Features

• AR Coatings Customized for 45° AOI, with Broadband Wavelength Ranges:
  • 250 nm - 450 nm with <1.0% at 45° AOI
  • 350 nm - 1100 nm with <2.0% at 45° AOI
  • 400 nm - 700 nm with <1.0% at 45° AOI
  • 600 nm - 1700 nm with <1.5% at 45° AOI
  • 700 nm - 1100 nm with <1.0% at 45° AOI
  • 1200 nm - 1600 nm with <1.0% at 45° AOI
• Ø1" Round and 25 mm x 36 mm Rectangular Options
• Round Compensation Plates have 30 arcmin Back Surface Wedge to Minimize Ghosting
• UV Fused Silica Substrate (Transmission Curve)

These Beamsplitter Compensation Plates are designed for use in Michelson and other interferometers, and they are additionally ideal as 45° windows in optical enclosures. The substrate material of both the rectangular and wedged round versions of these beamsplitter compensation plates is UV fused silica. For best results when pairing a plate with beamsplitter, choose the two so that their substrate materials and thicknesses are the same. When these plates are used as 45° windows in optical enclosures, the 1.0 mm thick rectangular plates are preferred where space is limited and the wedged round plates when it is of interest to suppress ghosting.

As both surfaces of these beamsplitter compensation plates are antireflection (AR) coated for a 45° angle of incidence (AOI), they are optimally oriented at a 45° angle to the incident light. This is in contrast to our other UV Fused Silica AR coated wedged and flat windows that are designed to be used with their coated surfaces oriented normally to the incident light (0° AOI). The coated surfaces of the 25 mm x 36 mm x 1 mm rectangular versions are parallel with one another and perpendicular to the ground edge. The Ø1" round versions are 5 mm thick and feature a front surface that is perpendicular to the ground edge and a back surface that makes a 30 arcmin angle with the ground edge. The slight wedge on the back surface of the round plates causes any reflected light to diverge from the incident light path, which acts to suppress ghosting and fringe patterns that may arise from reflections.

UV-grade fused silica is well suited for applications that benefit from increased transmission deeper into the UV than N-BK7. UV fused silica also offers a lower index of refraction for a given wavelength, better homogeneity, and a lower coefficient of thermal expansion than N-BK7. Approximately 4% of the incident light is reflected from uncoated UV silica surfaces. The broadband AR coatings on these 45° AOI beamsplitter compensation plates reduce the average reflection to less than 1.0% to 2.0%, depending on the wavelength range of the coating.

When used in a Michelson or similar interferometer, the plate is paired with a beamsplitter as shown in the image above to compensate for the non-zero thickness of the beamsplitter. Placing the compensation plate between the beamsplitter and the fixed mirror essentially sandwiches the reflective surface of the beamsplitter between two equal thicknesses of glass, so that this composite beamsplitter contributes the same optical path length, dispersion, and other optical effects for both arms of the interferometer. Without the plate, light travelling the fixed mirror arm travels through a total of one third the thickness of glass as light travelling through the translating mirror arm.

In addition to the UV fused silica flat and wedged windows offered here, Thorlabs also offers flat and wedged windows with other substrate materials (see the selection guides below). Additionally, flat and wedged windows with custom sizes and thicknesses are available; please contact Tech Support for more information.