transmittance of silicon

transmittance of silicon

The optical properties of silicon measure at 300K 1. One can see that in the 3-5 µm range, typically used in pyrometry and thermography, (and even to 6.5 µm) the transmittance dependence on thickness is not substantial. The purity of HiTranTM silicon eliminates all extrinsic impurity related absorption over the entire infrared band. In Fig. Lattice absorption, as well as Oxygen absorption, depends on the optical pass of radiation inside the element (roughly on element thickness). Maximal dimensions for crystals used for the optics production are as follows: According to the formula       ,       where ε0 = 11.67 is static permittivity, refractive index of silicon approaches 3.416 as wavelength goes to infinity (to 1000 µm and more in our case). Figure 2. It does not depend on resistance. Three grades of silicon are produced to optimize transmission in the operation wavelength region: Optical Czochralski Silicon (OCz-Si), Float Zone Silicon (FZ-Si), and High Resistivity Float Zone Silicon (HRFZ-Si). Doping is usually Boron (p-type) and Phosphorus (n-type). We note here that starting at 21 µm there is no difference in transmission between FZ-Si and OCz-Si with equal resistance and conductivity type. Intrinsic lattice vibrations in silicon reduce the transmission of infrared light THz beam expanders are meant to expand or converge parallel THz beams. Silicon has a further pass band 30 to 100 microns which is effective only in very high resistivity uncompensated material. Optical Silicon is generally lightly doped ( 5 to 40 ohm cm) for best transmission above 10 microns. Due to much less Oxygen concentration (10E16 cm-3 vs. about 10E18 cm-3 in OCz-Si) FZ-Si is free of Oxygen peaks and can be used for more critical applications. Sample thickness is 5 mm. Arrows point to the Oxygen absorption peaks. Holographic Notch and Narrow Notch Filters, Germanium Windows and Lenses for Thermography, Protective IR Windows for Unmanned Aerial Vehicles (UAV), Hardware-Software Complex for Operating Golay Detectors, THz Impulse Radiation Electro-Optical Detector, High Precision Astronomical Mirrors and Systems, Optical Coatings for Visible and Near IR Spectral Range, Copyright and Terms of Use of the Website Materials, Specific heat capacity (solid), J/(kg x °C), Thermal coefficient of refractive index @ 25°C. Materials with the resistance to 30 kOhm x cm are available. Silicon transmission, 16-1000 µm. Transmission in Far Infrared spectral region is shown in Fig. For longer wavelengths absorption becomes significant and transmission is strongly affected by thickness. Figure 1. Sample thickness is 5 mm. Figure 3. Silicon transmission in the 1 - 25 µm spectral range. OCz-Si has additional peaks at 5.8 µm, 9.1 µm, and 19.4 µm induced by Oxygen vibration absorption. Usually silicon is considered as the material of choice for systems operating in the Middle Infrared (MIR) region, from 3 to 5 µm. While a wide range of wavelengths is given here, silicon solar cells typical only operate from 400 to 1100 nm. 2 the transmission spectra for several thickness values are shown. Therefore, thickness is a very critical parameter for silicon usage in the range of 6 - 25  µm. Main principles of proper material choice are described and demonstrated below. production technology, conductivity type, and resistance) to guarantee the best transmittance. In Fig.1 transmission spectra in NIR (Near Infrared) and MIR ranges are shown. High Transmission (HiTranTM) silicon has unique transmission performance across most of the infrared band including the far infrared region. Lattice absorption, as well as Oxygen absorption, depends on the optical pass of radiation inside the element (roughly on element thickness). Transmission of OCz-Si and FZ-Si with respect to thickness. However silicon windows with thickness less or about 1 mm can also be successfully used in the second "atmosphere window" 7-14 µm. Samples thickness - 5 mm. Arrows point to  the Oxygen absorption peaks. 3. To avoid this, Silicon can be prepared by a Float-Zone (FZ) process. It is available in tabulated form from pvlighthouse as text and in graphical format. Silicon transmission in the 1 - 25 µm spectral range. We use crystals of appropriate grade (i.e. But in fact the material may be used in much broader operating range - from 1.2  µm to 1000  µm or even higher. For such applications (50 µm and more) Tydex offers HRFZ-Si maintaining 50-54% transmission to 1000 µm (and for longer wavelengths on custom request). There is a more up to date set of data in Green 2008 2. Also, all grades have phonon absorption peaks stipulated by lattice absorption in the 6.5 to 25 µm range. The choice of these grades depends on the wavelength range, element thickness and specific application. In this range average transmission of a OCz-Si window with thickness 0.5 mm exceeds 51%, and for FZ-Si it is a bit higher (about 51.9%) due to absence of the Oxygen absorption line. For 5 mm thick OCz-Si sample average transmission over the 8-10 mm band is less than 32% (for FZ-Si - about 38%) and only 18% over the 10-14 µm band (the same for both OCz-Si and FZ-Si). Also note that the transmittance does not depend on the crystal orientation. It does not depend on resistance. One can see that in 3 to 5 µm range practically there is no difference in transmission of materials of all used grades and resistances.

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