A beam splitter cannot be completely "stopped" in the sense of halting its optical function, but its light transmission and reflection can be controlled, minimized, or redirected using variable splitters, polarization techniques, or absorptive materials.

Controlling Light Through a Beam Splitter

Beam splitters are designed to divide an incident light beam into transmitted and reflected components, either at a fixed ratio or, in some designs, a variable ratio . While you cannot stop the splitting action entirely, you can adjust the distribution of light:

• Variable beam splitters: Some beam splitters allow continuous adjustment of the reflected and transmitted power. This is often achieved using a rotating disk with a gradient coating or a rotatable half-wave plate combined with a polarizing beam splitter, which changes the polarization of the input beam and thus the power distribution according to Malus' law .
• Polarization control: By aligning the polarization of the incoming light with the axes of a polarizing beam splitter, you can direct nearly all light into one output port, effectively "stopping" light from exiting the other port .

Minimizing Unwanted Beams

In practical optical setups, secondary reflections or ghost beams can be problematic. Techniques to reduce or eliminate these include:

• Absorptive coatings or blackened surfaces: Applying matte or glossy black paint to edges or surfaces can absorb stray light and reduce veiling glare .
• Cross-polarization: Using polarizers in combination with the beam splitter can absorb or redirect unwanted secondary beams .
• Antireflection coatings: Applying AR coatings to non-silvered surfaces minimizes internal reflections and ghosting .
• Pinhole or aperture placement: Strategically placing apertures in front of the beam splitter can block divergent light that contributes to glare .

Summary

While a beam splitter inherently splits light and cannot be completely "stopped," you can control, redirect, or minimize the light using variable splitters, polarization techniques, absorptive coatings, or optical apertures. These methods allow precise management of light paths in interferometers, microscopes, cameras, and laser systems, effectively achieving the desired control over the beam splitter's output .