Which dispersive element yields non-linear dispersion and is used for higher frequency light?

Which dispersive element yields non-linear dispersion and is used for higher frequency light?

• A. Prism
• B. Diffraction grating
• C. Interference filters
• D. Glass filters

Answer: (A)

Dispersion arises because a material’s refractive index depends on wavelength. A prism shows nonlinear dispersion because n(λ) changes with wavelength in a non-simple way. When light passes through a prism, shorter wavelengths (higher frequency) experience a larger change in speed and bend more than longer wavelengths, and the relationship between wavelength and deviation isn’t a straight line. This makes the spectrum spread in a curved, nonlinear way, and it’s especially effective for separating the higher-frequency end of the spectrum. Diffraction gratings separate light by interference, and while there is wavelength dependence, the angular dispersion is more uniform over typical ranges, so the dispersion tends to be closer to linear within practical limits. Interference filters and glass filters don’t really disperse light into a spectrum; they mainly transmit or block certain wavelengths, so they don’t produce the spread you get from a prism.

Dispersion arises because a material’s refractive index depends on wavelength. A prism shows nonlinear dispersion because n(λ) changes with wavelength in a non-simple way. When light passes through a prism, shorter wavelengths (higher frequency) experience a larger change in speed and bend more than longer wavelengths, and the relationship between wavelength and deviation isn’t a straight line. This makes the spectrum spread in a curved, nonlinear way, and it’s especially effective for separating the higher-frequency end of the spectrum.

Diffraction gratings separate light by interference, and while there is wavelength dependence, the angular dispersion is more uniform over typical ranges, so the dispersion tends to be closer to linear within practical limits. Interference filters and glass filters don’t really disperse light into a spectrum; they mainly transmit or block certain wavelengths, so they don’t produce the spread you get from a prism.