Wavelength modulation spectroscopy

Bruno Batz, Thermal and Wavelength Modulation Spectroscopy... 

B. O. Seraphin, Electroreflectance R L. Aggarwal, Modulated Interband Magnetooptics D. F. Blossey and Paul Handler, Electroabsorption B. Batz, Thermal and Wavelength Modulation Spectroscopy 7. Balslev, Piezopptical Effects... 

The strength of wavelength modulation spectroscopy is its relative simplicity, its main disadvantage being its sensitivity to all absorbing species in the optical path and to any fairly rapid wavelength dependence of the monochromator output or detector response. 

In summary, the three advantages of IRES over wavelength modulation photometric spectroscopy are ... 

Presently, grating monochromators are used every time a sample must be illuminated with quasi-monochromatic radiations that are tunable in a broad spectral range or for experiments in the visible-UV range. Another interest of dispersive monochromators is the possibility of wavelength modulation of the output of these monochromators in order to get the first derivative of the transmission spectrum. This has the advantage of increasing the sensitivity, and this technique is also used in laser spectroscopy. 

There are two regimes of FM spectroscopy, the first is when the modulation frequency is greater than the line width of the absorption feature, and the second is when it is less. It is in the latter regime that the Brookhaven group performs their experiments, which is sometimes called wavelength modulation. The Brookhaven group scans an absorption profile by changing the carrier frequency. The output, /(coc), has both absorption and dispersion elements that depend on amplitude or phase modification, respectively, as is shown in Eq. 10,... 

Wavelength modulation spectroscopy involves modulating the laser current at a frequency, /, fypically... 

Synchroton radiation has been employed as a spectral source for a study of the absorption of HCN and DCN in the wavelength range 80—120nm. A vacuum-u.v. spectrophotometer for absorptions in the region 105—200 nm has been described. Solid-, liquid-, and gas-phase samples could be analysed at temperatures from —200 to 100 °C and at pressures between 0 and 150 atmospheres. The absorption spectrum of tra j-di-imide in the vacuum-u.v. has been measured. First-derivative u.v. spectroscopy has been employed in the analysis of Watts nickel plating solutions for trace amounts of saccharin. Impurity levels of 0.1 p.p.m. have been recorded. A wavelength modulated derivative spectrophotometer with a multi-pass absorption cell has been developed for the automatic analysis of atmospheric pollutants. Traces of SOj, NO, and NO2 were detected with limits of 15, 13, and Sp.p.b., respectively. A double-beam single-detector absorption spectrometer has been constructed. Independence... 

Fig. 1.61 Section of CS2-overtone spectrum. Comparison of optoacoustic detection (a) and absorption spectroscopy with wavelength modulation (b) (G.H. Wenz, Thesis, K.L.)...

F.S. Pavone, M. Inguscio, Frequency- and wavelength-modulation spectroscopy Comparison of experimental methods, using an AlGaAs diode laser. Appl. Phys. B 56, 118 (1993)... 

Kim S, Scherson DA (1992) In situ UV-visible reflection absorption wavelength modulation spectroscopy of species irreversibly adsorbed on electrode surfaces. Anal Chem 64(24) 3091-3095... 

Fig. 10.21. Arrangements for frequency modulation spectroscopy with diode lasers. In (a) low frequencies are employed and the term wavelength modulation spectroscopy pertains. In (b) high frequencies are used and discrete components replace the lock-in amplifier [10.84]...

Oh, D. B. Paige, M. E. Bomse, D. S., Frequency Modulation Multiplexing for Simultaneous Detection of Multiple Gases By Use of Wavelength Modulation Spectroscopy With Diode Lasers , Appl. Opt. 1998, 37, 2499-2501. 

Dochow, S., Bergner, N., Matthaus, C., Praveen, B.B., Ashok, PC., Mazilu, M., Krafft, C., Dholakia, K., and Popp, J. (2012) Etaloning, fluorescence and ambient light suppression by wavelength modulated Raman spectroscopy. Biomed. Spectrosc. Imaging, 1, 383 -389. 

Praveen, B.B. et al. (2012) Fluorescence suppression using wavelength modulated Raman spectroscopy in fiber-probe-based tissue analysis. 

There have been a few other experimental set-ups developed for the IR characterization of surfaces. Photoacoustic (PAS), or, more generally, photothemial IR spectroscopy relies on temperature fluctuations caused by irradiating the sample with a modulated monocliromatic beam the acoustic pressure wave created in the gas layer adjacent to the solid by the adsorption of light is measured as a fiinction of photon wavelength... 

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