How does a beamsplitter work?

Beamsplitters: Function and Types

Beamsplitters are optical components used to divide a beam of light into two parts. They are a fundamental element in optical systems for directing light paths, and they are extensively employed in a variety of applications such as spectroscopy, laser systems, and optical metrology.

How Beamsplitters Work

A beamsplitter takes an incident light beam and separates it into two beams with designated ratios, commonly 50/50, but other ratios like 70/30, 90/10, and others are possible. The separation of light is typically achieved through reflection, transmission, or a combination of both. These optical devices are designed to work for specific polarization states, wavelength ranges, and incidence angles. Depending on the design, a beamsplitter can split light evenly or unevenly, and it can be designed to favor either the reflected or transmitted beam.

The basic principle of a beamsplitter involves coating an optical substrate with a thin-film stack that is engineered to reflect a portion of the incident light and transmit the other. The multilayer thin-film structures use interference effects to control the properties of the reflected and transmitted beams. Effective design takes into account anti-reflection coatings on the back surface to minimize losses and ghosting effects caused by secondary reflections.

Types of Beamsplitters

• Plate Beamsplitters: These are thin, flat glass with a coated surface that reflects part of the light and transmits the other. Their simple design makes them widely used in general optical applications.
• Cube Beamsplitters: Comprised of two right-angled prisms cemented together, cube beamsplitters have a dielectric coating on the hypotenuse of one of the prisms. They are robust and easier to mount without changing the optical path length.
• Polarizing Beamsplitters: These are designed to split light based on polarization states. The reflected beam contains light polarized in one direction, while the transmitted beam contains light polarized orthogonally to the reflected light.
• Dichroic Beamsplitters: They separate light by wavelength, reflecting certain wavelengths while transmitting others. They are essential in fluorescence microscopy and multispectral imaging.

In conclusion, beamsplitters are versatile optical components that by employing reflection, transmission, and interference, partition light beams into separate paths. Their variety and the specificity of their designs to requirements of polarization, wavelength, and application ensure that they are pivotal in scientific, industrial, and technological fields.