Spectrometers
2024-3-24
Definition:
A device for recording spectra.
A spectrometer is an instrument used to record the spectrum of a light source. That is, it measures the power spectral density (PSD) of light as a function of wavelength or frequency. Not all spectrometers give calibrated PSDs; often the intensity is not calibrated and the calibration factor (responsivity) is wavelength dependent.
Using the spectral interference method, not only the power spectral density but also the spectral phase can be obtained.
Table of contents
Spectrometer using diffraction grating and prism
interference spectrometer
Spectrometer records spectral details
extreme spectral area spectrometer
Spectrometer using diffraction grating and prism
Many spectrometers use one or more diffraction gratings to obtain wavelength-dependent diffraction effects, or one or more prisms to obtain wavelength-dependent refraction. The incident light needs to be collimated before the beam enters the grating or prism. After passing through the dispersion device, components of different wavelengths propagate in slightly different directions. They then pass through some other optics and finally into the photodetector.
In a scanning spectrometer, the detector, which can be a photodiode or photomultiplier tube, is placed behind a narrow slit so that only a narrow range of wavelengths of light reaches the detector at a time. You can change the position of the slit, or the direction of the grating or prism to scan light in a specific wavelength range. It is assumed that the PSD of the incident light is unchanged during this time. The optical device then functions like a tunable monochromator. Figure 1 is the design diagram of a common Czerny-Turner monochromator. If the spectrum is very broad and the resolution of the scan is high, and if the detector response is not fast enough, the acquisition time of the entire spectrum will be very long.
Figure 1: Czerny-Turner monochromator design. The light entering the narrow slit is collimated by a curved mirror, then deflected by a diffraction grating as a function of wavelength, and then refocused by another curved mirror. For the case of a diffraction grating with a certain orientation, only a narrow range of wavelengths of light can pass through the exit slit. (The rays in the figure correspond to this wavelength range.) The entire device is housed in a box containing additional apertures and a black cover to minimize stray light.
A device for recording spectra.
A spectrometer is an instrument used to record the spectrum of a light source. That is, it measures the power spectral density (PSD) of light as a function of wavelength or frequency. Not all spectrometers give calibrated PSDs; often the intensity is not calibrated and the calibration factor (responsivity) is wavelength dependent.
Using the spectral interference method, not only the power spectral density but also the spectral phase can be obtained.
Table of contents
Spectrometer using diffraction grating and prism
interference spectrometer
Spectrometer records spectral details
extreme spectral area spectrometer
Spectrometer using diffraction grating and prism
Many spectrometers use one or more diffraction gratings to obtain wavelength-dependent diffraction effects, or one or more prisms to obtain wavelength-dependent refraction. The incident light needs to be collimated before the beam enters the grating or prism. After passing through the dispersion device, components of different wavelengths propagate in slightly different directions. They then pass through some other optics and finally into the photodetector.
In a scanning spectrometer, the detector, which can be a photodiode or photomultiplier tube, is placed behind a narrow slit so that only a narrow range of wavelengths of light reaches the detector at a time. You can change the position of the slit, or the direction of the grating or prism to scan light in a specific wavelength range. It is assumed that the PSD of the incident light is unchanged during this time. The optical device then functions like a tunable monochromator. Figure 1 is the design diagram of a common Czerny-Turner monochromator. If the spectrum is very broad and the resolution of the scan is high, and if the detector response is not fast enough, the acquisition time of the entire spectrum will be very long.
Figure 1: Czerny-Turner monochromator design. The light entering the narrow slit is collimated by a curved mirror, then deflected by a diffraction grating as a function of wavelength, and then refocused by another curved mirror. For the case of a diffraction grating with a certain orientation, only a narrow range of wavelengths of light can pass through the exit slit. (The rays in the figure correspond to this wavelength range.) The entire device is housed in a box containing additional apertures and a black cover to minimize stray light.
