Dispersing prism

equilateral prism is a triangular optical prism whose three faces are equal in width and whose three apex angles are all 60°. It is the most common type of dispersing prism used in optics and spectroscopy.

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Description

When a beam of white light enters one face, it is refracted at both the entrance and exit surfaces. Because the refractive index of the glass varies with wavelength (dispersion), different colors are bent by different amounts and emerge spatially separated, forming a spectrum. Minimum deviation occurs when the ray passes symmetrically through the prism (the angle of incidence equals the angle of emergence), which is the condition used for measuring a material's refractive index and Abbe number.

Equilateral prisms are widely used in demonstration and teaching of dispersion and total internal reflection, in spectrometers and monochromators, in wavelength-separation setups, and as beam-steering or turning elements. They are commonly made from optical glasses such as BK7 (N-BK7) or fused silica, and occasionally from higher-dispersion glasses like F2 or SF11 when strong dispersion is required.

Parameter	Value
Material	N-BK7 (or fused silica, F2, SF11 on request)
Apex angle	60° ± 3 arcmin
Surface quality	60/40 scratch-dig (standard), 40/20 available
Surface flatness	λ/4 per face at 632.8 nm
Clear aperture	≥ 80% of face dimension
Dimensional tolerance	±0.1 mm
Angle tolerance	±3 arcmin
Refractive index (n_d, 587.6 nm)	1.5168
Abbe number (V_d)	64.17
Refractive index homogeneity	1×10⁻⁵ (standard), 5×10⁻⁶ (precision)
Coating	Uncoated (standard); AR coating on request
Edge/wavelength range	350–2000 nm (BK7 transmission)
Bevel	Protective bevel on edges
Face dimensions (common sizes)	10, 12.7, 20, 25, 25.4, 30, 50 mm
Minimum deviation (n=1.5168)	≈ 38.6°

Can be customized according to your requirements

Dispersing prism

Dispersing prism

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