cw, with peak and average power levels
greatly exceeding a terawatt and megawatt, respectively. The laser excitation
schemes used in the past include conventional dc or rf discharges, high-energy
electron beams, X rays, gas dynamic, and nuclear pumping. The pressures at
which CO, laser gas mixtures were operated range from less than 1 Torr to
nearly 100 atm.
Within the scope of a single book chapter the amount of material that can be
discussed must be severely limited. Accordingly, only those aspects of CO, laser
physics and engineering will be covered here that are most appropriate for a
book on tunable lasers.
We should mention at this time that very little emphasis will be given to
continuously tunable CO, lasers, because such lasers are generally very com-
plex, expensive, and difficult to build and maintain. Continuously tunable CO,
lasers operate at very high pressures (8 to 15 atm typical), and must have very
complex optical cavities in order to provide continuous tunability. Almost invari-
ably they have short output pulses (<lO-7 sec) leading to poor spectral purity.
Although high-pressure continuously tunable CO, lasers have been built in the
past [6-151 and are certainly feasible to construct, to the best of my knowledge
such lasers are not commercially available at the present time.