Three characteristics figure high on the wish lists of many dye laser users: extremely narrow linewidth, high average power, and ultrashort pulses. An individual dye laser can offer one of these features, but not all three. The inability to combine narrow linewidth and short pulses is fundamental because the minimum attainable linewidth and shortest possible pulse duration are related according to the formula:

(Svelto, 1989). This expresses a Fourier transform relationship between time and frequency domains; it is a fundamental physical limit.

The problem of combining high average power with either of the other goals is more practical. In practice, the highest average powers come when the dye is pumped with high average powers from a pulsed laser (generating pulses lasting tens of nanoseconds), or from a flashlamp (generating dye pulses lasting microseconds). Neither mode of operation produces either ultranarrow bandwidth or ultrashort pulses. Continuous-wave operation is needed to produce extremely narrow bandwidth, but it yields limited output power. Although ultrashort pulses in the picosecond or femtosecond regimes have high peak powers, they are so short that they contain little energy, thus limiting average power.

Several trade-offs are inherent in the choice of pump sources, some of which are summarized in Table 17.1. Copper vapor, excimer, neodymium, and nitrogen lasers all provide pump pulses lasting a few to tens of nanoseconds, but their repetition rates differ, Flashlamp pulses are considerably longer. Rare gas ion and neodymium lasers can provide continuous-wave pumping, although neodymium pump powers are...