Sub 10-fs Pulses with Chirped Laser Mirrors

The development of broadband saturable semiconductor absorber mirrors and of dispersion-engineered chirped multilayer dielectric mirrors has allowed the realization of self-starting ultrashort laser pulses, which routinely reach sub-10 fs pulsewidths and peak powers above the megawatt level. 

Chirped mirror only Bragg wavelength chirped 

Double-chirped mirror Bragg wavelength and coupling chirped 

Instead of varying the thicknesses of the layers, one can also produce chirped mirrors by smoothly altering the indices of refraction and the difference between them (nr - i) (Fig. 6.33). 

These mirrors may be regarded as one-dimensional holograms that are generated when a chirped and an unchirped laser pulse from opposite directions are superimposed in a medium where they generate a refractive index pattern proportional to their total intensity [693]. When a chirped pulse is reflected by such a hologram, it becomes compressed, similar to the situation with phase-conjugated mirrors. 

Bottom reflector (AlAs/AIGaAs Bragg mirror) 

A combination of saturable semiconductor media in front of a chirped mirror and KLM techniques can be used for reliable operation of sub-10-fs pulses. In Fig. 11.30 such a multilayer saturable absorber is illustrated. 

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