Spectroscopy optical response functions

Linear and nonlinear infrared spectroscopy are powerful tools for probing the structure and vibrational dynamics of molecular systems." In order to take full advantage of them, however, accurate models and methods are required for simulating and interpreting spectra. A common approach for modeling spectra is based on computing optical response functions (ORFs)." Unfortunately, exact calculations of quantum-mechanical ORFs are not feasible for most systems of practical interest due to the large number of DOF. Instead, mixed quantum-classical methods ean provide suitable alternatives." " " ... 

Equation (4.2.11) describes the response to three delta pulses separated by ti =oi — 02 >0, t2 = 02 — 03 > 0, and t3 = 03 > 0. Writing the multi-pulse response as a function of the pulse separations is the custom in multi-dimensional Fourier NMR [Eml ]. Figure 4.2.3 illustrates the two time conventions used for the nonlinear impulse response and in multi-dimensional NMR spectroscopy for n = 3. Fourier transformation of 3 over the pulse separations r, produces the multi-dimensional correlation spectra of pulsed Fourier NMR. Foinier transformation over the time delays <7, produces the nonlinear transfer junctions known from system theory or the nonlinear susceptibilities of optical spectroscopy. The nonlinear susceptibilities and the multi-dimensional impulse-response functions can also be measured with multi-resonance CW excitation, and with stochastic excitation piul]. 

This is called the Kramers-Kronig (KK) relationship, from which the dielectric function e = ej + e2 can be derived [3.25]. Since e is also a linear response function, ej and 2 are again related by the KK relationship, thus the information contained in the dielectric function can be examined by concentrating on one of the two components of the dielectric function. We choose to work with 2(m) because it is what optical (X-ray) absorption spectroscopy measures and can be directly related to the atomic polarisability Im[a(o )] that appeared in (3.5). 

RESPONSE FUNCTION THEORY COMPUTATIONAL APPROACHES TO LINEAR AND NONLINEAR OPTICAL SPECTROSCOPY... 

Rizzo, A., Coriani, S., and Ruud, K. (2011) Response function theory computational approaches to linear and nonlinear optical spectroscopy, in Com-putational Strategies for Spectroscopy, From Small Molecules to Nano Systems, John Wiley Sons, Inc, pp. 77-135. 

The transparency, gloss and color of a film are important in many applications. The complete optical characterization of a polymer film would require measuring the optical response of the film as a function of wavelength, angles of incidence and detection (relative to the surface normal), film thickness and type of substrate. Despite the fact that a multitude of optical techniques are available for such measurements (UV-visible spectroscopy, ellipsometry, laser scattering and so forth), in most applications simple techniques using white light are employed [29]. 

Fig. 3.5. Experimental apparatus for time-resolved THz transmission spectroscopy. The sample is excited with a visible laser pulse delivered by delay line 3. A singlecycle THz electric-field transient probes the polarization response of the sample after time delay tv scanned by delay line 1. The transmitted THz amplitude is monitored via ultrabroadband electro-optic sampling in a THz receiver as a function of time T scanned by delay line 2. From [13]...

Ultrasound-based sensors for metal-coated fiber optic measurements based on interferometric determination of the displacement using a Michelson interferometer have also been designed. The input acoustic field can be detected by using two reference methods, namely (a) time-delay spectroscopy with a calibrated hydrophone (a hydrophone with known frequency response determining the sound pressure, the input displacement being obtained by simple algebra) and (b) the interferometric foil technique (the displacement of a metallized foil situated at the surface of the fluid measured by the interferometer used for fibre tip measurements). The frequency dependence of the transfer function compared well with the theoretical models [51]. 

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