Slits, of monochromator

Figure 7. Schematic diagram of photoionization mass spectrometer. Axis of quadrupole mass spectrometer is parallel to exit slit of monochromator mass spectrometer has been rotated 90° for purposes of illustration here.80...

FIGURE 18-9 Raman spectrometer with fiber-optic probe. In (a) a microscope objective focuses the laser radiation onto excitation fibers that transport the beam to the sample. The Raman scattering is collected by emission fibers and carried to the entrance slit of a monochromator or to the entrance of an interferometer. A radiation transducer, such as a photomultiplier tube, converts the scattered light Intensity to a proportional current or pulse rate (b) end view of the probe (c) end view of collection libers at entrance slit of monochromator. The colored circles represent the input fiber and the uncoiored circles the collection fibers. (Adapted from R. L. McCreery. 

Figure 24, Entrance slit of monochromator with image of hollow cathode source superimposed on it.

A detachable monochromator (19) developed by Spex Industries, was another approach in minimizing stray light. It is a modified Czerny-Turner spectrograph which can be coupled to the exit slit of a double monochromator and function as a variable bandpass, variable frequency filter. This accessory, while providing the versatility of a triple monochromator, does not add much mechanical and optical complexity and can be removed when not wanted. 

The fluorescence spectra of dilute solutions (A < 0.05) of the compound and the standard must be recorded under exactly the same experimental conditions (slits of the monochromators, high voltage of the photomultipliers, gain of the electronic devices). The temperature of the sample holder must be controlled because the... 

Figure 2. Experimental set-up for Raman spectroscopy. The desired laser line is isolated from other plasma lines by a narrow bandpass filter or broadband prism monochromator, then focused onto a sample in a capillary tube. A collecting lens placed at a 90° angle to the incident beam focuses the scattered light onto the entrance slit of a monochromator with output to a photomultiplier tube (in the case of a scanning instrument) or a diode array detector.

Figure 12.1 SGX-CAT beamline schematic. The components of the beamline include (1 (not shown), 8) photon shutters (2,4) beam transport tubes (3, 5) collimators and vacuum pumps (6) beam-defining slits (7) monochromator (9,10) focusing and harmonic rejection mirrors and (12) CCD detector, supporting base, and sample robot.

Atomic emission from the plasma is focused on to the entrance slit of the monochromator using a combination of convex or plano-convex lenses or a concave mirror. The combination of focusing optics, monochromator and detector is generally referred to as a spectrometer, although the heart of the device is the monochromator. A monochromator is an instrument that... 

Electrothermal atomizers are also suitable for AFS as, when an inert gas atmosphere is used, quenching will be minimized. In the nuclear, electronic, semiconductor and biomedical industries where detection limits have to be pushed as low as 1 part in lO (or 0.1 pg g- in the original sample), electrothermal atomization with a laser as excitation source (LIF-ETA) may be used. Figure 6.5 shows schematically a common way of observing the fluorescence in LIF-ETA. The fluorescence signal can be efficiently collected by the combination of a plane mirror, with a hole at its centre to allow excitation by the laser, positioned at 45° with respect to the longitudinal axis of the tube and a lens chosen to focus the central part of the tube into the entrance slit of the fluorescence monochromator. 

As the beam leaves the prism predisperser, it is focused on the entrance slit of the grating monochromator. The slit is curved, has variable width, and opens symmetrically about the chief ray (optical center line of system). The monochromator itself is of the off-axis Littrow variety (James and Sternberg, 1969 Stewart, 1970 Jennings, 1974) and uses a double-pass system described by McCubbin (1961). The double-pass aspect of the system doubles the optical retardation of the incident wave front and theoretically doubles the resolution of the instrument. The principal collimating mirror is a 5-m-focal-length, 102-cm-diam parabola. 

The simplest method of determining the function S, in the visible region of the spectrum is to take photomultiplier readings when the entrance slit of the monochromator is illuminated by a tungsten lamp giving light of known spectral distribution. If RSL represents the values so obtained, the spectral sensitivity is then calculated from... 

Fig. 8. Cross section of the cylindrical condenser for measurements of the kinetic energies of the photoelectrons from gas molecules. 1—fluorescent layer for intensity measurements of the incident light 2—thick metallic cylinder with wrought semi-annular slits 3—Teflon insulator 4—cylindrical grid 5—electron collector 6—LiF window 7—diaphragm 8—shutter 9—exit slit of the vacuum monochromator.

For recording of the emission spectrum, the emitted radiation is focussed on the slit of a monochromator and intensities measured attach wavelength. Since sensitivities of photocells or photomultipliers are wavelength dependent, a standardization of the detector-monochromator combination is necessary for obtaining true emission spectrum This can be done by using a standard lamp of known colour temperature whose emission characteristics is obtained from Planck s radiation law. The correction term is applied to the instrumental readings at each wavelength. Very often substances whose emission spectra have been accurately determined in the units of relative quanta per unit wavenumber intervals are... 

The light beam emitted by the source, which must be at the wavelength required for measurement, passes through the flame (or graphite furnace) in which the element is located in its atomic state. The beam is then focused on the entrance slit of the monochromator, located after the sample. The monochromator s role is to select a very narrow band of wavelengths. The optical path ends at the entrance slit of the photomultiplier tube. 

The linear dispersion. This is the spectral width in nm transmitted through the exit slit of the monochromator. It is given in units of nm/mm. For example 5 nm/mm would mean that the nominal bandwidth of the monochromatic light is 5 nm if the slit width is 1 mm. This defines the purity of the monochromatic light. 

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