Chirped mirrors and matched pairs

One can think of a chirped mirror as a Bragg mirror where the thickness of the layers slowly increases or decreases from bottom to top, so that the different “colours” are reflected at different depths resulting in different group delays which gives a non-zero GDD.

There are unavoidable residual GDD oscillations of such mirrors. If necessary, they can be suppressed for example by using chirped mirror pairs where the oscillations of two different mirrors cancel each other out.

It is possible to produce chirped mirrors spanning more than one optical octave and having extra features like a high transmission pumping pass band.

The complexity of the design is determined by the spectral width and desired GDD level. A more complex design is usually characterized by an increased electric field inside the layer stack, which is directly correlated to the laser induced damage threshold.

There are several design strategies which carefully optimize the electric field enhancement to improve the LIDT.

On the other hand, nonlinear effects (e.g. nonli­ne­ar absorption) can lower the LIDT if pulses get very short (< 40 fs). There are some tricks in design strategy and during the manufacturing process we can use to reduce these effects.

With increasing laser power, the fluence can be lowered by enlarging the spot size on the optics. Most complex pairs of chirped mirrors, single chirped and GTI mirrors can be deposited on substrates up to diameter 4'' with the standard IBS machines. Larger sizes are possible on request.

LASEROPTIK’s cooperation with leading research institutes in the field of ultrashort lasers and frequency combs helps to generate new results about the producibility of complex GDD coatings of which some findings are published.*

* Chia, S.-H., Cirmi, G., Fang, S., Rossi, G. M., Mücke, O. D., Kärtner, F. X., Two-octave-spanning dispersion-controlled precision optics for sub-optical-cycle waveform synthesizers, in: Optica, Vol. 1 (2014), Iss. 5, pp. 315-322