Thorlabs' Ø1/2" and Ø1" Silicon (Si) Plano-Convex Lenses are available with a broadband AR coating optimized for the 3 - 5 μm spectral range deposited on both surfaces. This coating greatly reduces the high surface reflectivity of the substrate, yielding an average transmission in excess of 97% over the entire AR coating range. See the Graphs tab for detailed information.
Silicon offers high thermal conductivity and low density. However, since it has a strong absorption band at 9 microns, it is not suitable for use with CO2 laser transmission applications.
Plano-Convex lenses have a positive focal length and approach best form for infinite and finite conjugate applications. These lenses focus a collimated beam to the back focus and collimate light from a point source. They are designed with minimal spherical aberration and have a focal length given by f= R/(n-1), where R is the radius of curvature of the convex portion of the lens and n is the index of refraction.
*Much like surface flatness for flat optics, spherical surface power is a measure of the deviation between the surface of the curved optic and a calibrated reference gauge, typically for a 633 nm source, unless otherwise stated. This specification is also commonly referred to as surface fit.
*Edge thickness given before 0.2 mm at 45o typical chamfer. **Measured at the design wavelength, 4 μm
Shown above is a graph of the theoretical percent reflectivity of the AR coating as a function of wavelength. The average reflectivity in the 3 - 5 μm range is <1.5%. The blue shading indicates the region for which the AR coating is optimized.
Shown above is a graph of the theoretical transmission of the AR-coated silicon plano-convex lens. The blue shaded region denotes the 3 - 5 μm spectral range where the AR coating is optimized. For this wavelength range, the measured transmission is in excess of 95%.
Total Transmission of Optic (Si Substrate + AR Coating)
The table below gives the approximate transmission of these optics for a few select wavelengths in the 3 - 5 μm range. To see an excel file that lists all measured transmission values for the 1.2 - 8.0 μm range, please click here. Please note that the transmission values stated for wavelengths outside of the AR coating range are approximate and can vary significantly by coating lot.
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LA8308-E
- Ø1/2" Si Plano-Convex Lens, f = 15.0 mm, AR-Coated: 3-5 µm
