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KRS-5 is a medium refractive index material (2.37 @ 10 microns) with excellent long wavelength transmission in the infrared spectral region. It is non-hygroscopic with very good chemical resistance, but KRS-5 will occasionally exhibit strange and sometimes even bizarre cold flow behavior. Therefore it is not possible to polish flat. Pressure windows will “balloon” very slowly over time. The primary use is as an acid resistant window or ATR element or as a protective window for hygroscopic optical elements. It is extremely toxic and is absorbed through the skin and should only be handled with glove protection.
Melting point: 414.5 °C
Density: 5.65 g/cm3
Solubility in H2O: 0.05 g/100 g at 20 °C
Hardness: 40 kg/mm2
Appearance: Red clear
Far-IR Transmission – 1 mm thick KRS-5 window
Far-IR Transmission – 4 mm thick KRS-5 window
In the last few years several successful sampling devices have been manufactured by diamond turning KRS-5 and contacting it with diamond to construct a device with extreme durability and wavelength coverage.
Short Wavelength Range: 17,900 cm-1 (1 mm)
Long Wavelength Range: 204 cm-1 (1 mm), 232 cm-1 (4 mm)
KRS-5 can be coated with a BBAR (Broad Band Anti- reflection) coating. However, since KRS-5 will cold flow, this coating is much thinner than those on more stable substrate materials and therefore not as effective. Also, it will not improve transmission at wavelengths longer than 16 microns. KRS-5 may also be hard coated when used for wavelengths less than about 18 microns.
Short and Long Wavelength Ranges for which transmissivity is greater than 50% of stated crystal thickness.