BS025

• 10:90 reflection-to-transmission ratio (R), directing approximately 10% of incident light into the reflected path and 90% into the transmitted path.
• Non-polarizing design minimizes polarization-dependent differences between the transmitted and reflected beams.
• 25.4 mm (1") cube size for integration into standard optical systems.
• Designed for the 400–700 nm visible wavelength range.
• Manufactured from N-BK7 optical glass for reliable visible-wavelength performance.
• BBAR-coated external surfaces with an average reflectance of <0.5% over the 400–700 nm coating range at 0° AOI.
• Large clear aperture: >20.3 × 20.3 mm.
• Low transmitted beam deviation: 0° ± 5 arcmin.
• High optical quality: 40-20 scratch-dig surface quality.
• Suitable for applications where the majority of the incident optical power needs to remain in the transmitted beam while a smaller portion is directed to a monitoring or secondary optical path.

The Thorlabs BS025 is a 10:90 (R) non-polarizing beamsplitter cube designed for optical systems operating within the 400–700 nm visible wavelength range.

The beamsplitter divides an incident optical beam into reflected and transmitted components, with approximately 10% of the optical power reflected and 90% transmitted. This asymmetric splitting ratio makes the BS025 particularly useful when a small portion of the optical signal needs to be extracted for monitoring, measurement, alignment, or detection while preserving the majority of the optical power in the primary beam path.

The cube is manufactured from N-BK7 optical glass and features broadband antireflection coatings on its outer optical surfaces. The coating is designed for the 400–700 nm wavelength range, with an average reflectance of less than 0.5% at 0° angle of incidence.

As a non-polarizing beamsplitter, the BS025 is designed to provide similar behavior for different polarization states. Thorlabs specifies that the difference between the S- and P-polarized transmission and reflection is less than 10% across the 400–700 nm coating range.

The cube geometry also provides a convenient way to integrate the beamsplitter into free-space optical systems while maintaining a well-defined transmitted and reflected beam path.

Product Type: Non-Polarizing Beamsplitter Cube
Part Number: BS025
Cube Size: 25.4 mm (1")
Wavelength Range: 400–700 nm
Splitter Ratio (R): 10:90
Reflectance: 7% nominal, +10% / -5%
Transmittance: 87% nominal, ±10%
Substrate Material: N-BK7
Clear Aperture: >20.3 × 20.3 mm
Coating: BBAR, 400–700 nm
Average Reflectance: <0.5%, 0° AOI
Angle of Incidence: 0°
Transmitted Beam Deviation: 0° ± 5 arcmin
Reflected Beam Deviation: 90° ± 5 arcmin
Transmitted Wavefront Error: <λ/4 @ 633 nm
Surface Quality: 40-20 Scratch-Dig
Dimensional Tolerance: +0.0 / -0.2 mm
Approx. Weight: 41.1 g

The overall optical performance is specified over the 400–700 nm coating range at 0° AOI, with total transmission and reflection greater than 85%. The S- and P-polarization components are matched within 10% for both transmission and reflection.

The BS025 is suitable for a wide range of visible-wavelength optical and photonics applications, including:

• Laser Beam Monitoring
• Laser Power Sampling
• Beam Splitting and Beam Routing
• Optical Signal Monitoring
• Free-Space Optical Systems
• Laser Alignment Systems
• Optical Measurement Systems
• Imaging Systems
• Microscopy
• Spectroscopy
• Photodiode Signal Monitoring
• Scientific and Research Optical Setups
• Photonics and Quantum Optics Experiments

The 10:90 R ratio is particularly useful for applications where a small fraction of the beam is required for monitoring or measurement while approximately 90% of the optical power continues along the primary optical path. For example, the BS025 has been used in optical imaging systems to direct a small portion of a signal to a camera or photodetector while sending the majority of the light toward the primary detection or measurement system.