Light grating dispersion

When a beam of high-intensity X-rays strikes a sample, the elements in the sample are excited and emit their own characteristic X-rays. The emitted rays are collimated on a crystal (which acts as a diffraction grating), and the light is dispersed in characteristic wavelengths. No preparation is required for the solid sample. Powder samples, solutions, or liquids can be placed in a sample cup wrapped with Mylar film that is transparent to X-rays. Like all X-ray analyses, this method is nondestructive and can be an automatic operation. 

In the TRPL measurements performed at 2K the excitation was made by a Ti sapphire laser system, with spectrally narrow (< 1 meV) 2 ps pulses. The emitted light was dispersed by a subtractive double-grating monochromator and detected with a multi-channel plate photomultiplier in the photon-counting mode with a time resolution of 20 ps. 

Fig. 1. Raman spectra of four waters, HjO, H2 0, D2O, and Di left) as ice at 77 K with a liquid N2 cell (see Fig. 6), 135° backscattering directly off the ice surface, laser power 250 mW, spectral slit width 6 cm and right) as neat liquid at room temperature with a capillary tube, 90° scattering, laser power 250 mW, spectral slit width 10 cm". Exciting radiation (488.0 nm) for all RR spectra was provided by a Coherent Innova 90-6 Ar ion laser. The scattered light was dispersed by a SPEX 1403 double monochromator equipped with 1800 grooves/mm holographic gratings and detected by a cooled Hamamatsu 928 photomultiplier tube under the control of a SPEX DM3000 data station as described elsewhere. ...

A collimated beam of light spectrally dispersed by a diffraction grating or a quartz prism yields a spectrum which can be used as a series of wavebands of near-monochromatic radiation. The intensities of different regions of the dispersed spectrum depend on the spectral distribution of the source. The dispersed spectrum is focused only on a few centimeters of the sample surface, and exposure is carried out for a constant duration. A microspectroscopic technique is generally used to study changes in absorbance properties of the sample subsequent to exposure. 

Incident light is focused on the sample cell. The transmitted radiation is refocused by means of lenses and collimated through the polychromator entrance slit, thus dispersed on the fixed holographic concave diffraction grating. Dispersed wavelengths are sampled on the photodiode array elements, positioned in the flat focal plane. The spectrum is obtained by electronic scanning through the sensitive receptor. 

Figure 2.27 An echelle spectrometer optical layout. The eohelle grating disperses the light to a second wavelength selector, called a cross disperser. The cross disperser may be a prism or a conventional grating. [ 1993-2014 PerkinElmer, Inc. All rights reserved. Printed with permission.

Fig. 12.4 A beam of light is dispersed by a diffraction grating into three component wavelengths X. andX,. In the configuration shown, only radiation with Xj passes through a narrow slit and reaches the detector. Rotating the diffraction grating in the direction shown by the double arrows allows other wavelengths to reach the detector.

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