Which is better: prism or diffraction grating?
| Prism | Reflective Diffraction Grating | |||
|---|---|---|---|---|
| Dispersion Principle | Exploits differences in the material refractive index according to the wavelength | Exploits diffraction from a reflective surface with a regular grating structure. | ||
| Light Utilization Efficiency | High (Generally has high efficiency despite light losses from boundary reflection and absorption during transmission through the material. A single prism covers the range from 185 to 2500 nm.) |
|
Low (Light with the same wavelength is dispersed in several directions as higher-order light. High efficiency near the blaze wavelength.) | |
| Wavelength Dependency of Dispersion | Variable. High for UV; low fo visible to NIR light. | High and approximately constant. |
|
|
| Temperature Dependency of Dispersion | High (Effects of temperature on refractive index.) | Low (Deformation due to temperature.) |
|
|
| Higher-Order Light | None |
|
Yes (Requires higher-order light cutout filter.) | |
| Stray Light | Low |
|
High (Dispersion due to higher-order light and surface roughness. Modern diffraction gratings achieve comparatively low stray light.) | |
| Polarization | Low |
|
High | |
The prism and diffraction grating are typical dispersive elements. The table here shows their respective features. Due to their superior dispersion properties, diffraction gratings are often used in modern spectrophotometers. The prism achieves dispersion due to the difference in the material refractive index according to the wavelength. However, the diffraction grating uses the difference in diffraction direction for each wavelength due to interference.