Chirped Mirror Pairs

Chirped mirrors are used to compensate dispersion-related travel time differences of ultrashort laser pulses. A chirped mirror pair (consisting of two chirped mirrors) is required if the oscillations in the GDD curve are strong. This is especially the case for mirrors with high bandwidths.

Chirped mirror pair

The GDD curve of a chirped mirror does not represent a straight-line curve, but shows oscillations. How strong these are depends, among other things, on the spectral bandwidth. For GDD bandwidths smaller than the bandwidth of a comparable Bragg mirror, the oscillations are rather small. Mirrors with high bandwidth, on the other hand, show strong GDD oscillations.

Chirped mirror pair figure
  GDD spectrum of a negative dispersion mirror pair

A correction can be achieved by using corresponding mirror pairs. They consist of two differently coated dielectric mirrors with opposite GDD curves, between which the laser beam can be reflected back and forth as often as desired (see figure). These mirrors are optimized for a small angle of incidence so that a large number of reflections can be achieved.