Beam splitter receives and emits light

A beam splitter receiving light at -13° will partially reflect and partially transmit the beam, with the exact splitting ratio and polarization effects depending on the type of beam splitter and its coatings.

Angle of Incidence Effects

Beam splitters are typically designed for a 45° angle of incidence (AOI), which optimizes the intended reflection/transmission ratio for standard coatings . When light strikes at -13°, the effective AOI is significantly different from the design value, which can lead to:

• Altered splitting ratio: The proportion of reflected versus transmitted light may deviate from the nominal 50/50 or specified ratio .
• Polarization dependence: Reflection and transmission coefficients vary for s-polarized (perpendicular) and p-polarized (parallel) light, and this effect becomes more pronounced at non-standard angles .
• Beam displacement: In plate beam splitters, the transmitted beam may be laterally shifted due to refraction, and the reflected beam may experience slight angular deviation .

Type of Beam Splitter Considerations

• Plate beam splitters: A thin glass plate with a coated surface; sensitive to AOI changes, which can cause ghost reflections and variations in the transmitted/reflected power .
• Cube beam splitters: Two prisms cemented together; more robust to small AOI deviations, but coatings are still optimized for a specific angle .
• Polarizing beam splitters: Designed to separate s- and p-polarized light; a -13° incidence may reduce extinction ratio and affect polarization purity .
• Variable or rotatable beam splitters: Some systems allow adjustment of the splitting ratio by rotating a waveplate or disk, which can compensate for non-standard AOI .

Practical Implications

Using a beam splitter at -13° instead of its design angle may result in unequal beam intensities, increased polarization-dependent losses, and slight beam misalignment. For high-precision applications, it is recommended to either:

• Use a beam splitter designed for the specific incident angle, or
• Adjust the system to maintain the AOI close to the design value to preserve the intended splitting ratio and polarization characteristics . In summary, a -13° incident angle is feasible, but the optical performance will differ from the nominal design, and careful consideration of the type of beam splitter and its coatings is necessary to predict the exact behavior.