UV laser pulsed

Subliming ablators are being used in a variety of manufacturing appHcations. The exposure of some organic polymers to pulsed uv-laser radiation results in spontaneous ablation by the sublimation of a controUed thickness of the material. This photoetching technique is utilized in the patterning of polymer films (40,41) (see PHOTOCHEMICAL TECHNOLOGY). 

The pump beam comes from a laser. The necessity of high light intensity in a short time demands this. Exceptions are possible for relatively unreactive intermediates a flash lamp was used in the first direct detection of a carbene (Closs and Rabinow, 1976), but the availability of modern high-power, pulsed uv-lasers has made this approach obsolete. One requirement then is that the precursor to be irradiated absorb at an available laser frequency. For aromatic carbenes, this is not a restrictive requirement. 

Ablation using radiations of various wavelengths (IR, visible, UV, or x-ray) has been employed to fabricate plastic chips. For instance, photoablation using pulsed UV lasers (193 nm) has been used to fabricate plastic chips out of polyethylene terephthalate (PET, 100 pm thick) [189,190, 258,758] and polycarbonate (PC, 125 pm thick) [189,258]. Channels as narrow as 30 pm and as deep as 100 pm can be made [258,758]. The cross section of a photoablated PET channel plate laminated with another PET using a thin PE adhesive layer was shown in Figure 2.20 [191]. 

The laser flash photolysis technique relies on the use of a pulsed UV laser for the rapid synthesis of the reactive intermediate of interest by photochemical decomposition of a suitable stable precursor, and (most commonly) fast time-resolved UV/VIS spectrophotometry to detect the species and monitor its decay19. The absorbance-time profile so... 

More recently, Weiller (39) has extended this work by performing a detailed rapid-scan FTIR study of M(CO)e (M = Cr or W) in liquid Xe and liquid Kr. A pulsed UV laser source, synchronized to the moving mirror of the FTIR interferometer, was used to photolyze the hexacarbonyls. MCCOsKr was characterized in liquid Kr, Cr(CO)gXe in liquid Xe, and W(CO)sXe in liquid Xe and liquid Kr doped with 5% Xe. M(CO)gKr has... 

It has been shown that pulsed UV-lasers can be used to ablate certain fragments from a zeolite target these fragments can be deposited on a substrate and subjected to a subsequent hydrothermal treatment resulting in crystalline zeolite layers. The initially deposited layers appear to be X-ray amorphous, although they can still be used to nucleate crystals of the original zeolite target material. [73,74,75]... 

Several recent experimental studies in small hydride molecules have indeed demonstrated that molecular rotation is instrumental in accepting the energy. Thus the relaxation in the 4 11 state of NH and ND was examined using pulsed UV laser excitation and time-resolved fluorescence studies. The data showed that, contrary to the energy-gap law predictions, NH relaxes order of magnitude faster than ND. Very similar behavior was observed in the state of OH in solid Ne. ... 

Pulsed, time-resolved photoacoustic calorimetry employs a pulsed uv laser source to induce a photochemical reaction in the molecule of... 

The neutral clusters, C6H4(OH)2 (H20),, are found to be produced in the gas phase by irradiation of the pulsed IR-laser onto the liquid beam. The clusters continue to be released from the liquid beam surface for a period of 10 ps after the pulsed IR-laser irradiation. The dynamics of the cluster release is further examined by observing the neutral species at a certain time after the IR-laser irradiation at a certain distance from the liquid beam. In reality, the neutral species are ionized by the pulsed UV-laser and are mass analyzed by the mass spectrometer. The spatial distribution of the neutral clusters are observed by changing the position of the ionization laser with respect to the liquid beam and the delay time of the UV-laser irradiation from the IR-laser irradiation. 

Applying lasers as the excitation source and either a scanning monochromator coimected to a boxcar integrator or, better, an optical multichannel analyzer for the experimental setup has given rise to the development of the laser-induced fluorescence technique which can be used for diagnostic pmposes in many contexts [37]. Pulsed UV lasers like nitrogen, frequency-tripled Nd YAG or excimer lasers serve as the light source. 

The use of narrower rounded turns for microchip-based SCCE is reported for reducing band broadening at the corners. This approach has been shown to reduce the broadening seen for turns in other microfluidic chip designs. Other, more exotic approaches to reducing dispersion at the turns of channels on microfluidic devices have been reported. One technique using a pulsed UV laser to modify the surface of plastic chips at the turn to increase the EOF by up to 4%. This technique was shown to reduce band broadening at the turns. ... 

Most studies have dealt either with the free radical polymerization of hydrophobic monomers—e.g., styrene [56-89], methyl methacrylate (MMA) [68,73,74,84,86,90-93] or derivatives [2,94,97], and butyl acrylate (BA) [98-100]—within the oily core of O/W microemulsions or with the polymerization of water-soluble monomers such as acrylamide (AM) within the aqueous core of W/O microemulsions [101-123]. In the latter case, the monomer is a powder that has to first be dissolved in water (1 1 mass ratio) so that the resulting polymer particles are swollen by water, in contrast with O/W latex particles, where the polymer is in the bulk state. The polymerization can be initiated thermally, photochemically, or under )>-radiolysis. The possibility of using a coulometric initiation for acrylamide polymerization in AOT systems was also reported [120]. Besides the conventional dilatometric and gravimetric techniques, the polymerization kinetics was monitored by Raman spectroscopy [73,74], pulsed UV laser source [72,78], the rotating sector technique [105,106], calorimetry, and internal reflectance spectroscopy [95]. 

In an aerosol SEC/MALDI experiment, the effluent from the SEC column was combined with a matrix solution and sprayed directly into a MALDI-TOF spectrometer. Ions were formed by irradiation of the aerosol particles with a pulsed UV laser. The ions were separated in a two-stage TOE apparatus, and averaged mass spectra were stored throughout the SEC/MALDI experiment. The matter of coupling MALDI with SEC has been recently reviewed, and it was concluded that off-line SEC/MALDI is routine today, whereas considerable work is still necessary in order to make on-line SEC/ MALDI a viable alternative to the off-line method. ... 

Wong, W., Chan, K., Yeung, K.W., Lau, K.S., 2000b. Pulsed UV laser and low temperature plasma modification on polyester microfiber effect of dyeing properties. J. Text. Eng. 46 (2), 32 1. 

V. APPLICATIONS OF LASER IONIZATION MASS AND PHOTOELECTRON SPECTROSCOPY A. Photochemistry with Intense, Pulsed UV Laser Excitation... 

Intense, pulsed UV lasers provide a very different photochemical excitation source. Because of rate of absorption can sometimes exceed the rate of photochemical processes, some systems can be driven to high energies, giving products not otherwise expected. Laser ionization mass spectrometry is ideally suited to the study of this new type of photochemistry. Scanning the laser wavelength can produce the MPI optical spectrum of the products and these spectra can be identified with specific mass fragments from the mass spectrum as described in Section III. 

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