OUTPUT  CHARACTERISTICS

     The output characteristics of a dye laser are highly dependent on the optics employed. A laser employing broadband optics would feature a naturally broad spectral width, typically spanning almost the entire range of the dye (especially in a laser-pumped dye laser, in which gain is usually large); this can be as large as 100 nm. A laser with such characteristics is not particularly useful, so wavelength selection is invariably employed.

       Use of a diffraction grating alone as a wavelength selector (with suitable beam expanding optics allowing utilization of a large area of the grating surface) renders a spectral width of 0.01 nm, which is suitable for many applications, but to reduce linewidth an intracavity etalon is often included in the optical path. Use of an etalon along with a diffraction grating can render spectral widths as low as 0.0005 nm. Such line widths are required when a dye laser is used as a tunable laser source for spectroscopy. Etalons may be angle- or pressure-tuned, with pressure tuning preferred for simplicity. As a modelocked laser, dye lasers have produced the shortest pulses produced from any laser source. The wide gain bandwidth of a typical dye allows the production of a series of extremely short pulses, in the femtosecond range.