Domain spectral

Joo, C. de Boer, J. F., Spectral domain optical coherence reflectometric sensor for highly sensitive molecular detection, Opt. Lett. 2007, 32, 2426 2428... 

All methods mentioned in Table 1 operate (typically) in the frequency domain a monochromatic optical wave is usually considered. Two basically different groups of modeling methods are currently used methods operating in the time domain, and those operating in the spectral domain. The transition between these two domains is generally mediated by the Fourier transform. The time-domain methods became very popular within last years because of their inherent simplicity and generality and due to vast increase in both the processor speed and the memory size of modem computers. The same computer code can be often used to solve many problems with rather... 

Photoluminescence involves three types of information (i) emission versus wavelength (spectral-domain), (ii) intensity across a specific wavelength bandwidth (intensity-domain) and (iii) emission decay over time (time-domain or lifetime) where each fluorophore has a unique lifetime. Photoluminesence detection modes in general are classed as either steady state or time-domain where the former involves either spectral- or intensity-domain detection modes. 

It is important to realize that dispersion compensation can eliminate the high-order phase distortions (in the spectral domain) introduced by the objective lens, as discnssed above, but it cannot eliminate the scattering (in the spatial domain) that occnrs in depth imaging. Here we explore the nse of laser pulses that are dispersion compensated only before the medinm. In principle, it is possible to compensate for dispersion at greater depths, bnt if the dispersion of tissues is similar to that of pure water, it should be insignificant. Finally, we could titrate the amount of laser power nsed, increasing the intensity as the focal plane moves deeper into the tissue. 

In this chapter we explore several aspects of interferometric nonlinear microscopy. Our discussion is limited to methods that employ narrowband laser excitation i.e., interferences in the spectral domain are beyond the scope of this chapter. Phase-controlled spectral interferometry has been used extensively in broadband CARS microspectroscopy (Cui et al. 2006 Dudovich et al. 2002 Kee et al. 2006 Lim et al. 2005 Marks and Boppart 2004 Oron et al. 2003 Vacano et al. 2006), in addition to several applications in SHG (Tang et al. 2006) and two-photon excited fluorescence microscopy (Ando et al. 2002 Chuntonov et al. 2008 Dudovich et al. 2001 Tang et al. 2006). Here, we focus on interferences in the temporal and spatial domains for the purpose of generating new contrast mechanisms in the nonlinear imaging microscope. Special emphasis is given to the CARS technique, because it is sensitive to the phase response of the sample caused by the presence of spectroscopic resonances. 

Refs [19, 20, 29], One can examine the universal dynamical decoherence and disentanglement formalism from two complementary perspectives, namely, the time and spectral domains. 

In the spectral domain, one can express the same decoherence rate as in Eq. (4.202) by the following equation ... 

Finally, cross-decoherence can be understood from the spectral-domain analysis as the coupling of two systems via common bath modes, that is, Eq. (4.203) is the overlap of three functions, namely, cross-coupling spectrum and the individual modulation spectra of the two systems. For example, if two systems couple to different modes, then in the absence of modulations, they will not experience any cross-decoherence. Hence, in order to impose cross-decoherence, one should modulate the systems in such a way that they effectively couple to the same modes with the same strength. On the other hand, if one wishes to eliminate cross-decoherence, one should apply local modulations, such that the modulation spectra have different peaks, which would result in the two systems coupling to different modes and thus experiencing no cross-decoherence. 

Absorbance measurements for solutions are carried out in cells with a small optical path d to minimise absorption of the solvents, none of which are transparent in this spectral domain. Uncertainty in the value of d is related to the fragility of the material used for the cell windows and their construction. Therefore, it is necessary to periodically calibrate the optical path. 

These instruments allow a spectrum to be obtained which is a plot of absorbance (cf. 11.11) as a function of wavelength (Fig. 11.1). Wavelengths are expressed in nanometres (nm), the recommended unit in this spectral domain. 

A compound that is transparent within a spectral domain when in its isolated state can sometimes absorb when in the presence of a species with which it can interact through a donor-acceptor relationship (D-A). This phenomenon is related to the passage of an electron from a bonding orbital of the donor (which becomes a radical cation) to an unoccupied orbital of the acceptor (which becomes a radical anion), which has a close energy level (Fig. 11.6). The position of the absorption band in the spectrum is a function of the ionisation potential of the donor and the electron affinity of the acceptor. The value of e for these transitions is usually large. 

Two light sources are commonly used in this spectral domain. An incandescent lamp made from a tungsten filament housed in a glass envelope is used for the Visible... 

The spectral domain of the UV/Visible is well known because it includes the visible part of the spectrum and is widely used in quantitative analysis. Measurements are based on the Beer-Lambert law, which relates the absorption of light under certain conditions to the concentration of a compound. 

It is not necessary that the compound contain a chromophore as long as derivatisation is carried out before measurement to ensure absorption of the light. Through derivatisation, it becomes possible to quantify a chemical species that has no significant absorption because it is weak or, alternatively, because it lies in the same spectral domain as interferences. 

The term colorimetry comes from the fact that initial measurements in this spectral domain, well before the invention of spectrophotometers, were carried out with white light without any optical instrument. Visual comparison of the sample colour with that of a reference solution of known concentration was then performed. 

The instrument uses three recordings stored in memory a spectrum of the sample (composed of the two compounds to be analysed) and a spectrum of each of the pure components in the same spectral domain (reference solutions of known concentrations). 

Spectrophotometers were improved somewhat by dual-wavelength detectors, but it was not until the development of the photodiode array (PDA) that spectrophotometric techniques were revolutionized. The photodiode array detector, which can acquire data in both the time and spectral domains, has led to considerable improvements in HPLC food analysis for the purpose of identifi-... 

A variant on spectral subtraction is the INTEL technique [Weiss et al., 1975], in which the square root of the magnitude spectrum is computed and the rooted spectrum is then further transformed via a second FFT. Processing similar to that described above is then performed in this pseudo-cepstral domain. The estimate of the speech amplitude function in this domain is transformed back to the magnitude spectral domain and squared to remove the effect of rooting the spectrum. 

In principle, with the scattering wavefunctions at one s disposal, it is possible to segment a complex superposition of single-ionization states in to portions belonging to different symmetries, channels, and spectral domains. Indeed,... 

Figure 1.2 Interferogram recorded by a d.c.-coupled detector in which the signal counts can vary from 0 to 16384 (top). Fourier transformation of the recorded interferogram profile yields a single-beam spectrum (middle). Single-beam spectra from a sample can be ratioed point-by-point in the spectral domain to single-beam spectra acquired without a sample in the beam path, yielding absorbance spectra (bottom). The absorbance features in a spectrum can be correlated to the molecular properties of the sample (dark profile), while a featureless spectrum (light profile) denotes the lack of sample in the beam path.

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