GERMANIUM ETALONS

GERMANIUM ETALONS

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Solid Germanium Etalons

Germanium etalons  have a high index (~4.0 depending on wavelength) that creates a reasonably high finesse without any coatings.  They also remain transmissive farther out into the infrared than silicon etalons, the germanium etalon will still provide a decent signal at a wavelength of 14um. The high temperature sensitivity of germanium is similar to silicon and can also be useful (or problematic).  These etalons are often used to monitor the wavelengths of tunable lasers (like lead salt or quantum cascade lasers) in the mid-infra red.  A portion of the output from your tunable laser is directed at the germanium etalon. As the laser is tuned, the transmission through the etalon is modulated with a spacing between transmission peaks equal to the etalon FSR. Because germanium is very temperature sensitive, the etalon is not very useful for determining the absolute wavelength, but by tracking the number of peaks from a reference, the relative wavelength can be determined quite accurately.

• Material: Germanium
• Wavelength range: IR 2.5um to 14um
• Wedge < 0.5 arc second*
• Clear aperture: 12.7mm
• Surface quality: 80/50 or better
• Surface figure: λ/10
• Diameter: 25.4
• Finesse and FSR are dependent on the wavelength
• If your etalons require coatings then we can use our fluid jet polishing system to reduce the wedge and increase the finesse