Spectrometers Double monochromators

In Raman measurements [57], the 514-nm line of an Ar+ laser, the 325-nm line of a He-Cd laser, and the 244-nm line of an intracavity frequency-doubled Ar+ laser were employed. The incident laser beam was directed onto the sample surface under the back-scattering geometry, and the samples were kept at room temperature. In the 514-nm excitation, the scattered light was collected and dispersed in a SPEX 1403 double monochromator and detected with a photomultiplier. The laser output power was 300 mW. In the 325- and 244-nm excitations, the scattered light was collected with fused silica optics and was analyzed with a UV-enhanced CCD camera, using a Renishaw micro-Raman system 1000 spectrometer modified for use at 325 and 244 nm, respectively. A laser output of 10 mW was used, which resulted in an incident power at the sample of approximately 1.5 mW. The spectral resolution was approximately 2 cm k That no photoalteration of the samples occurred during the UV laser irradiation was ensured by confirming that the visible Raman spectra were unaltered after the UV Raman measurements. 

High-quality spectrometers could have two monochromators in series (called a double monochromator) to reduce stray light. Unwanted radiation that passes through the first monochromator is rejected by the second monochromator. 

Additional help is to be gained by eliminating spectrometer "stray light . This is normally achieved by using double monochromators" in the more sophisticated spectrometers (by Spbx, Cary, Coderg and Jarbia-Ash). 

Luminescence. Both excitation and emission spectra were recorded using a Spex Fluorolog 202 B double monochromator fluorescence spectrometer. The spectrometer was operated in the front face mode with bandpass slits of 1.0 nm. 

Raman spectra of powdered samples in capillary tubes were obtained using a double monochromator spectrometer (Model 1401—Spex Industries, Inc.) with the blue laser line excitation (488 nm). The scattered radiation from the sample was taken at 90° to the incident beam. 

However, any spectrometer that uses CS and a double monochromator with an echelle grating makes it possible to reach any line within an extremely short period of time of much less than 1 s, as both the grating and the prism are stepper-motor controlled. This feature allows a fast sequential multi-element determination to be performed with the great advantage that flame conditions and burner... 

Figure 3.5-1 Types of Raman spectrometers a scanning spectrometer with triple additive monochromators, S source, D detector b instrument with subtractive double monochromator combined with polychromator and array detector AD c Rayleigh filter RF with polychromator and array detector.

Raman spectra were obtained using a Spex lAOl double monochromator and a detection system which utilized photon counting, in combination with a 6A7.1 nm laser exciting line from a krypton laser. The Spectrometer was coupled to an on-line computer which allowed the data to be collected, stored, corrected for phototube sensitivity, normalized and plotted. Powdered samples were loaded into 1 mm o.d. quartz X-ray capillaries in the Drilab, sealed temporarily with a plug of Kel-F grease, and the tube drawn down in a small flame outside the drybox. 

A Spectra-Physics Model 125 He-Ne laser was used in conjunction with a Spex Model 1400 Double Monochromator, in the spectrometer described by Miller, Rousseau, and Leroi, An ITT FW-130 Star-Tracker photomultiplier was used for detection. 

Raman Spectra. Microcrystalline samples of [XeFj JjPdFj ", [XCjFi/ljPdF, ", XCjFi/AuF,", and XeFj AuFj", enclosed in 1-mm o.d. quartz capillaries, were excited at 6328 A, using a 100-mW He-Ne ion laser, and spectra were recorded from a Spex Model 1400 double monochromator. Spectra were also obtained on a Cary S3 spectrometer equipped with a 100-mW At ion (4880-A) laser. The spectra are tabulated in Table IV and the AuF salt spectra are given in Figure 6. ... 

Raman Spectra.—The microcrystalline solids and a sample of liquid S2O6F2 were each contained in sealed thin walled 1-mm diameter Pyrex glass capillaries for Raman spectroscopy. The spectrometer employed a Spectra-Physics Model 125 He-Ne laser in conjunction with a Spex Model 1400 double monochromator. 

Jobin-Yvon Ramanor HG-2S spectrometer with double monochromator. Red light of 647 nm from a krypton-ion laser (Spectra Physics Model 165) and 514.5. 488 and 457.9 nm radiation from an argon-ion laser (Coherent Radiation Co., Model CR-2) were used. 

Figure 1.6. Spectra of solid glassy carbon obtained with a state-of-the-art spectrometer in 1985 (Spex 1403 double monochromator with photon counting PMT) and a multichannel/CCD spectrometer of 1996 (Chromex 250 spectrograph, back thinned silicon CCD) 514.5 nm laser at 50 mW in both cases measurement times and signal/noise ratios (SNR) as shown.

The convenhonal spectrometer consisted of a Coderg double monochromator equipped with a cooled PMT and was described in detail by Brooker et al. (1994). A 1 W laser was required to obtain spectra with adequate signal to noise ratio. A half-wave plate controlled the polarization of the incident beam. The 90° scattered light was analyzed with Polaroid films with accepted parallel or perpendicular polarized light. A quarter wave-plate in front of the entrance slit served to compensate for grating polarization preference. 

Figure 10.7 Schematic diagram of spectrometers and analysers in the infrared, (a) Single beam analyser containing a fixed monochromator or a filter used when a measurement at a single wavelength will suffice (b) dispersive spectrometer, double beam system. In contrast to spectrophotometers in the UV/Vis, the sample, located prior to the monochromator is permanently exposed to the full radiation of the source, knowing that the energy of the photons in this region is insufficient to break the chemical bonds and to degrade the sample (c) Fourier transform single beam model.

Such double beam instruments can be controlled more easily in processes by relays or microprocessors. No mechanics for automatic exchange of sample and reference cells have to be included. The energetic efficiency of the light paths is lower. A double monochromator supplies higher quality photometry. The spectral resolution can be increased and the amount of stray light is drastically decreased. The slit in-between the two monochromator parts is essential. A high performance instrument is shown in Fig. 4.3. Such spectrometers are rather expensive but are very useful in the examination of complex photoreactions as well as in the measurement of problematic samples such as turbid solutions, viscous samples, or thin films. 

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. 

Stray light can be reduced and higher resolution obtained by using double monochromators. An echelle spectrometer equipped with a predisperser has been used. As the two instruments are operated in tandem, the exit slit of the predisperser is the entrance slit of the monochromator. 

Fig. 4.6 Block diagram of a conventional multichannel Raman spectrometer. S, sample. Note, the double monochromator is operating in subtractive mode.

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