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Germanium Crystal

POC-OC-122478- Germanium Crystal

  • High optical transmission in the 2–12 μm infrared range.
  • Excellent mechanical strength and thermal conductivity.
  • Low absorption at 10.6 μm, ideal for CO₂ laser optics.
  • Insoluble in water, ensuring stable and durable operation.
  • Suitable for infrared imaging systems, spectrometers, and ATR applications.

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General Description

Germanium Crystal (Ge) is a chemically inert optical material with excellent transmission in the infrared spectral range of 2–12 μm. Its high hardness and thermal conductivity make it a preferred choice for demanding applications, including infrared thermal imaging systems, spectrometers, and CO₂ laser optics. With a minimal absorption at 10.6 μm, Germanium Crystal is ideal for use in CO₂ laser windows and output coupling mirrors. It also serves as a base material for infrared filters, including anti-reflective (ATR) applications. Germanium’s high refractive index allows it to operate efficiently in 50% beam-splitting systems without the need for additional coatings.

General Applications

Germanium Crystals are widely used across a range of applications:

  • Infrared Thermal Imaging Systems: Germanium windows provide high optical performance in thermal imaging devices, offering efficient infrared transmission for precise imaging results.
  • Spectrometers and Analytical Instruments: Used in infrared spectrometers due to its broad transmission spectrum and thermal stability.
  • CO₂ Laser Optics: Germanium is extensively applied in CO₂ laser systems as windows, lenses, and output coupling mirrors due to its low absorption at 10.6 μm.
  • Infrared Filters and ATR Lenses: Its high refractive index and low dispersion make Germanium ideal for ATR lenses and beam-splitting filters.
  • Aerospace and Defense: Germanium optics are utilized in advanced infrared surveillance and targeting systems due to their durability and optical properties.

Chemical and Structural Properties

Property Value
Density 5.33 g/cm³
Hardness Mohs scale: 6–6.5
Thermal Conductivity 59 W/m·K
Thermal Expansion Coefficient 5.8 × 10^-6 /°C
Melting Point 937°C
Crystal Structure Diamond Cubic
Cleavage Plane <111>
Common Crystal Orientation <111>, <100>, <110>

Optical Properties

Property Value
Transmission Range 2–12 μm
Refractive Index n = 4.002 (at 10.6 μm)
Absorption Coefficient <0.027 cm^-1 at 10.6 μm
Reflective Loss 53% (both surfaces, uncoated)
dn/dT (Thermal Coefficient) 396 × 10^-6 /°C
Lattice Constant 5.658 Å

Standard Fabrication Specifications

Specification Value
Surface Flatness λ/4 @ 632.8 nm
Surface Quality 40-20 scratch-dig
Clear Aperture >90%
Chamfer <0.25 mm × 45°
Length Tolerance ±0.1 mm
Thickness Tolerance ±0.1 mm
Parallelism <1′

Spectrum Transmission Curve

Germanium Crystal demonstrates excellent transmission from 2 μm to 12 μm, with very low absorption losses around 10.6 μm. Transmission efficiency improves significantly with anti-reflective (AR) coatings.

POC-Germanium Crystal Spectrum Transmission Curves

Coating Specification

  • AR Coating: Enhances transmission in the 2–12 μm range.
  • Custom Coatings: Available upon request for specific laser wavelengths, such as 10.6 μm for CO₂ laser optics.
  • Adhesion Test: Compliant with MIL-C-675C military standards, an adhesion test involved applying a tape that meets LT-90 specifications onto the lens film layer. The tape was affixed fully and then removed vertically. This procedure was performed three times, resulting in no blistering or peeling.
  • Temperature Test: In line with MIL-C-675C specifications, test pieces were subjected to temperatures of -62±1℃ and 71±1℃. After maintaining them at room temperature (16℃~32℃) for two hours, the adhesion test was repeated, confirming no film detachment.
  • Abrasion Resistance Test: Conforming to MIL-C-675C and CCC-C-440 standards, the abrasion resistance test involved a gauze tester applying a minimum force of 1.0 lbs (0.45 kg) to the film. This was repeated 25 times with gauze widths of 1/4 inch (6.4mm) and 3/8 inch (9.5mm), ensuring no damage occurred to the film surface.
  • Humidity Test: Under MIL-C-675C criteria, the test piece was placed in a controlled temperature and humidity chamber set to 49 ±2℃ and 95%~100% humidity for 24 hours. The film remained intact, with no peeling, scratches, or other defects.
  • Solvent and Cleaning Testing: Following MIL-C-675C specifications, test pieces were exposed to room temperature conditions (16℃~32℃) and tested with acetone and alcohol for at least 10 minutes each. After air drying and subsequent cleaning with a cotton cloth soaked in alcohol, the film surface showed no signs of peeling or scratches.
  • Salt Spray Test: After 100 hours in a 35°C environment with a 5% saltwater concentration, the film showed no signs of damage.
Dimensions (mm) Coating Price (USD) SKU
25 × 2 AR @ 10.6 μm 150 GE25AR
50 × 5 AR @ 10.6 μm 280 GE50AR
75 × 10 AR @ 10.6 μm 450 GE75AR
Custom Size On request On request CUSTOM

POC-OC-122478- Germanium Crystal

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