The ultrafast monochromator aims to preserve the temporal duration of a femtosecond source, by combining more than one grating.
A major application is the extraction without time-broadening of a single laser harmonic of high order from a generated by a few femtosecond laser interacting with a gas target.
The conditions to be fulfilled by the ultrafast monochromator are
- that the different optical path introduced during the dispersion with one grating is removed during the diffraction operated by a second grating;
- that the path length of the rays propagating inside the monochromator are all the same.
This latter condition imposes also the correction of the optical aberrations introduced by the monochromator optical components.
When these conditions are both actuated, the design is compensated for the time broadening and the ultrafast properties of the source are preserved by the monochromator.