KrF, XeCl, XeF Lasers (248 nm, 308 nm, 351 nm)

Cavity Mirrors

Fig.1:Reflectance spectrum of a cavity mirror for 308 nm

Oxide coatings on fused silica for high mechanical stability
R (0°, 248 nm) > 99.0 %, R (0°, 308 nm) > 99.9 %, and R (0°, 351 nm) > 99.9 %
Coatings can be produced by IAD, magnetron sputtering, or IBS
These cavity mirrors require a fluorine- or chlorine-resistant laser tube window.

Fluorine-Resistant Cavity Mirrors

Fig.2:Reflectance spectrum of a fluoride KrF cavity mirror

Fluoride coatings and CaF₂ substrates for high stability against fluorine
These cavity mirrors are produced by thermal or electron-beam evaporation on CaF₂ or MgF₂ substrates.
Laser mirrors with R > 98 % at 248 nm, 308 nm, and 351 nm

Output Couplers

Fig.3:Reflectance spectrum of an oxide output coupler with R (0°, 308 nm) = 50 % ±3 %

Oxide coatings on fused silica
These output couplers require a fluorine- or chlorine-resistant laser tube window.
PR coatings with the following tolerances:
- ±2 % for R = 10 % … 30 %
- ±3 % for R = 30 % … 75 %
- ±2 % for R = 75 % … 90 %
- ±1 % for R > 90 %

Fluorine-Resistant Output Couplers

Fig.4:Reflectance spectrum of a fluoride output coupler with
R (0°, 248 nm) = 25 % ±3 %

Fluoride coatings on CaF₂ or MgF₂
Coating process: thermal or electron-beam evaporation
PR coatings with tolerances of:
- ±2 % for R = 10 % … 20 %
- ±3 % for R = 20 % … 75 %
- ±2 % for R = 75 % … > 90 %

Windows and Lenses

Fig.5:Reflectance spectra of an AR coating for 308 nm
and AOI = 0° – 30°

High-quality mirror substrates, windows and lenses made of fused silica

Turning Mirrors

Fig.6:Reflectance spectra of a turning mirror for 308 nm, produced by IBS (reflectance measured in s- and p-polarization by CRDS)

Table 1:Reflectance of turning mirrors (oxide coatings on fused silica, not fluorine-resistant)

Coating	R (AOI = 0°)	Rs (AOI = 45°)	Rp (AOI = 45°)
248 nm IAD	> 99.0 %	> 99.5 %	> 99.0 %
248 nm sputtering	> 99.7 %	> 99.8 %	> 99.6 %
308 nm IAD	> 99.7 %	> 99.8 %	> 99.5 %
308 nm sputtering	> 99.9 %	> 99.9 %	> 99.7 %
351 nm IAD	> 99.9 %	> 99.9 %	> 99.7 %
351 nm sputtering	> 99.95 %	> 99.95 %	> 99.9 %

Attenuators

Fig.7:Transmittance spectrum of a sputtered (IBS) attenuator for 308 nm with precisely adjusted and thermally stable transmittance of T = 0.08 % at AOI = 45° (unpolarized light)

LIDT and Lifetime Data

Table 2:LIDT of Oxide Coatings

Coating	LIDT* [J/cm²]
HR (0°, 248 nm) IAD	10 J/cm² (1-on-1) 5 J/cm² (1000-on-1)
HR (45°, 248 nm) IAD	10 J/cm² (1-on-1)
* Measurements were performed at Laser-Laboratorium Göttingen and at Friedrich-Schiller-University Jena

Table 3:Lifetime of fluoride coatings

Coating	Lifetime
HR (0°, 248 nm)	2 × 10⁸ pulses*
PR (0°, 248 nm) = 50 %	2 × 10⁸ pulses*
AR (0°, 248 nm)	2 × 10⁸ pulses**
HR (0°, 308 nm)	2 × 10⁸ pulses**
HR (0°, 351 nm)	2 × 10⁸ pulses**
PR (0°, 351 nm) = 25 %	2 × 10⁸ pulses**
* Fluence: 100 mJ/cm², repetition rate: 100 Hz, pulse duration: 15 ns; tested at COHERENT AG, München
** Fluence: 55 mJ/cm², repetition rate: 100 Hz, pulse duration: 15 ns; tested at COHERENT AG, München

KrF, XeCl, XeF Lasers (248 nm, 308 nm, 351 nm)