Front Surface Silver Mirrors (400 – 4000 nm)

Broadband Silver Mirrors for the VIS and NIR

Fig.1:Reflectance spectra of three standard types of protected silver mirrors:

a)Optimized for 600 – 1000 nm with R > 98 %

b)Optimized for 600 – 2000 nm, 600 – 750 nm with R > 96 %, 750 – 2000 nm with R > 98 %

c)Optimized for 1000 – 10 000 nm with R > 98 %

Optical Properties

R > 98 % throughout the specified wavelength range (except Fig. 1b)
R = 94 … 97 % in the VIS outside the specified wavelength range
R > 97 % in the NIR outside the specified wavelength range

Special Features

Silver has the highest reflectance of all metals in the VIS and NIR
Sputtered protective layers yield very stable optical parameters
Lifetime of more than 10 years in normal atmosphere has been demonstrated although unprotected silver is chemically unstable
The high atomic density of sputtered coatings guarantees that even very thin protective layers (≈ 20 nm) provide a good protection against the atmosphere
The thickness of the protective layer can be used to optimize the reflectance of the mirrors for different wavelength ranges (see Fig. 1)
Sputtered silver mirrors show extremely low scattering losses. (total scattering TS ≈ 30 ppm in the VIS and NIR)
Silver mirrors with defined transmittance (e.g. T = 0.01 %) on request (see Silver Mirrors for Ultrafast Lasers (550 – 1100 nm) f.)
Mechanical stability of protected silver mirrors is tested according to MIL-M-13508C § 4.4.5
Maximum diameter: 600 mm, especially for astronomical applications

Silver Mirrors for Use in Ultrafast Lasers

Fig.2:Reflectance and GDD spectra of a silver mirror optimized for use with ultrafast lasers in the wavelength range 600 – 1000 nm (AOI = 45°)

a)Reflectance vs. wavelength

b)GDD vs. wavelength

Silver mirrors are ideal in ultrafast laser systems because of their extremely broad low-GDD reflectance band. For more examples see page Silver Mirrors for Ultrafast Lasers (550 – 1100 nm).

Silver Mirrors with Enhanced Reflectance

The reflectance of silver mirrors can be enhanced for selected wavelengths or wavelength regions by a dielectric protective coating. Fig. 3 to Fig. 5 show examples for silver mirrors with enhanced reflectance. Such mirrors combine very high reflectance at the wavelengths of interest with a relatively high reflectance throughout the VIS which makes them ideal for use in conjunction with alignment lasers.

Mirrors for Astronomical Applications

Fig.3:Reflectance spectra of an enhanced silver mirror which shows R ≥ 98 % throughout the visible spectral range:

a)AOI = 0°

b)AOI = 45°, unpolarized light

Fig.4:Silver mirror with enhanced reflectance at 425 and 850 nm
(R > 99.5 %)

Turning Mirrors for 1030 nm

Fig.5:Silver based turning mirror with enhanced reflectance for 45°, 1030 nm and R > 80 % for any alignment laser in the red spectral range

The mirror in figure 5 is a cost-effective alternative for all dielectric mirrors for high power Yb:YAG or Nd:YAG lasers.

LIDT Info
50 kW/cm², wavelength: 1030 nm, cw
tested without destruction

Scanning Mirrors

Fig.6:Reflectance spectra of a dielectrically enhanced silver mirror which can be used as scanning mirror for laser diodes in the NIR:
HRu (22° – 58°, 805 – 940 nm) > 99.3 %
+ Ru (22° – 58°, 630 – 670 nm) > 50 %

For more information on enhanced silver mirrors see page High Power Lasers on the Basis of Yb- and Nd-doped Materials (1020 – 1080 nm), Silver Mirrors for Ultrafast Lasers (550 – 1100 nm) and Broadband and Scanning Mirrors (300 – 2500 nm).

Front Surface Silver Mirrors (400 – 4000 nm)