What are the functions of a prism?
Release Time：
2025-05-15
outline： A prism is a polyhedral optical element made of an optically transparent material (such as glass, crystal, fused quartz, etc.). It controls light through refraction, reflection, dispersion, or polarization effects and is widely used in optical instruments, communications, scientific research, and laser technology.
A prism is a polyhedral optical element made of optically transparent materials (such as glass, crystal, fused quartz, etc.). It controls light through refraction, reflection, dispersion, or polarization effects and is widely used in optical instruments, communications, scientific research, and laser technology. The following are its core functions and typical application scenarios:
I. Spectral Dispersion: Decomposing composite light into monochromatic light
The dispersion features of a prism (different wavelengths of light have different refractive angles) make it a core component for spectral dispersion, commonly used in spectral analysis and astronomical observation.
1. Spectrometers and Monochromators
Principle: After incident polychromatic light, light of different wavelengths is "spread" into a spectrum due to differences in refractive index (e.g., Newton used a triangular prism to decompose sunlight into seven colors).
Applications:
Analyzing the composition of substances in scientific research (e.g., atomic emission spectrometers);
Observing stellar spectra in astronomical telescopes to infer their elemental composition and motion state.
2. Laser Spectroscopy and Wavelength Selection
In laser systems, prisms can separate lasers of different wavelengths (e.g., beam selection of multi-wavelength lasers) or select a single wavelength output by adjusting the angle of incidence.
II. Light Path Steering and Folding: Changing the direction of light propagation
Using the reflective surface of the prism (coated with a reflective film or total internal reflection effect) to change the direction of the optical path, replacing traditional mirrors, it has higher stability and anti-interference ability.
1. Total Internal Reflection Prisms (No Film Reflection)
Right-angle prism:
Function: Deflects the optical path by 90° or 180° (as shown in Figure 1), often used in periscopes and microscope reflectors.
Advantages: Total internal reflection efficiency is close to 100%, superior to ordinary mirrors (which have absorption losses).
Dove Prism:
Function: Rotates an inverted image without changing the direction of light propagation, used for image correction in optical systems (e.g., correcting the inverted image in a telescope).
2. Reflective Prism Combinations (Complex Optical Path Folding)
Schmidt-Pechan Prism:
Function: Achieves a 180° turn of the optical path and inverts the image, compact design used in SLR camera pentaprism viewfinders, allowing the photographer to see a correct image.
Amici Roof Prism:
Function: Folds the optical path in a telescope and corrects the left-right inversion of the image, widely used in binoculars (e.g., Porro prism system).
III. Polarized Light Control: Separating or Rotating Polarization States
Some prisms utilize the polarization features of birefringent crystals (such as calcite) to control polarized light.
1. Polarizing Beamsplitter (PBS)
Principle: Using the birefringence effect of crystals, the incident light is divided into two beams of linearly polarized light with perpendicular vibration directions (such as o-light and e-light).
Applications:
Separating left and right eye polarized light in 3D projectors;
Splitting light and maintaining pure polarization state in laser interferometers (e.g., the polarization splitting module of a Michelson interferometer).
2. Soleil-Babinet Compensator
Function: By adjusting the optical path difference of two movable birefringent prisms, it realizes the mutual conversion between elliptical polarized light and linearly polarized light, used for polarization state measurement or compensation.
IV. Beam Shaping and Homogenization: Controlling the Spot Shape
Prisms can adjust the divergence angle and cross-sectional shape of the beam to meet the needs of special optical systems.
1. Beam Expansion and Contraction
Galileo prism pair:
A combination of two wedge prisms can laterally shift the beam or change the beam divergence angle, used in laser beam expansion systems (e.g., adjusting the beam diameter at the laser radar emission end).
2. Beam Homogenization (Eliminating Gaussian Distribution)
Multiple prism combinations (such as microlens arrays) disrupt the intensity distribution of the Gaussian beam through multiple refractions, achieving spot homogenization, used in lithography, laser processing, and other scenarios requiring flat-top spots.
V. Special Function Prisms: Customized Optical Control
1. Cube Corner Prism
Structure: Three mutually perpendicular reflecting surfaces (similar to the vertices of a cube).
Function: Reflects the incident light back in the original direction (the optical axis parallelism remains unchanged), used in laser ranging (e.g., lunar laser ranging reflectors), and optical displacement sensors.
2. Dispersion Compensation Prism Pair
In fiber optic communication, the dispersion features of the prism are used to compensate for the group velocity dispersion (GVD) of the optical signal in the optical fiber, restoring the signal pulse width and improving the transmission distance.
3. Gradient Index Prism
The refractive index inside changes gradually, which can achieve a focusing effect similar to that of a lens, but with a more compact size, used in integrated optical devices or miniature optical systems.
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