Gires-Tournois-Interferometer (GTI) Mirrors (600 – 1600 nm)

Gires-Tournois-Interferometer (GTI) Mirrors

Gires-Tournois-Interferometer (GTI) mirrors are used for pulse compression in short pulse lasers such as Yb:YAG- or Yb:KGW-lasers. LAYERTEC also offers GTI mirrors for the Ti:Sapphire wavelength range and for other ultrafast lasers in the NIR spectral range. Compared to prism compressors, GTI mirrors reduce the intra cavity losses resulting in higher output power of the laser.

Special Features

Very high reflectance
Center wavelength, bandwidth and GDD according to customer specifications
Please note that bandwidth and GDD are closely connected. A high value of negative GDD results in a very narrow bandwidth
Spectral tolerance ±1 %
In-house design calculation and measurement capabilities
(GDD 250 – 1700 nm, reflectance measurement by CRD 210 – 1800 nm)

Table 1:LIDT Info

LIDT	Wavelength	Pulse Duration	Repetition Rate	Pulses at each Site	Beam Diameter	Measurements at
≈ 0.1 J/cm²	800 nm	150 fs				Laser Zentrum Hannover
≈ 225 mJ/cm²	1030 nm	44 fs	1 KHz	100 000-on-1	1/e² ≈ 750 µm	DESY Hamburg 2021

GTI-Mirrors for Yb:YAG and Yb:KGW-Lasers

Fig.1:GDD spectra of GTI-mirrors for 1040 nm with different GDD Values

a)-500 fs², -1300 fs²

b)-2500 fs², -5000 fs², -10 000 fs²

Typical reflectance values depending on dispersion:
- -500 fs²: R ≥ 99.99 %
- -1300 fs²: R ≥ 99.98 %
- -2500 fs²: R ≥ 99.97 %
- -5000 fs²: R ≥ 99.95 %
- -10 000 fs²: R ≥ 99.95 %

Fig.2:GTI mirror with nearly constant TOD

Fig.3:GTI mirror with positive GDD

Fig.4:GDD spectrum of a rear side GTI mirror with
GDD (0° – 10°, 1030 nm) ≈ -700 fs²

The light enters on the front side of the mirror which is AR-coated. Then it passes the substrate and hits the rear side which is coated with the GTI mirror. Rear side GTI mirrors are insensitive against surface contamination which sometimes distort the GDD spectrum of common front side GTI mirrors.

Optical Losses of GTI-Mirrors

Fig.5:Calculated reflectance spectra of a GTI mirror without absorption losses (black) and with typical absorption losses (grey)

Fig.6:Measured reflectance spectrum of a GTI mirror (design as calculated in Fig. 5)

GTI mirrors of LAYERTEC show high reflectance values (e.g. R > 99.98 % at 1030 nm). The reflectance can be measured exactly by CRD. The high reflectance proves that the absorption losses in the GTI mirrors are very small. This also results in very small thermal lensing inside these GTI mirrors if they are used in high power lasers.

Coating Homogenity and Reproducibility of GTI-Mirrors

Fig. 8 and Fig. 9 show that all GTI mirrors which were produced in these batches meet the specifications given in Fig. 7. Comparing mirrors from two batches the variation within a batch and between batches are much smaller than what is allowed by the specifications. The excellent reproducability of complex coating designs is the basis for the use of GTI mirrors in industrial short pulse lasers.

Fig.7:Calculated GDD spectrum of a GTI mirror: GDD-R (6°, 1020 – 1060 nm) ≈ -1000 ±200 fs²

Fig.8:Measured GDD spectra of 6 GTI mirrors which were coated in the same batch according to the design of Fig. 7

Fig.9:Measured GDD spectra of 6 GTI mirrors which were coated in a second batch according to the design of Fig. 7

Gires-Tournois-Interferometer (GTI) Mirrors (600 – 1600 nm)