Ultrafast monochromator  From Wikipedia, the free encyclopedia
Jump to: navigation, search  An ultrafast monochromator is a
monochromator that preserves the duration of an ultrashort pulse
(in the femtosecond, or lower, time-scale). Monochromators are
devices that select for a particular wavelength, typically using
a diffraction grating to disperse the light and a slit to select
the desired wavelength; however, a diffraction grating
introduces path delays that measurably lengthen the duration of
an ultrashort pulse. An ultrafast monochromator uses a second
diffraction grating to compensate time delays introduced to the
pulse by the first grating and other dispersive optical
elements.  Diffraction gratings are constructed such that the
angle of the incident ray, θi, is related to the angle of the
mth outgoing ray, θm, by the expression   m \lambda = d (
\sin{\theta_i} - \sin{\theta_m}).  Two rays diffracted by
adjacent grooves will differ in path length by a distance . The
total difference between the longest