Optical Slits

A system of slits (Fig. 2.17) is used to select radiation from the light beam both before and after it has been dispersed by the wavelength selector. The jaws of the slit are made of metal and are usually shaped like two knife edges. They can be moved relative to each other to change the mechanical width of the sht as desired. For the sake of simplicity, Fig. 2.17 does not show the system of lenses or mirrors used in a monochromator to focus and colhmate the light as needed. 

The physical distance between the jaws of the slit is called the mechanical slit width. Instruments normally have a micrometer scale attached so that one can read off the 

If the mechanical slit width were made wider, the spectral bandpass would simultaneously increase and vice versa. The spectral bandpass is one of the components of the spectrometer that affects resolution. For example, with the mechanical slit settings described, it would not be possible to resolve an emission line at 229.0 nm from the 

8 nm Cd line, because both would pass through the slits. In practice, the slits are kept as narrow as possible to ensure optimum resolution however, they must be wide enough to admit sufficient light to be measured by the detector. The final choice of slit width is determined by the analyst based on the particular sample at hand. A good rule of thumb is to keep the slits as narrow as possible without impairing the functioning of the detector or the ability to detect a specified amount of analyte. 

There are a number of different types of photon detectors, including the photomultiplier tube, the silicon photodiode, the photovoltaic cell, and a class of multichannel detectors called charge transfer devices. Charge transfer detectors include photodiode arrays, charge-coupled devices (CCDs), and charge-injection devices (ClDs). These detectors are used in the UV/VIS and IR regions for both atomic and molecular spectroscopy. 

The entrance slit permits passage of a beam of light from the source. Radiation from the light source is focused on the entrance slit. Stray radiation is excluded. After being passed through the entrance slit, the radiation is collimated into a parallel beam of light, which falls onto and 

The physical distance between the jaws of the slit is called the mechanical slit width. Instruments used to have a micrometer scale attached so that one read off the mechanical slit width directly modern computer-controlled instruments set and read the slit width through the software that controls a stepper motor operating the slit mechanism. In UV absorption spectroscopy, mechanical slit widths are of the order of 0.3-4 pm. In IR spectroscopy, slit widths between 0.1 and 2.0 mm are common for dispersive instruments. There are no slits in FTIR spectrometers. 

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As the temperature dependence of the CTL spectrum has information about the type of vapor, the present authors and coworkers [17] reported a method to recognize organic vapors by means of spectrum-temperature imaging. For this purpose, a system to simultaneously measure the CTL spectra at various temperatures was developed (Fig. 27). The sintered layer of the CTL catalyst is laid on a ceramic heater substrate of 5 x 60 mm2, which has a temperature distribution ranging from 440 to 530 °C along the stream of a sample gas in a quartz tube. A mask with an optical slit of 0.3 mm width is placed on a quartz tube. The CTL emission passing through the slit is focused on... 

Nishimoto, T., Fujiyama, Y., Abe, H., Kanai, M., Nakanishi, H., Arai, A., Micro-fabricated CE chips with optical slit for UV absorption detection. Micro Total Analysis Systems, Proceedings of the 4th TTAS Symposium, Enschede, Netherlands, May 14-18, 2000, 395-398. 

Milliseconds-to-microseconds This time domain is covered with either gated image devices or with the rotating optical slit, a recent EG G—PARC development,(12). The intensified OIDs, e.g., SIT and ISIT, have a triode-structured image section... 

Figure 9. The experimental setup for studies of transient optical phenomena using a rotating optical slit...

Figure 10. The simultaneous acquisition of the entire spectral record of a transient optical phenomenon, using the rotating optical slit in conjunction with the SIT detector operated in the 2D mode.

Figure 3.20. Schematic diagram of the Derivatograph. I. crucible for the sample 2. crucible for the inert material 3. porcelain tube 4. thermocouples 5. electric furnace 6. torsionless lead 7, balance 8. coil 9. magnet lO. DTG-galvanometer 11. T-galvanometer 12. DTA-galvanometer 13, lamps 14, optical slit 15, photorecording cylinder 16. photographic chart.

Figure 8.4l. Apparatus for the parallel recording of DTA. T, TG. DTG. TGT- and DTGT curves (86). 1. compressed test piece 2. compressed reference substance 2. furnace 4. silica bell 5, inlet tube for carrier gas 6. tube for eas extraction 7. silica tube S. suka tube with stirrup-shaped end 9. thermoelement 10. diaphragms 11. light cell 12- lamps l3. optical slit 14. magnet l5. coil 16. galvanometer 17. photographic paper 18. damns transformer 19, absorber 20. electrodes 2l, amplifier 22. vacuum pump 23. automatic burette 24. potentiometer 25. servomotor.

Figure 2.29 A grating monochromator showing the optical slits. The entrance slit is on the right and the exit slit on the left. (From Dean, J.A. and Rains, T.C., eds.. Flame Emission and Absorption Spectrometry, Vol. 2, Marcel Dekker, Inc., New York, 1971. Used with permission.)...

Shaft speed and torque, measured by a shaft mounted optical slitted disc system, providing filtered analogue voltage outputs. 

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