Single photon spectroscopy

Thus for naphthalene, the transition (A) is forbidden for single photon spectroscopy both for x study polarized process, the transition moment ... 

The results for Eu " in CaF2 and SrF2 are even more interesting, since the excited 4/ levels cannot be observed by single-photon spectroscopy due to the overlap by the 4/ 5d band. At the same time, the lower position of the 4/ 5d states for Eu " relative to Gd increases the absolute two-photon absorption strength. 

In this connection (as already hinted above), an interesting experimental possibility arises. The symmetry of an autoionising resonance (but not its width) depends on the mode of excitation. Thus, for example, for an atom with an s2 ground state, one may excite the same autoionising resonances either directly by single-photon spectroscopy, or by stepwise excitation via an intermediate, excited msns 1So state, which can be reached by a two-photon transition [441], In the latter instance, the symmetries of the lines can be dramatically altered, and in the present theory, this... 

Fig. 9.3. The Q-reversal effect in multiphoton ionisation. Note that Q stands for the generalised asymmetry parameter in multiphoton spectroscopy, as opposed to q in single-photon spectroscopy. The choice of parameters corresponds to REMPI of K (see text - after J.-P. Connerade and A.M. Lane [385]).

Both methods therefore complement each other in high-resolution laser spectroscopy in the vacuum ultraviolet region, where single-photon spectroscopy is impeded by lack of tunable lasers. With intense light of a pulsed... 

All the previous discussion in this chapter has been concerned with absorption or emission of a single photon. However, it is possible for an atom or molecule to absorb two or more photons simultaneously from a light beam to produce an excited state whose energy is the sum of the energies of the photons absorbed. This can happen even when there is no intemrediate stationary state of the system at the energy of one of the photons. The possibility was first demonstrated theoretically by Maria Goppert-Mayer in 1931 [29], but experimental observations had to await the development of the laser. Multiphoton spectroscopy is now a iisefiil technique [30, 31]. 

Zilker S J, Kador L, Friebel J, Vainer Y G, Kol chenko M A and Personov R I 1998 Comparison of photon echo, hole burning, and single molecule spectroscopy data on low-temperature dynamics of organic amorphous solids J. Phys. Chem 109 6780-90... 

Photofragment spectroscopy is extremely sensitive, but it has the disadvantage that one is only sensitive to absorption that leads to photodissociation. For single-photon experiments, this means that one is restricted... 

Photoelectron spectroscopy of free radicals has been utilized for detection of radicals. It can be via resonance photoexcitation and photoionization (e.g. ZEKE) or non-resonance photoionization (e.g. single-photon VUV photoionization). The photoelectron spectroscopy of free radicals has been reviewed in 1994 by Chen.5 A recent review on mass spectrometry, photoelectron spectroscopy, and photoionization of free radicals by Sablier and Fujii is available.72 It is worthwhile to point out that mass spectrometry by photoionization offers some advantage for the detection of radicals, in comparison with the conventional mass spectroscopy by electron-impact... 

Volkmer, A., Hatrick, D. A. and Birch, D. J. S. (1997). Time-resolved nonlinear fluorescence spectroscopy using femtosecond multiphoton excitation and single-photon timing detection. Meas. Sci. Technol. 8, 1339 19. 

Merkel OM, Librizzi D, Pfestroff A, Schurrat T, Buyens K, Sanders NN, De Smedt SC, Behe M, Kissel T (2009) Stability of siRNA polyplexes from poly(ethylenimine) and poly (ethylenimine)-g-poly(ethylene glycol) under in vivo conditions effects on pharmacokinetics and biodistribution measured by Fluorescence Fluctuation Spectroscopy and Single Photon Emission Computed Tomography (SPECT) imaging. J Control Release 138 148-159... 

Summary. This Chapter focuses on the investigation of fast electron transport studies in solids irradiated at relativistic laser intensities. Experimental techniques based upon space-resolved spectroscopy are presented in view of their application to both ultrashort Ka X-ray sources and fast ignition studies. Spectroscopy based upon single-photon detection is unveiled as a complementary diagnostic technique, alternative to well established techniques based upon bent crystals. Application of this technique to the study of X-ray fluorescence emission from fast electron propagation in multilayer targets is reported and explored as an example case. 

D. J. S. Birch and R. E. Imhof, Time-domain fluorescence spectroscopy using time-correlated single-photon counting, in Topics in Fluorescence Spectroscopy (J. R. Lakowicz, ed.), Vol. 1, pp. 1-95, Plenum Press, New York (1991). 

Abbreviations BSA, bovine serum albumin PBS, phosphate buffered saline PMFS, phase-modulation fluorescence spectroscopy TCSPC, lime-correlated single photon counting. 

There are now more than 200 PET centres worldwide and, compared to single photon emission computed tomography (SPECT) or magnetic resonance spectroscopy (MRS), PET is the most sensitive technique and gives quantitative data. While there are currently a wide variety of site-specific and F-radio-... 

In single beam two-photon spectroscopy, an intense laser beam having a frequency hv = l/2(fi2 -E )is passed through the crystal, and the attenuation of the beam is measured. To measure attenuation directly is extremely difficult and it is better to measure the proportional quantity, while the fluorescence maybe the most useful. Two-photon spectroscopy has not been used so far in the luminescence of minerals field, but many relevant centers have been studied in artificial compounds, such as Cr ", Mn, Cu, Ni, Eu (McClure 1990). 

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