Czerny-Turner grating monochromator

Monochromators (a) Czerny-Turner grating monochromator, (b) Bunsen prism monochromator. 

Figure 9- 1.1b is a schematic of a typical double-beam-intime instrument. The beam from the hollow-cathode source is split by a mirrored chopper, one half passing through Ihe tlame and the other half around it. The two beams are then recombined by a half-silvered mirror and passed into a Czerny-Turner grating monochromator a photomultiplier tube serves as Ihe transducer. The output from the latter is the input to a lock-in amplifier that is synchronized with the chopper drive. The ratio between the reference and sample signal is then amplified and fed to the readout, which may be a digital meter or a computer. 

FIGURE 13. Schematic of the optics of a double monochromator. There are three slits marked SI, S2, S3 two plane gratings marked G1 and G2 four concave mirrors, Ml, M2, M5, M6 and two 45° mirrors, M3 and M4. The middle slit S2 connects the two Czerny-Turner grating monochromators and should be set slightly wider than SI and S2 to allow for different alignments in the two monochromators. 

M3, which compensates for aberrations and yields an excellent quality of image b) Czerny-Turner design, similar in conception, incorporating two spherical mirrors. M and jf/4 c) design with a concave grating (7( allowing simultaneous dispersion and focusing of the radiation. The spectral bandwidth of these monochromators depends on the width of the entrance and exit slits, F, and F2-... 

Figure 9.12 Monochromator gratings, (a) Ebert assembly incorporating a single concave spherical mirror M3. Able to compensate for aberrations this monochromator gives excellent image quality, (b) Of similar design to Ebert the Czerny-Turner assembly contains two spherical concave mirrors Mj and M4. (c) The concave grating in this design permits hoth dispersion and focussing of the radiation. The spectral bandwidth of these monochromators depends upon the width of the entrance and the exit Fj slits, respectively.

The spectrometers used are adapted either for sequential or simultaneous multi-element measurements. Commonly used grating spectrometers in plasma AES include (i) spectrometers with the Paschen-Runge mount, (ii) echelle spectrometers, (iii) spectrometers with Ebert and Czerny-Turner mounts, (iv) spectrometers with Seya-Namioka mounts, and (v) double monochromators. Also Fourier transform spectrometers may be used in plasma AES. 

Czerny-Turner monochromators Two mirrors are used to reflect and focus the polychromatic and diffracted beams. Wavelengths are selected by using a computer to rotate the grating in various ways. This design is shown in Figure 6. As the grating rotates, a different wavelength is focused onto the exit slit. 

A conventional monochromator (either Ebert, Czerny-Turner, Littrow or Echelle) may be used (see AAS sections for details), but some of the more basic instrumentation uses interference filters. These are optical filters that remove large bands of radiation in a nondispersive way. A dispersion element such as a prism or a grating is therefore not required. Only a relatively narrow band of radiation is allowed to pass to the detector. The disadvantage with such devices is that they are not particularly efficient and hence much of the fluoresced light is lost. An alternative development is the multi-reflectance filter. This is shown diagramatically in Figure 3, and has the... 

FIGURE 3 Schematic representation of the most frequently used grating-based monochromators (A, B, C) and polychromators (D, E, F). A and D are known as Czerny-Turner design. Fastie-Ebert (B) and Littrow (C) have similar designs in that both use a single reflective mirror. A Rowland circle polychromator is depicted in E, and F represents an Echelle spectrograph. 

Figure 5.11. A Czerny-Tumer monochromator. Light (A) is focused onto an entrance slit (B) and is collimated by a curved mirror (C). The colhmated beam is diffracted liom a rotatable grating (D) and the dispersed beam refocused by a second mirror (E) at the exit slit (F). Each wavelength of light is focused to a different position at the sht, and the wavelength that is transmitted through the sht (G) depends on the rotation angle of the grating.(http //upload.wikimedia.oig/wikipedia/commons/e/e8/ Czerny-turner.png)...

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