374 Ultrashort Sources II: Examples
Two methods of short pulse generation that use either ultrashort cavities
(Fabry–Perot dye cells of thickness in the micron range) or no traditional cavity
at all (distributed feedback lasers) have successfully been developed for (but are
not limited to) dye lasers.
In distributed feedback lasers two pump beams create a spatially modulated
excitation that acts as a Bragg grating. This grating serves as the feedback
(resonator) of the laser and is destroyed during the pulse evolution. This short
cavity lifetime together with the small spatial extend of the gain volume can
produce subps pulses whose frequency can be tuned by varying the grating
period [129,130]. The latter is determined by the overlap angle of the