Germanium (Ge) Window

Germanium (Ge) Window

Germanium (Ge) window is provided for infrared (IR) transmission. Ge window is not transparent for visible lingt and UV light while has a wide transmission range in infrared band. Infrared grade germanium single crystal is the basic material for making infrared lenses, infrared window and other optical components. A specification of Ge widow buy from PAM-XIAMEN, one of germanium window suppliers, is shown below:

Germanium Window

1. Ge Window Specifications


1. Germanium, 5mm width x length 30mm x 1mm thick
As-cut wafer, s/d: 60/40
Resistivity: 5-40


2. Germanium Window :
Vertical = 158.00 mm
Horizontal = 120.00 mm
Thickness = 8.40 mm

3. IR Window (Germanium) :
Vertical = 120.00 mm
Horizontal = 120.00 mm
Thickness = 6.25 mm

The important parameters of the germanium optical window are light transmittance, surface accuracy, thickness, parallelism, substrate material and other properties. According to the specific application, you can choose the window film with suitable parameters.

2. Germanium Optical Properties

The IR optical window with 2~16 um uncoated region has a good transmission and very low peak absorption. Therefore, germanium single crystal is an ideal solution for the carbon dioxide laser cavity. There is a strong opacity of Ge material in the whole visible spectrum. This characteristic makes it possible for applications of IR wavelength, like low power CO2 laser. Moreover, the low dispersion characteristic makes germanium ideal for imaging applications.

The refractive index of germanium material is very high, which is approximately 4.0 in the 2-14μm band. When germanium as an infrared window material, it can be coated as needed to increase the transmittance of the corresponding band. If one side AR coated, the transmission rate would be >61%; if the transmission rate >90%, it should be used double side coating. Figure below shows transmission rate of double side polished AR coated wafer: 

transmission rate of double side polished AR coating

Ge Transmission Rate

Meanwhile, the transmission of germanium window is extremely sensitive to temperature. Transmission rate is decreased when the temperature goes up. Therefore, Ge window can only be used below 100°C. The germanium density of 5.33g/cm3 should be taken into account in the system design with strict weight requirement. In addition, the Knoop hardness of Ge is 780, which is about twice the hardness of magnesium fluoride, which makes it more suitable for applications in the IR field of changing optics.

3. Applications of Germanium Window

The window is used to separate the environment on both sides, such as separating the inside and the outside of the instrument, so that the inside and the outside of the instrument are isolated from each other, thereby protecting the internal components. Ge window can be used in the field of optoelectronics, infrared thermal imaging cameras, infrared laser systems, infrared optical instruments, and has an important application in semiconductors, solar cell, aerospace measurement and control, optical fiber communications, infrared optics, chemical catalyst, biomedicine, nuclear physics detection, etc.


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