Pulsed main beams

As a result of this study, it should be apparent that both C.W. and pulsed laser beams are capable of very efficiently initiating the cross-linking polymerization of multifunctional acrylate photoresists, provided adequate initiators are used to absorb the laser photons and generate the reactive species. The main advantages of this technology arise from the specific properties of the laser emission ... 

The pulsed primary beam is passed through a skimmer into the main chamber a chopper wheel located after the skimmer and prior to the collision center selects a slice of species with well-defined velocity that reach the interaction region. This section of the beam then intersects a pulsed reactant beam released by a second pulsed valve under well-defined collision energies. It is important to stress that the incorporation of pulsed beams allows that reactions with often expensive (partially) deuterated chemicals be carried out to extract additional information on the reaction dynamics, such as the position of the hydrogen and/or deuterium loss if multiple reaction pathways are involved. In addition, pulsed sources allow that the pumping speed and hence costs can be reduced drastically. 

In the first reported measurements made with picosecond pulses, an optical beam splitter was used to pick off a portion of the pulse train and a variable optical delay path was introduced between the two beams [7]. The main beam was used to excite (pump) a dye sample, and the weak (probe) beam was used to monitor the recovery of dye transmission as a function of delay. Over the past two decades, this pump-probe method has been extended to a variety of measurement geometries and used to measure electronic polarization dephasing times as well as population lifetimes. 

Fig. 1.52. Typical experimental setup for a pulsed molecular beam experiment for studying the catalytic properties of size-selected clusters on surfaces. It mainly consists of a pulsed valve for the generation of a pulsed molecular beam and a differentially pumped, absolutely calibrated quadrupole mass spectrometer. The length of the valve extension tube is adjusted to obtain a beam profile of similar dimensions as the sample under investigation. A typical time profile is also shown. It can be adjusted up to continuous operation. The pulse-to-pulse stability is better than 1%...

It appears to us worthwhile to point out the different parameters relevant to the analysis of the tlrird-order nonlinear optical response of nanocomposite materials, because some of them are sometimes omitted in the literature, rendering the comparison difficult. They can be classified into two main sets. First, some parameters are linked wltlr the optical excitation source, which usually consists of a pulsed laser beam Wavelength X, pulse energy E, pulse duration t, repetition rate v. Secondly, otlrer relevant parameters concern the material Itself Particle size and shape (and distributions), metal volume fraction p, particle spatial arrangement in the host medium. 

Figure 17.1.21 Experimental apparatus for SHG experiments. A small portion of the beam from a high-power pulsed laser is sent to a reference channel, after frequency doubling, to provide a signal to normalize for fluctuations in the laser intensity. The main beam is linearly polarized and filtered before impinging on the sample. The resulting beam at 2

We have investigated in detail the parameters affecting the continuous y-radiolysis of concentrated solutions (intensity, pH, 02, scavengers, etc.). Transients were investigated by pulsed electron beam radiolysis and kinetic spectroscopy, and the reactions of the optically accessible excited states of nitrate were investigated by conventional photolysis. This paper represents a survey of our recent results which, taken in conjunction with the work of others, allows the construction of a model whereby the main features of this system may be understood and may even be predicted. Literature review is necessarily selective for the present purpose (because of doubtful relevance to liquid state processes, low temperature radiolysis, and hence ESR work has been omitted from... 

The technical principle of MALDl imaging is summarized in Figure 4.1. A pulsed laser beam is focused to the size of the aspired lateral resolution. To date, mainly lasers with ultraviolet wavelengths (337, 355, and 266 nm) and pulse lengths of a few nanoseconds have been used. The focused laser beam is directed to the surface of the sample, which is then moved in steps in order to scan the sample according to the intended lateral resolution of the system. Before analysis, the sample must be prepared in such a way that the biomolecular ions can be desorbed and ionized by the laser beam, as in regular MALDl analyses. To achieve this, the sample (e.g., a biological tissue sample) must be covered with a suitable matrix, such as 2,5-dihydroxybenzoic acid (DHB), sinapinic acid (SA) or... 

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