Page 174 - Tunable Lasers Handbook

4 CO, Isotope lasers and Their Applications 153

one with which the 4.3-pm standing-wave saturation resonance and the subsequent
line-center stabilization of a CO, laser were first demonstrated through the use of
the 4.3-pm fluorescence signal in 1970, as was discussed in Sec. 8 of this chapter.
For more than 25 years the dual requirements of modularity of laser design
and interchangeability of parts have provided a vast amount of convenience and
savings both in time and cost. But such requirements have perforce introduced
certain limitations in design and performance. Moreover, the laser designs and
components were developed more than 25 years ago. Extensive experience
gained by working with these lasers clearly indicates that updated designs could
easily improve the short-term and long-term stabilities by at least one to two
orders of magnitude. However, the instrumentation currently available is not suf-
ficient to measure definitively even the stabilities of our present lasers.
In the research, technology, and calibration of CO, laser transitions the main
emphasis was on the regular bands of the rare CO, isotopes at MIT Lincoln Labo-
ratory. The primary calibration of the regular bands of the most abundant 12C1602
species was first carried out at the NBS (now NIST) in Boulder, Colorado. Cali-
bration of hot bands with line-center-stabilized lasers was started at NRC in
Canada in 1977 [lo01 and continued at NBS/NIST [loll, much of it only very
recently in 1994 [80,8 1,831. Precise calibration of the sequence bands transitions

FIGURE 23 The optical portion of the two-channel CO, calibration system. (Reprinted with
permission from Freed [75]. 0 1982 IEEE.)