Intensity laser spectroscopy

While a laser beam can be used for traditional absorption spectroscopy by measuring / and 7q, the strength of laser spectroscopy lies in more specialized experiments which often do not lend themselves to such measurements. Other techniques are connnonly used to detect the absorption of light from the laser beam. A coimnon one is to observe fluorescence excited by the laser. The total fluorescence produced is nonnally proportional to the amount of light absorbed. It can be used as a measurement of concentration to detect species present in extremely small amounts. Or a measurement of the fluorescence intensity as the laser frequency is scaimed can give an absorption spectrum. This may allow much higher resolution than is easily obtained with a traditional absorption spectrometer. In other experiments the fluorescence may be dispersed and its spectrum detennined with a traditional spectrometer. In suitable cases this could be the emission from a single electronic-vibrational-rotational level of a molecule and the experimenter can study how the spectrum varies with level. 

In FT-Raman spectroscopy the radiation emerging from the sample contains not only the Raman scattering but also the extremely intense laser radiation used to produce it. If this were allowed to contribute to the interferogram, before Fourier transformation, the corresponding cosine wave would overwhelm those due to the Raman scattering. To avoid this, a sharp cut-off (interference) filter is inserted after the sample cell to remove 1064 nm (and lower wavelength) radiation. 

In the present work, we have examined poly(N-vinylcarbazole) (abbreviated hereafter as PVCz) and pyrene-doped poly(aethyl methacrylate) (PMMA) films by using a tine-resolved fluorescence spectroscopic aethod. Fluorescence spectra and their dynanic behavior of the forner fila were elucidated with a high intensity laser pulse and a streak camera, which nakes it possible to neasure dynaaics just upon laser ablation. This aethod reveals aolecular and electronic aspects of laser ablation phenomena (17). For the latter fila a laser pulse with weak intensity was used for characterizing the ablated and Basked areas. On the basis of these results, we demonstrate a high potential of fluorescence spectroscopy in aolecular studies on laser ablation and consider its mechanism. Experimental... 

The use of an Intense laser light source with biological materials Is accompanied by the concomitant problems of localized sample heating and the possibility of protein denaturetlon. A further complication Introduced by resonance Raman spectroscopy Is the Increased potential for photochemical destruction of chromo-phorlc metal centers as a result of the absorption of large amounts of Incident radiation. Both of these situations may be ameliorated by freezing samples to liquid nitrogen temperature ( 90 K), while the even lower temperatures made possible with a closed-cycle... 

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). 

Recently, the electron-transfer kinetics in the DSSC, shown as a schematic diagram in Fig. 10, have been under intensive investigation. Time-resolved laser spectroscopy measurements are used to study one of the most important primary processes—electron injection from dye photosensitizers into the conduction band of semiconductors [30-47]. The electron-transfer rate from the dye photosensitizer into the semiconductor depends on the configuration of the adsorbed dye photosensitizers on the semiconductor surface and the energy gap between the LUMO level of the dye photosensitizers and the conduction-band level of the semiconductor. For example, the rate constant for electron injection, kini, is given by Fermi s golden rule expression ... 

An intense femtosecond laser spectroscopy-based research focusing on the fast relaxation processes of excited electrons in nanoparticles has started in the past decade. The electron dynamics and non-linear optical properties of nanoparticles in colloidal solutions [1], thin films [2] and glasses [3] have been studied in the femto- and picosecond time scales. Most work has been done with noble metal nanoparticles Au, Ag and Cu, providing information about the electron-electron and electron-phonon coupling [4] or coherent phenomenon [5], A large surface-to-volume ratio of the particle gives a possibility to investigate the surface/interface processes. 

Some of the experimental difficulties of Raman spectroscopy are associated with fluorescence, the heat generated by the intense laser beam, and, sometimes, the alignment of the scattered radiation. 

The energy released as heat in the course of the nonradiative decay of P to the ground state and detected as a pressure wave by laser-induced optoacoustic spectroscopy (LIOAS) exhibits positive deviations (i.e., a> 1 cf. Eq. (1)) from the values which were calculated on the basis of the absorption spectrum of Pr alone (Figure 15) [90,115]. This indicates that already within the 15-ns duration of the excitation flash, one or several intermediates must have been formed. These in turn, within the same interval, may again absorb light from an intense laser flash and (at least in part) dissipate heat upon their return to the ground state of the same species (internal conversion) and/or to Pr (photochemical back reaction). The formation of primary photoproducts within the nanosecond flash duration was of course to be expected in view of the much shorter lifetimes of the photochromic fluorescence decay compo-... 

Laser spectroscopy of the 1S-2S transition has been performed by Mills and coworkers at Bell Laboratories (Chu, Mills and Hall, 1984 Fee et al, 1993a, b) following the first excitation of this transition by Chu and Mills (1982). Apart from various technicalities, the main difference between the 1984 and 1993 measurements was that in the latter a pulse created from a tuned 486 nm continuous-wave laser with a Fabry-Perot power build-up cavity, was used to excite the transition by two-photon Doppler-free absorption, followed by photoionization from the 2S level using an intense pulsed YAG laser doubled to 532 nm. Chu, Mills and Hall (1984), however, employed an intense pulsed 486 nm laser to photoionize the positronium directly by three-photon absorption from the ground state in tuning through the resonance. For reasons outlined by Fee et al. (1993b), it was hoped that the use of a continuous-wave laser to excite the transition would lead to a more accurate determination of the frequency interval than the value 1233 607 218.9 10.7 MHz obtained in the pulsed 486 nm laser experiment (after correction by Danzmann, Fee and Chu, 1989, and adjustment consequent on a recalibration of the Te2 reference line by McIntyre and Hansch, 1986). 

Bandrauk s long-term research interests include the dressed-state representation of molecular spectroscopy. His contributions to the nonperturba-tive treatment of molecular spectroscopy from the weak field to strong field limits have been summarized in two chapters in a book he edited in 1993.286 Bandrauk and his coworkers published the first theoretical demonstration of the use of chirped pulses to effect laser bond breaking in less than a picosecond.287 His other firsts include the first prediction of molecular stabilization in intense laser fields288 and the first complete non-Born-Oppenheimer calculation of dissociative ionization of molecules in intense femtosecond laser pulses.289... 

Application of X-Ray Spectroscopy to the Study of Energy Transport in Plasma Produced by an Ultrahigh-Intensity Laser... 

Summary. X-ray line emissions from ultrashort high-intensity laser-produced plasma were studied in order to clarify the physics of energy transport associated with the generation of ultrashort X-ray pulses for use in various applications. This article reviews two topics. The first is the application of Ka spectroscopy to the study of energy transport in laser-produced plasma. The second topic is the application of X-ray polarization spectroscopy to measurements of the anisotropy of hot electrons generated with ultrashort high-intensity laser pulses. 

The interaction of an ultrahigh-intensity laser with a dense plasma is of wide interest, as these lasers open up new horizons for research, such as fs X-ray radiation probing [1,2], energetic particle acceleration [3], and inertial confinement fusion [4,5]. A new spectroscopic method that provides the kind of time- and space-resolved information required to obtain a more quantitative understanding of energy deposition than that provided by particle measurements has been under development [5-8]. Because of the relatively low temperatures that can be accessed with current lasers, conventional K-shell line spectroscopy using near-fully ionized plasma is not suitable. 

In summary, energy transport in ultrahigh-intensity laser-produced plasmas has been investigated via Ka line spectroscopy. No significant differences were found between plastic (representing an insulator) and metallic (repre-... 

Nishimura H, Kawamura, Matsui T, Ochi Y, Okihara S, Sakabe S, Koike F, Jhozaki T, Nagatomo H, Mima K, Uschmann I, Forster E (2003) K spectroscopy to study energy transport in ultrahigh-intensity laser-produced plasmas. J Quantit Spectrosc Ra 81 327-337... 

The origin of Raman spectra is markedly different from that of IR spectra. In Raman spectroscopy, the sample is irradiated by intense laser beams in the UV-visible region (v0), and the scattered light is usually observed in the direction perpendicular to the incident beam (Fig. 1-7 see also Chapter 2,... 

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