OP-5483 Solid Germanium Etalons

Germanium; 2.5-14 µm; Finesse Dependent on Wavelength; FSR Dependent on Wavelength; Thickness 25.4-50.8 mm; Uncoated; Dia 25.4 mm; Clear Aperture Dia. 12.7 mm

LightMachinery’s OP-5483 series of solid Germanium (Ge) etalons are high-index components for longer IR wavelengths. OP-5483 series etalons are manufactured using the company’s patented fluid jet polishing (FJP) technology – allowing the adjustment of the etalon’s shape and flatness to within a few nanometers. This series of thick Germanium etalons is available with a diameter of 25.4 mm and lengths of 25.4, 38 and 50.8 mm.

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 and will still provide a decent signal at a wavelength of 14 µm. 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-infrared. 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’s FSR. As Germanium is very temperature sensitive, OP-5483 series etalons are 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.

Etalons are optically transparent, flat components with very precisely parallel reflecting surfaces. For high performance (i.e. resolution), these components require very high-quality, flat and level surfaces with low roughness and extreme parallelism. Solid Germanium etalons are comparatively simple, robust, yet very parallel optical components with a wide variety of applications in lasers and spectroscopy.

Although solid etalons are generally coated to increase the finesse of the etalon, uncoated solid etalons like the OP-5483 series – using only the 4% fresnel reflection to provide the etalon effect –are often used inside laser cavities since only low finesse is required to filter out unwanted laser wavelengths, and uncoated etalons are very damage resistant.

One major issue with solid etalons is their instability to temperature changes (both the index and the physical thickness of the etalon material change with temperature), which can be unacceptable in certain applications. In those cases, please refer to air spaced etalons that reduce this problem of temperature dependence by using air as the etalon medium. In certain applications though, the temperature dependence can also be a useful method for tuning the transmission peak position since it effectively changes the thickness of the etalon.

Sometimes you need something special – if you are looking for a customized solid Germanium etalon that exactly meets your specific requirements, please get in touch with the AMS Technologies etalon experts. Our supplier LightMachinery is extremely experienced with specifying, designing and manufacturing custom etalons using the company’s patented fluid jet polishing (FJP) technology. We are looking forward to discussing your customized etalon solution!

Fluid jet polishing (FJP) systems use a fine stream of slurry to accurately remove nanometers of material from an optical surface. Many years of refining this computer controlled polishing technology have enabled LightMachinery to use FJP for the adjustment of the shape and flatness of optical components such as etalon mirrors to within a few nanometers as well as the production of very thin components such as wafers and thin etalons that are impossible to accurately polish using conventional technology.

Key Features:

• Etalon Material: Germanium
• Wavelength Range: 2.5 to 14 µm (Infrared, IR)
• Finesse: Dependent on Wavelength
• Free Spectral Range, FSR: Dependent on Wavelength
• Uncoated
• Diameter: 25.4 mm (1”)
• Length: 25.4, 38, 50.8 mm
• Clear Aperture: Diameter 12.7 mm
• Surface Figure: λ/10
• Surface Quality: 80/50 or Better
• Wedge: <0.5 arcsec – If Coating is Required, Wedge Can Be Reduced and Finesse Can Be Increased

Applications: Spectroscopy; Lasers; Interferometers; Wavelength Measurement; Fine-structural Investigation of Spectral Lines