Do the beams split by the beam splitter produce the same light

Beams split by a beam splitter are not identical; they differ in intensity, and depending on the type of splitter, they may also differ in polarization or phase.

Intensity Differences

A beam splitter divides the incident light into two beams according to a designed reflection/transmission (R/T) ratio. For example, a 50/50 splitter sends half the light in each direction, while other ratios like 70/30 or 85/15 are also common. This means the split beams generally have different optical power compared to the original beam and to each other if the splitter is not perfectly balanced .

Polarization Effects

The type of beam splitter determines how polarization is affected:

• Non-polarizing beam splitters aim to maintain the original polarization of the incident light in both transmitted and reflected beams, though minor deviations can occur .
• Polarizing beam splitters separate light into orthogonal polarization states: one beam is s-polarized (reflected) and the other is p-polarized (transmitted). In this case, the split beams have different polarization, so they are not identical to each other or to the original unpolarized light .

Phase Considerations

Beam splitters can introduce a phase shift between the transmitted and reflected beams. This is particularly important in interferometry, where the relative phase affects interference patterns. Even if the intensity is equal, the beams may differ in phase, making them optically distinct .

Wavelength and Coating Effects

Dielectric coatings can be wavelength-specific, meaning the split beams may have slightly different spectral characteristics if the incident light is broadband. Metallic coatings reflect broadly but absorb some energy, slightly reducing the total output power .

Summary

While a beam splitter divides a single input beam into two output beams, the resulting beams are generally not identical. Differences can include:

• Intensity (based on the R/T ratio)
• Polarization (especially for polarizing splitters)
• Phase (due to reflection/transmission properties)
• Spectral characteristics (depending on coatings) In practical terms, the split beams are related to the original light but are modified versions, and their properties must be considered in optical experiments or applications like interferometry, microscopy, or laser systems .