At present, diffraction gratings are mostly used to replace the traditional prisms in the spectroscopic devices. Please explain in detail why diffraction gratings will replace prisms.

The fundamental reason why the spectrometer uses grating instead of prism is that the spectrum obtained by grating spectrometer has good quality and high signal-to-noise ratio.

There are two physical parameters to characterize the performance of spectrometer:

One: Spatial resolution

1. dispersion: To put it bluntly, it means how much different wavelengths can be separated.

2. Spectral purity: that is, how wide the slit image is.

3. Resolution: the ability to distinguish two adjacent spectral lines. And R =λ/δλ/Δ λ, Δ λ represents just two spectral lines that can be separated.

Two: dark source detection capability

1. Spectral illumination: it is the light intensity hitting the CCD.

2. Light transmittance: expressed by t, indicating the ability of the spectrometer to collect and transmit light. The greater the T, the greater the luminous flux passing through the light splitting system and the clearer the spectrum.

Among them, the product of transmittance t and resolution r, referred to as TR for short, is a characteristic quantity to measure the quality of spectrometer system, which has high TR, high resolution and hyperspectral quality.

From the resolution point of view, both prism spectrometer and grating spectrometer can achieve high resolution, but grating spectrometer can achieve high TR, that is, both high resolution and large luminous flux. Because astronomical targets are generally dark, grating spectrometers are widely used. On other occasions, prism spectrometer is still widely used because of its low cost.