Time-gated spectroscopy

The proof of concept of the two-photon antenna effect was established with Tb, Eu and Yb ions and two-photon time-gated spectroscopy has been evidenced. 

Yakovlev, V. V. 2007. Time-gated confocal Raman microscopy. Spectroscopy 22 34-41. 

Unusual behavior of the luminescence line at 417 nm has been detected by time-resolved spectroscopy. It is usually ascribed to Tb ", but sometimes in spectra with a narrow gate this line remains strong, while other lines of Tb disappear (Fig. 4.8b,c). The supposition that those lines are connected with Nd " " was confirmed by our study of CaW04 Nd, where, besides the known IR, the group of UV and violet lines with short decay times are detected, while in CaW04 Tb such lines are absent (Fig. 5.7). 

Figures 4.31a,b represent narrow luminescence hnes detected in barite by time-resolved spectroscopy. Much weaker lines at 446 and 672 nm accompany the strongest one at 588 nm. They have a relatively short decay time of 5 ps and emphasized in the spectrum with short gate. Such a combination of spectral and kinetic properties is not suitable for any trivalent REE besides P j2 f9/2...

Figure 7.36 Diagram of a single photon counting apparatus for time-resolved spectroscopy. L, pulsed light source S, sample P, photodiode F, filter or monochromator D, photomultiplier R, voltage ramp driver G, gate Cj, C comparators M, multichannel analyser...

This section will outline the developments of deep Raman spectroscopy from the use of time gating to spatially offset Raman spectroscopy to transmission Raman a sequence of increasing practical probing depth as advances have been made. This is counterbalanced by a reduction in depth selectivity with each new technique. An exploration of the potential use of deep Raman for breast cancer diagnostics will be used to illustrate the potential here. 

In order to actually carry out time resolved spectroscopy, the gating process must be synchronized to both the experiment and the reading and digitizing processes. This is not trivial but can be done using additional logic and timing circuits (see, for example, ref. 107). 

Kahlow MA, Jarzeba W, DuBruil TP, Barbara PF. Ultrafast emission spectroscopy in the ultraviolet by time-gated upconversion. Rev. Sci. Instrum. 1988 59 1098-1109. 

In TERS microscopy and spectroscopy, the tip enhancement due to the SPP resonance plays the most essential role both for signal sensitivity and spatial resolution. However, the tip-enhancement effect is not the only one affecting Raman spectra. There coexist other interaction mechanisms between a metal tip and sample molecules, chemical interactions similar to SERS [120-122], and, in addition, mechanical interactions (see Sect. 5.4.1). The latter two interactions show up only when sample molecules are in a close vicinity of a tip. In the TERS system using a ccaitact mode AFM, an experimentally observed TERS spectrum is a complex combination of the contributions of these three interactions, which makes it difficult to interpret experimental TERS spectra. Therefore, elucidation and discrimination of the tip-sample interactions are of scientific and practical importance. This can be realized by measuring a tip-sample distance dependence of TERS, since those three interaction mechanisms have different dependencies on the tip-sample distance. The active control of the distance between the tip and sample is a unique feamre only possible in TERS not in SERS. Two system configurations, time-gated detection and timegated illumination, are described below. 

To present our methodology, we describe the time-gated excitation-emission spectroscopic system in Section 32.3. 2D fluorescence spectroscopy acquiring excitation and fluorescence spectra has been widely used at research and diagnostic levels because of the high selectivity and simple configuration of the measurement system [12-16]. Here, we extended it to the 3D (Ex, Em, and x) system with a time-resolution of200 ps, by a combination of a spatially dispersed super continuum as the... 

Time-Gated Excitation-Emission Matrix Spectroscopy... 

Figure 32.1 (a) A schematic illustration of time-gated excitation-emission matrix spectroscopy, (b) A typical example of the 3D fluorescence data measured for Rhodamine 590 in ethanol... 

The silicon intensified target (SIT) vidicon has a number of unique properties which make it a valuable detector for atomic spectroscopy. The SIT vidicon provides two-dimensional photoelectric detection with high sensitivity and rapid signal readout. Time resolution can be obtained in a time-resolved (real time) mode on the millisecond scale and in a time-gated (equivalent time) mode on the submicrosecond scale. 

For simple RSSF UV-visible spectroscopy, the SPD linear array is adequate for a wide variety of applications (see Section 2). The MCP-SPD linear array should extend the useful wavelength range and signal detection limits to make possible studies in the UV region between 200 and 300 nm, studies at higher scan rates and studies where the signal intensity is low. Gating on a nanosecond time scale also renders these detectors suitable for use in a variety of time-resolved spectroscopies. 

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