What is a Beamsplitter?

The primary function of a beamsplitter is to separate a single beam of light into two parts, one reflected and one transmitted. The incident light is split at the surface which is usually set at some angle so the reflected and transmitted beams are separated. Any metal layer that forms a partially reflective mirror can serve as a beamsplitter, and many under the “plate” category are no more sophisticated than that.

The two beams that split from the original incident light will normally have constant values over a specified wavelength range. These are called neutral beamsplitters. Other types separate colors with the transmitted and reflected beams displaying different parts of the visible spectrum or split the visible region from the infrared as is done with hot and cold mirrors. Beamsplitters also affect the polarization of the incident light and this property can be used to make effective polarizers.

Types of Beamsplitters

Plate Beamsplitters – Spectrally non-selective over the visible spectrum so that both split beams remain relatively neutral in color. Since there is very little light loss due to absorption, the sum of the reflected and transmitted beam intensity nearly equals that of the incident beam.

Polka-Dot Beamsplitters Provide a near constant reflection to transmission ratio from 250nm to over 2.0µm with minimal angle sensitivity. In production, micron-scale “polka-dots” of aluminum are deposited on the substrate. These polka-dots reflect the incident light, while the uncoated area allows the remaining light to transmit.

Dichroic Beamsplitters – Optimized to provide high transmission of one spectral band, while reflecting a second spectral band, with a very sharp transition slope between these two bands. Designed for use at 45° AOI.

Transmission Grating Beamsplitters Designed for the useful division of He-Ne lasers, and multiple laser line separation. The transmitted beam is split into multiple diffracted orders.

Importance of Quality Assurance

To meet the challenging application requirements in aerospace, defense, and healthcare they must undergo a number of critical testing procedures ranging from atomic force and optical microscopy to diffraction grating efficiency measurements and accelerated environmental testing. Dynasil’s manufacturing facilities are ISO 9001:2015 certified to ensure that our procedures and products meet the highest quality and performance standards.

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Beamsplitters – A Vanguard of Modern Technology