Pulsed light

The low MW power levels conuuonly employed in TREPR spectroscopy do not require any precautions to avoid detector overload and, therefore, the fiill time development of the transient magnetization is obtained undiminished by any MW detection deadtime. (3) Standard CW EPR equipment can be used for TREPR requiring only moderate efforts to adapt the MW detection part of the spectrometer for the observation of the transient response to a pulsed light excitation with high time resolution. (4) TREPR spectroscopy proved to be a suitable teclmique for observing a variety of spin coherence phenomena, such as transient nutations [16], quantum beats [17] and nuclear modulations [18], that have been usefi.il to interpret EPR data on light-mduced spm-correlated radical pairs. 

Taub AF (2003) Treatment of rosacea with intense pulsed light. J Drugs Dermatol 2 254-259... 

Mark KA, Sparacio RM, Voigt A, et al (2003) Objective and quantitative improvement of rosacea-associated erythema after intense pulsed light treatment. Dermatol Surg 29 600-604... 

Chan HH, Kono T (2004) The use of lasers and intense pulsed light sources for the treatment of pigmentary lesions. Skin Therapy Lett 9(8) 5-7... 

A novel method called pulsed light assisted electrodeposition (PLAE), involving the alternate depositions of two elements to form a compound semiconductor, one by electrochemical and the other by photoelectrochemical deposition, should be referred to in this context. Takahashi et al. [108] suggested that high-quality... 

Fig. 4.11 Schematic representation of the pulsed light assisted electrodeposition of CdTe. (a) Deposition of one Te monolayer in the dark (b) deposition of one Cd monolayer under illumination. (Reproduced with permission from [108], Copyright 2009, American Institute of Physics)...

Takahashi M, Todorobaru M, Wakita K, Uosaki K (2002) Heteroepitaxial growth of CdTe on a p-Si(lll) substrate by pulsed-light-assisted electrodeposition. Appl Phys Lett 80 2117-2119... 

Integration of this equation yields the time evolution of the concentration of excited molecules [JA ]. Let [1A ]0 be the concentration of excited molecules at time 0 resulting from pulse light excitation. Integration leads to... 

Sinusoidal excitation provides only one harmonic at the modulation frequency. In contrast, pulsed light provides a large number of harmonics of the excitation repetition frequency. The harmonic content, the number of harmonics and their amplitude, is determined by the pulse width and shape.(25) For example, a train of infinitely short pulses provides an infinite number of harmonics all with equal amplitude. A square wave provides only three modulation frequencies with sufficient amplitude to be usable. Equation (9.74) gives the harmonic content of a train of rectangular pulses R(t) of D duty cycle (pulse width divided by period) and RP peak value ... 

In phase-modulation fluorometry, the pulsed light source typical of time-domain measurements is replaced with an intensity-modulated source (Figure 10.5). Because of the time lag between absorption and emission, the emission is delayed in time relative to the modulated excitation. At each modulation frequency (to = 2nf) this delay is described as the phase shift (0, ), which increases from 0 to 90° with increasing modulation frequency. The finite time response of the sample also results in demodulation to the emission by a factor m which decreases from 1.0 to 0.0 with increasing modulation frequency. The phase angle (Ow) and the modulation (m, ) are separate... 

E. Soini, Pulsed light, time-resolved fluorometric immunoassay, in Monocolonal Antibodies and New Trends in Immunoassays (Ch. A. Bixollon, ed.) pp. 197-208, Elsevier Science Publishers, Amsterdam (1984). 

Figure 5.23 The scheme of an experimental arrangement for PA spectroscopy. The inset shows a typical PA signal generated as a result of illuminating an absorbing sample with pulsed light.

A Gd + doped crystal is illuminated with a pulsed light source, so that the l7/2 excited state of this ion is populated by absorbing 1 mJ of energy per incident pulse. Determine the heat delivered to the crystal per excitation pulse if the nonradiative rate from this state is 10 s The fluorescence lifetime of the l7/2 state is 30 /xs. 

Fig. 15 Photo-induced current of aligned-DNA films (20 x 10 mm, thickness 30 5 irm) in which one acridine orange intercalates per ca. 10 base-pairs, a At 0.01 V, b 0.05 V, and c 0.1 V of applied voltage to the comb electrodes, in which the DNA strands are aligned perpendicular to the two electrodes, d DNA strands in the film placed parallel to the two electrodes at 0.1 V applied voltage. The pulse light above 380 nm was irradiated from a 150 W xenon lamp at 25 °C...

With its high peak power, pulsed light penetrates opaque materials more effectively than does continuous light. 

Figure 23. Outline of a new kind of pulsed light source with the optical ring condenser.

Rather than using short-duration pulsed-light sources, which usually yield information concerning nonequilibrium->equilibrium relaxations, it is often of great interest to study equilibrium- equilibrium relaxations and excitations. This requires the use of step-function light sources. The temporal resolution in this case is determined by the rise time of the step. There are, of course, two types of steps that one need consider (a) a source that is initially off and then is rapidly turned on and maintained on for some time, and (b) a source that is initially on and then is rapidly turned off and then maintained off for some time. 

The resemblance of the photocurrent to the optical adsorption spectrum has suggested the involvement of molecular excited states in the creation of charge carriers. While this resemblance is by no means universally observed, the concept of carrier creation via exciton interactions at or very near the illuminated electrode has become increasingly favored. Many of the data leading to these conclusions have been obtained by the use of pulsed light techniques (6, 7,3). These methods are virtually independent of electrode effects and the subsequent analysis of the transient current has led to considerable advances in the theory of charge transfer in molecular crystals. 

Biphotonic processes depend greatly on light intensity, and on the lifetimes of the excited states M. Their importance increases markedly in conditions of very intense, pulsed light excitation, e.g. in laser beams or in flash light. 

Figure 7.34 Principle of kinetic single-photon counting. L, pulsed light source S, sample P, photodiode F, interference filter or monochromator D, photomultiplier R, voltage ramp generator (1 to start the ramp, 0 to stop it). The voltage V is fed into a multichannel analyser M. Inset voltage ramp V(t)...

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