Spectrometers Raman grating

Raman grating spectrometer with single channel detector... 

There are many different Raman spectrometers in current use, almost all of which are suitable for this experiment. A general description of Raman instruments with grating monochromators and laser sources is given in Chapter XIX. Before beginning the experiment, you should review the pertinent material in Chapter XIX and read carefully any available information about the actual instrument to be used in the laboratory. Use the speetrometer with eare if in doubt, ask the instructor for advice about proper procedures. 

If possible, make more accurate measurements of the wavelengths using a high-resolution grating spectrometer as indicated in Fig. 2. The instructor will advise on the most appropriate measurement procedure for the particular setup employed. The spectrometer should have 0.1-nm resolution, or better if possible, and should be equipped with a photomultiplier or charge-coupled detector (CCD). An instrument used for Raman or fluorescence measurements would be quite suitable. 

Raman spectroscopy underwent almost the same change in instrumentation from prism to grating spectrometers. Flowever, interferometers were only seldom used (Jennings, Weber and Brault, 1986). 

According to this equation, the ratio between the length of the slit h and the focal length of the collimator / is relevant for the spectral optical conductance of a grating spectrometer. It is usually on the order of 0.01 values of up to 0.2 aie only reached in very special cases (the old model 81 Cary Raman spectrometer with an image sheer , made in 1960 ). 

The detector noise of a spectrometer operating in the visible range can be very low (as for a grating Raman spectrometer with a cooled photomultiplier). In this case, the main source of noise is the statistical noise of the analyzed radiation d>s, according to Poisson statistics — v - The signal-to-noise ratio, SNR, is therefore given by ... 

Conventional Raman spectroscopy employs nonabsorbing samples and grating spectrometers. The liquid sample is irradiated with the exciting radiation, usually a laser beam. In a direction perpendicular to the laser radiation, an image of this part of the sample is produced by the entrance optics, irradiating the grating with the Raman radiation through the entrance slit (Fig. 3.5-5 a). 

Figure 3.5-5 Sample arrangement for Raman spectroscopy. Optimal illumination of a a grating spectrometer in the 90° arrangement b of an interferometer in the 180° arrangement.

Raman spectra were obtained from scunples contained in quartz capillaries or tubes, or Teflon FEP tubes of in. diameter. For lower temperatures (to -lOO K) samples were held in a stream of cold nitrogen (jacketed by warm nitrogen to prevent ice formation). Spectra were recorded from a J-Y Ramanor HG25 Spectrometer with a double holographic grating monochromator, using either a krypton (647.1 nm) or an argon ion (514.5 or 488.0 nm) laser. 

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