Nonresonance spectrum response

Fig. 6.8. A Principle of frequency-multiplexed CARS microspectroscopy A narrow-bandwidth pump pulse determines the inherent spectral resolution, while a broad-bandwidth Stokes pulse allows simultaneous detection over a wide range of Raman shifts. The multiplex CARS spectra shown originate from a 70 mM solution of cholesterol in CCI4 (solid line) and the nonresonant background of coverglass (dashed line) at a Raman shift centered at 2900 cm-1. B Energy level diagram for a multiplex CARS process. C Schematic of the multiplex CARS microscope (P polarizer HWP/QWP half/quarter-wave plate BC dichroic beam combiner Obj objective lens F filter A analyzer FM flip mirror L lens D detector S sample). D Measured normalized CARS spectrum of the cholesterol solution. E Maximum entropy method (MEM) phase spectrum (solid line) retrieved from (D) and the error background phase (dashed line) determined by a polynomial fit to those spectral regions without vibrational resonances. F Retrieved Raman response (solid line) calculated from the spectra shown in (E), directly reproducing the independently measured spontaneous Raman response (dashed line) of the same cholesterol sample...

Derivative Detection of EPR Transition. The EPR spectrum is usually displayed as the first derivative of the absorption y"(H), because the nonresonant low-frequency and low-amplitude RF modulation (co1/ 2% = typically 100 kHz) applied to the coils near the magnet is detected by a rectifier in addition to the drop in microwave power level due to the RF resonant absorption (typically co0/27c = 9.1 GHz if H0 = 0.34T) The signal is processed by a phase-sensitive circuit, which detects a back-and-forth sweep across resonance in small magnetic field increments (relative to the DC field and to the width of the measured spectrum), thus generating a response df /dH (see Fig. 11.60). 

Just as for the lower-order responses, we have kept the imaginary terms in the denominators in order to maintain convergence of the second-order hyperpolarizability at all frequencies, as well as to indicate the possibility of including damping in the near-resonant and resonant regions of the frequency spectrum. In the nonresonant region, however, the imaginary terms may be left out, and the expression for Wi, 0)2, cuj) can be written more compactly as... 

Spectroscopic observables can be categorized in several ways. We can follow a temporal profile or a frequency resolved spectrum we may distinguish between observables that reflect linear or nonlinear response to the probe beam we can study different energy domains and different timescales and we can look at resonant and nonresonant response. This chapter discusses some concepts, issues, and methodologies that pertain to the effect of a condensed phase environment on these observables. For an in-depth look at these issues the reader may consult many texts that focus on particular spectroscopies. ... 

Mechanism (a) responsible for libration band near the edge of far IR spectrum and for nonresonance Debye relaxation spectrum... 

The spectrum (Figure 19c) required only a short Raman collection, because shear-force controlled apertureless internal reflection Raman SNOM also creates the characteristic enhancement of the Raman reflection back to the sharp tapered fiber. Further, resonant Raman SNOM spectra of silicon (519.7 cm ) under an old (5 nm) or a freshly grown silica layer, and nomesonant Raman SNOM of these layers (500 cm ) as well as of gallium nitride (nonresonant El (TO) and E2 Raman modes at 560.8 and 570.4 cm ) on alumina (subtraction of the Raman response of support and fiber) with the shear-force apertureless technique (using 488 nm light) at total collection times of <10 min have been reported in Ref. 25. 

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