Chirped mirrors and matched pairs

Dispersive Coatings

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.

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

HT 532 nm HR 650-1100 nm /0-15° GDD opt.
[B-10888]HT 532 nm HR 650-1100 nm /0-15° GDD opt.

532 nm: T > 95%; 650-1100 nm: R > 99.9%; 780-1010 nm: GDD (R) = -88 → 0 fs² ± 50 fs² (IBS-coating)

HR 730-930 nm /7° p GDD -125 fs²
[B-12658]HR 730-930 nm /7° p GDD -125 fs²

730-930 nm: Ravg > 99.9%, GDD ± 40 fs² vs. theoretical curve (IBS-coating)


Two examples for chirped mirror pairs

HT 532 nm HR 675-975 nm /7° p GDD opt.
[B-09709-P01+02]HT 532 nm HR 675-975 nm /7° p GDD opt.

target specifications for a mirror pair, best effort (IBS-coating):
532 nm: T > 98%; 675-975 nm: Rp > 99.9%, GD (R)-ripple < 2 fs

HR 700-900 nm /7° s GDD opt.
[B-09813-P01+02]HR 700-900 nm /7° s GDD opt.

700-900 nm: Ravg > 99.9%; 710-860 nm: GDD ± 10 fs² (IBS-coating)


Example for chirped mirror pairs with combination of positive and negative GDD

A combination of positively and negatively chirped mirrors gives low average dispersion while having significantly lower absorption losses than metal mirrors.

HR 830-1230 nm /45° s GDD opt.
[B-12544-P01+02]HR 830-1230 nm /45° s GDD opt.

830-1230 nm: R > 99.8%, GD = const ± 3 fs, GDD = 0 ± 30 fs² (IBS-coating)



House cricket

Chirping by nature: House cricket
(lat. Acheta domesticus)