Page 190 - Tunable Lasers Handbook

168 F. J. Duarte

Cyanines
- Merocyanines
Xanthenes

Coumarins
Stilbenes
- Oligophenylenes
- Oxadiazoles
I I I I I I I 4 I
300 400 500 600 700 800 900 1000 1100
Emission Wavelength (nm)
FIGURE 1 .4pproximate wavelength coverage achieved with different classes of laser dye molecules.

techniques that have now found wide applicability in lasers in general. Impor-
tant contributions to the laser field first demonstrated in dye lasers include fre-
quency stabilization techniques. pulse compression techniques, dispersive oscil-
lator configurations, and numerous cavity and resonator innovations.
Although dye molecules have been demonstrated to lase in the three states
of matter, it is in the liquid phase that dye lasers have made their most signifi-
cant impact. Recently. however, there has been a resurgence of work in solid-
state dye lasers. Hence a section of this chapter is especially devoted to this
topic.
This chapter is intended to provide an expeditious guide to the performance
and basic features of dye lasers. For an in-depth approach to the subject, the
reader should consult the references provided in the various sections and the fol-
lowing books: High PoM.er Dye Lasers [l], D?e Laser Pririciples [7], Dye Lasers
[XI, and Selected Papers on Dye Lasers [9]. These works should also be con-
sulted for a historical perspective on the subject.

1 .1 The Molecular Gain Media
Laser dye molecules are large, with atomic weights in the 175- to 1000-amu
range (see the Appendix at the end of this chapter). These molecules exhibit a
wide absorption spectrum with broad and strong absorption maxima correspond-
ing to S,+S,t electronic transitions (Fig. 2). Here, dye molecules are considered
simply from an energetic perspective with an excitation dynamics involving sev-
eral energy levels. A feature of dye laser molecules is that each electronic state
contains a multitude of overlapping vibrational-rotational levels. This plethora of
closely lying vibrational levels gives origin to the broadband gain and tunability
features that are so characteristic of dye lasers.