Coatings for Laser Applications
Lasers on the basis of Yb doped crystals or fibres have gained increasing importance over the recent years. High power cw lasers were developed on the basis of Yb:YAG as well as with Yb doped fibres. Yb:YAG and Yb:KGW lasers can also be operated as high power ns, ps or fs lasers.
Figure 1: Reflectance spectra of a HR cavity mirror (a) and a HR turning mirror (b)
Lasers with extremely high output power
(e.g. > 10kW cw) are often based on Yb:YAG. LAYERTEC
has developed different coating designs for handling extraordinary high fluences. The designs are optimized either for cw-radiation or ns-pulses or ps-pulses.
Short Wavelength Pass Filters
Figure 2: Transmittance spectrum of a steep edge short wavelength pass filter with HR(0°, 1030nm) > 99.9% and HT(0°,808 – 980nm) > 99.5% (rear side AR coated)
- Short wavelength pass filter with very steep edge for use as pump mirror for solid state lasers on the basis of Yb-doped materials (e.g. Yb:YAG, Yb:KGW, Yb-doped fibers)
- Also useful for Nd-doped and Yb-Nd-co-doped materials
- Transmittance T > 99 % at 808 nm – 990 nm, reflectance R > 99.9 % at 1030 nm, i.e. transition from the high transmittance range to the high reflectance range within 4 % of the laser wavelength
- Superior laser damage thresholds (100 MW / cm2 cw at 1064 nm *)
- Thermally and climatically stable
|*|| Measured with a high power fiber laser at Institut für Angewandte Physik, Friedrich-Schiller-Universität Jena |
Long Wavelength Pass Filters
Steep edge of a long wavelength pass filter can also be combined with a defined partial reflectance in the wavelength range of the laser radiation.
Figure 3: Transmittance spectrum of a steep edge long wavelength pass filter with HR (0, 915 – 980 nm) > 99.8 % and HT (0°,1030 – 1200 nm) > 97 % for use as output mirror of a fibre laser (rear side AR coated) Figure 4: Reflectance spectrum of an output mirror for a fibre laser which blocks the diode radiation at 980nm and has a partial reflectivity R = 10% for 1030 – 1100nm
Thin Film Polarizers
Figure 5: Reflectance spectra for s- and p-polarized light of a thin film polarizer which is designed for high laser damage thresholds for ps pulses (AOI = 55°)
Thin film polarizers are key elements for regenerative amplifiers in ns- and ps-lasers.
Picosecond Lasers on the basis of Yb Doped Materials
Picosecond lasers, i.e. lasers with pulse lengths of some hundred fs to 10ps can be built on the basis of Yb:YAG-, Yb:KGW- and Yb:KYW. These lasers enable materials processing without unwanted thermal effects such as melting, which results in unprecedented accuracy of the processes. Moreover, picosecond lasers don´t require chirped pulse amplification which reduces the costs compared to fs-lasers and the laser crystals don´t show thermal lenses which enables high output power. Recently, it was demonstrated that lasers with an average power of 400W (770fs, 1MHz) are possible on the basis of Yb:YAG slab crystals.
Picosecond laser optics require specially designed optics to achieve high laser damage thresholds. For detailed information please see here.
For GTI mirrors which are often used for pulse compression from the ps range down to a few hundred fs please see here.