How is the Raman spectrometer constructed?

A typical Raman spectrometer includes three main parts: excitation source, sampling system and detection system. After years of development, these three parts have various forms of realization. For example, the current most typical excitation source uses a laser, the detector uses a spectrometer, and the sampling system is realized by multi-sampling microscopic light paths or optical fiber probes.

Raman spectroscopy mainly measures the frequency shift of molecules, so an excitation light source with very good monochromaticity is particularly important. Lasers are currently an ideal excitation light source, but not all lasers are suitable for Raman excitation.

As a Raman excitation light source, its frequency needs to be very stable without modal jumps, and its line width needs to be as narrow as possible to ensure the quality of the Raman spectrum peaks. In addition, the excitation wavelength used in different applications needs to be considered. The shorter the wavelength of the laser, the higher the excitation efficiency, but for many organics, the wavelength is not the only factor to be considered.

Most organic compounds will produce some fluorescence interference due to the transition of high-energy electrons. Although fluorescence is a relatively weak signal, compared to the efficiency of Raman scattering (about 1/10^7), it still masks the Raman signal to a large extent. Short-wavelength visible laser wavelengths (such as 473nm, 532nm, etc.) are more used in the characterization of inorganic materials, such as carbon materials.

Raman scattering is a very weak signal, so a long integration time is often required to collect the required spectral signal. This makes the TE refrigeration of the spectral detector particularly important.For the detection of weak Raman signals with particularly low concentrations, it is also necessary to consider using a back-illuminated CCD to improve the sensitivity of the spectrometer. The back-illuminated CCD makes the back of the CCD as thin as 10-15 µm by flipping the CCD, and the incident photons enter the CCD from the back, so that polysilicon will not appear in the light incident path. In this way, a quantum efficiency of over 90% can be obtained (the corresponding front-illuminated CCD has a quantum efficiency of only about 35% in this band).

Raman spectroscopy has very good fingerprint spectral characteristics, and there may be some relatively close Raman spectral characteristic peaks. Some specific applications may require the spectrometer to have a higher resolution to distinguish two Raman peaks that are very close together. The most common Raman configuration uses 532nm or 785nm lasers, Bidatech can provide low wavenumbers to 65cm-1, high wavenumbers up to 3300cm-1 (785nm) or 4200cm-1 (532nm), and its spectral resolution can reach the highest around 3-4.5cm-1.