Spectrometers monochromator

X-ray absorption near edge stmcture (XANES) investigations were made at the Russian-German beamline of BESSY synchrotron radiation facility. Energy resolution was of 0.03 eV. Ultrasoft X-ray emission spectra (USXES) were obtained with X-ray laboratory spectrometer-monochromator RSM-500 with the energy resolution of 0.3 eV in die range of P L2,3-spectra. The depth of analysis in both cases was about 10-20 nm. 

The angular and spectral dependences of X-ray reflectivity were studied with DRON-3 X-ray diffractometer (X = 0.154 nm) and X-ray reflectometer designed in IPM RAS on the basis of a RSM-500 spectrometer-monochromator (4-50 nm wavelengths). 

The first requirement is a source of infrared radiation that emits all frequencies of the spectral range being studied. This polychromatic beam is analyzed by a monochromator, formerly a system of prisms, today diffraction gratings. The movement of the monochromator causes the spectrum from the source to scan across an exit slit onto the detector. This kind of spectrometer in which the range of wavelengths is swept as a function of time and monochromator movement is called the dispersive type. 

Due to the rather stringent requirements placed on the monochromator, a double or triple monocln-omator is typically employed. Because the vibrational frequencies are only several hundred to several thousand cm and the linewidths are only tens of cm it is necessary to use a monochromator with reasonably high resolution. In addition to linewidth issues, it is necessary to suppress the very intense Rayleigh scattering. If a high resolution spectrum is not needed, however, then it is possible to use narrow-band interference filters to block the excitation line, and a low resolution monocln-omator to collect the spectrum. In fact, this is the approach taken with Fourier transfonn Raman spectrometers. 

Figure 1 Drawing of single-channei Raman spectrometer showing Czerny-Turner type doubie monochromator. Coiiecting optica for scattered beam are not shown.

A simple spectrometer that we have used successfully is shown in Figure 2. Electrons from an electron microscope hairpin tungsten filament are focused with an Einzel lens onto the monochromator entrance slit, pass through the monochromator and exit slit, and are focused on the sample s surface by additional electrostatic... 

Three different types of grating spectrometer detection sterns are used (Figure 3) sequential (slew-scan) monochromators, simultaneous direct-reading polychroma-... 

Figura 3 Grating spectrometers commonly used for ICP-OES (a) monochromator, in which wavelength is scanned by rotating the grating while using a singie photomultiplier tube (PMT) detector (b) polychromator, in which each photomultiplier observes emission from a different wavelength (40 or more exit slits and PMTs can be arranged along the focal plane) and (c) spectrally segmented diode-array spectrometer.

Some X-ray photoelectron spectrometers are equipped with monochromators that can be used to remove unwanted radiation, such as the continuous radiation and even some of the weaker characteristic X-rays such as K<,3, K 4, Kas, and Ko,6, from the emission spectrum of the anode. A monochromator can also be used to resolve the K i,2 line into its two components K i and Ka2- Using a monochromator has at least two beneficial effects. It enables the narrow, intense K<, line to be used to excite spectra at very high resolution. A monochromator also prevents unnecessary radiation (continuous, K<,2, Ka3, K<,4, Kas, and Ka6) that might contribute to thermal or photochemical degradation from impinging on the sample. 

Today s commercially available chromatogram spectrometers usually employ diffraction gratings for monochromation. These possess the following advantages over prism monochromators which are still employed in the Schoeffel doublebeam spectrodensitometer SD 3000 and in the Zeiss chromatogram spectrometer ... 

When recording excitation and fluorescence spectra it must be ensured that monochromatic light falls on the detector This can best be verified in instruments built up on the kit principle or in those equipped with two monochromators (spectrofluonmeters) The majority of scanners commercially available at the moment do not allow of such an optical train, which was realized in the KM3 chromatogram spectrometer (Zeiss) So such units are not able to generate direct absorption or fluorescence spectra for the charactenzation of fluorescent components... 

A modern laser Raman spectrometer consists of four fundamental components a laser source, an optical system for focusing the laser beam on to the sample and for directing the Raman scattered light to the monochromator entrance slit, a double or triple monochromator to disperse the scattered light, and a photoelectric detection system to measure the intensity of the light passing through the monochromator exit slit (Fig. 7). 

Procedures for calibrating both monochromators in a fluorescence spectrometer using narrow line sources have been discussed (IS,18) care must be taken with placement of the calibration source. 

Atomic absorption spectrometers with dual monochromators are commercially available from Jarrell-Ash Division of Fisher Scientific Co.9 and from Instrumentation Laboratories Inc. 

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