• Beamsplitter Coating on Front Surface: 250 - 450 nm
• Optimized for 50:50 Beamsplitting for a 45° Angle of Incidence (AOI)
• Antireflection (AR) Coating on Back Surface: 250 - 450 nm
• Ø1/2", Ø1", 25 mm x 36 mm, and Ø2" Versions Available
• UV Fused Silica Substrate 
• 30 arcmin Wedged Back Surface on Round Beamsplitters Minimizes Ghosting

Thorlabs' 50:50 UV Fused Silica Broadband Beamsplitters, which are available in Ø1/2", Ø1", 25 mm x 36 mm, and Ø2" versions, have a beamsplitter coating for the 250 - 450 nm range deposited on the front surface that has been optimized for a 45° angle of incidence. A dielectric coating provides long-term stability.

These plate beamsplitters utilize a UV-grade fused silica substrate, which offers high transmission deep into the UV (down to 185 nm), good homogeneity, and a lower coefficient of thermal expansion than N-BK7. In addition, UV fused silica exhibits virtually no laser-induced fluorescence (as measured at 193 nm), making it an ideal choice for applications from the UV to the near IR.

To help reduce unwanted interference effects (e.g., ghost images) caused by the interaction of light reflected from the front and back surfaces of the optic, all of these plate beamsplitters have an antireflection (AR) coating deposited onto the back surface. This coating is designed for the same operating wavelength range as the beamsplitter coating on the front surface. Approximately 4% of the light incident at 45° on an uncoated substrate will be reflected; by applying an AR coating to the back side of the beamsplitter, this percentage is reduced to an average of less than 1% over the entire operating range of the coating. In addition to this feature, the back of all of our round broadband plate beamsplitters has a 30 arcmin wedge; therefore, the fraction of light that does get reflected from this AR-coated surface will diverge.

Technical Specs

• • • • Item #	Size	Thickness	Wedge Angle	Split Ratio (R:T)	Overall Performance	Info
        BSW19	Ø1/2"	3.0 mm	30 arcmin	50:50	Tabs = 50 ± 12%, Rabs = 50 ± 12%, Tabs + Rabs > 99%, |Ts-Tp| < 40% and |Rs-Rp| < 40%, 45° AOI
        BSW20	Ø1"	5.0 mm	30 arcmin	50:50
        BSW20R	25 mm x 36 mm	1.0 mm	No Wedge	50:50
        BSW21	Ø2"	8.0 mm	30 arcmin	50:50