Ultrafast monochromator

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 mλ. The total difference between the longest and shortest path within a beam is computed by multiplying mλ by the total number of grooves illuminated. For instance, a beam of width 10 mm illuminating a grating with 1200 grooves/mm uses 12,000 grooves. At a wavelength of 10 nm, the first order diffracted beam, m = 1, will have a path length variation across the beam of 120 μm. This corresponds to a time difference in the arrival of 400 femtoseconds. This is often negligible for picosecond pulses but not for those of femtosecond duration. ==Applications==

A major application is the extraction, without time-broadening, of a single high-order harmonic pulse out of the many generated by an ultrafast laser pulse interacting with a gas target. ==See also==