Background suppression

Plenary 10. Hiro-o Hamaguchi, e-mail address lilrama ,chem.s.u-tokvo.ac.ip (time and polarization resolved multiplex 2D-CARS). Two-dimensional (tune and frequency) CARS using broadband dye source and streak camera timing. Studies dynamic behaviour of excited (pumped) electronic states. Follows energy flow within excited molecules. Polarization control of phase of signal (NR background suppression). 

Lagutchev A, Hambir SA, Dlott DD. 2007. Nonresonant background suppression in broadband vibrational sum-frequency generation spectroscopy. J Phys Chem C 111 ... 

A significant development in the FRET imaging field has been the systematic implementation of spectral resolution [15-20], including D-A population analysis [8, 19] (see also Chapter 8), often in the context of single-molecule determinations [21-26] see focus issue on this subject, Nature Methods, June 2008. Invariably, photobleaching phenomena [21, 27, 28] intervene either as a hindrance (that can be minimized, CLEM [29]) or a facilitation of the FRET determination [1, 30], The equally important issue of background suppression or compensation can be achieved by novel means photon-free (bio)chemical instead of photonic excitation... 

We first review the essentials of the phase distribution of the electric fields at the focus of a high numerical aperture lens in Section II. After discussing the phase properties of the emitted signal, in Section HI we zoom in on how the information carried by the emitted held can be detected with phase-sensitive detection methods. Interferometric CARS imaging is presented as a useful technique for background suppression and signal enhancement. In Section IV, the principles of spatial interferometry in coherent microscopy are laid out and applications are discussed. The influence of phase distortions in turbid samples on phase-sensitive nonlinear microscopy is considered in Section V. Finally, in Section VI, we conclude this chapter with a brief discussion on the utility of phase-sensitive approaches to coherent microscopy. 

Marowsky, G., and Liipke, G. 1990. CARS-background suppression by phase-controlled nonlinear interferometry. Appl. Phys. B 51 49-51. 

Ion chromatography (IC) offers the analytical tool for the determination of each of the inorganic acids in a single sample. The principle of ion chromatography is the separation and measurement of ions in solution using ion exchange resins, background suppression, and conductimetric detection (5). 

In condensed-phase CARS, the effects of the nonresonant susceptibility x(3)nr are most profound when a sample with weak Raman modes is embedded in a nonlinear medium. The nonresonant background of the latter can be easily comparable to or larger than the resonant contribution from the sample of interest. This is a situation commonly encountered in biological applications of CARS microscopy. Depending on the experimental situation, the CARS detection sensitivity to weak resonances can then be restricted either by the nonresonant background or by the photon shot-noise [62]. To maximize either the relative or the absolute CARS intensity, nonresonant background suppression schemes [44, 60, 61, 63, 64] and optical heterodyne detection (OHD) techniques [65-67] have been developed during recent years. 

In conclusion, although the increased propensity for photodamage by femtosecond pulses and the requirement for an additional delayed laser pulse can be disadvantageous, time-resolved CARS microspectroscopy not only provides a means for efficient and complete nonresonant background suppression but also offers the prospect for monitoring ultrafast processes of molecular species inside a sub-femtoliter sample volume [64, 152-154]. 

CARS-CS experiments have been reported in the low-concentration limit ((N) <<1) on freely diffusing submicron-sized polymer spheres of different chemical compositions using both the E-CARS [162, 163] and the polarization-resolved CARS [163] detection scheme for efficient nonresonant background suppression. These experiments have unambiguously demonstrated the vibrational selectivity of CARS-CS, the dependence of its ACF amplitude on the particle concentration, (N), the dependence of lateral diffusion time, Tp, on the sphere size, and the influence of the microviscosity on its Brownian motion. 

The results using CCDs for the direct measurement of X-rays from pH [22] were consistent with the values obtained from the earlier experiments mentioned above. The superior background-suppression capabilities of the pixel devices led to an improvement of the peak-to-background ratio (Fig. 3). The new world-average values for the strong-interaction effects are listed in Table 3 together with typical results from model calculations. 

Since the fast centrifuge system SISAK is equipped with liquid scintillation counting LSC [12,58], it is in principle capable of investigating short-lived a-decaying nuclides of the transactinides, p/y pulses and a pulses are distinguished by pulse-shape discrimination PSD and pile-up pulses are rejected by a pile-up rejection system PUR. This analog electronics proved to result in insufficient background suppression. Thus, two new approaches... 

In this section we present theoretical and experimental demonstrations of a vibrational spectroscopic technique, vibrational echo spectroscopy (VES) (54,55). The VES technique can generate a vibrational transition spectrum with background suppression using the nonlinear vibrational echo pulse sequence. In contrast to the previous results, VES is a utilization of vibrational echoes to measure spectra rather than dynamics. In a standard vibrational echo experiment, the wavelength of the IR light is fixed, and the delay, r, between the excitation pulses is scanned. In VES, r is fixed and the wavelength is scanned. 

Background suppression in VES is in some respects analogous to NMR background suppression techniques (56,57). In both types of spectroscopy, coherent pulses sequences are used to remove unwanted spectral features. 

IV) Residual background suppression. The residual background has been evaluated with two different methods the Alpha fit and the Ring method. 1) Alpha method the distribution of the Alpha parameter has been fitted with a second order polynomial, without the linear term, between 20 and 80 0 (where only background is present). Then the fit extrapolation to the 0-12.5° region... 

Pacholski C, Sailor MJ (2007) Sensing with porous silicon double layers a general approach for background suppression. Phys Stat Sol C 4 2088-2092... 

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