Infrared-laser-induced thermal

The term 1 or h indicates low or high coverage of adsorbed ethene, as inferred from ethene exposures.h TPD, temperature-programmed desorption LITD, laser-induced thermal desorption 1 FT-MS, Fourier-transform mass spectrometry SIMS, secondary-ion mass spectrometry MS, mass spectrometry T-NEXAFS, transient near-edge X-ray absorption fine structure spectroscopy RAIRS, reflection-absorption infrared spectroscopy. d Data for perdeut-erio species.1 Estimated value. 

Becaii.se of the phenomenon of self-absorption the ideal sample for conventional emission studies is a thin layer (e.g.. a polymer film), on both metal and semiconductor. surfaces [81]. A sample is usually heated from below the emitting surface, the lower surface thus having a higher temperature than the upper one. Therefore, radiation emitted from below the upper surface is absorbed before it reaches the surface, and this self-absorption of previously emitted light severely truncates and alters features in the emission spectra of optically thick samples. This problem is overcome by using a laser for controlled heat generation within a thin surface layer of the sample, self-absorption of radiation thus being minimized. These methods, known as laser-induced thermal emission (LITE) spectroscopy [85], [86] and transient infrared emission spectroscopy (TIRES) [87], [88] can produce analytically useful emission spectra from optically thick samples. Quantitative applications of infrared emission spectroscopy are described in [89]-[91]. 

Handschuh M, Nettesheim S, Zenobi R (1999) Is infrared laser-induced desorption a thermal process The case of aniline. J Phys Chem B 103(10) 1719-1726... 

In principle, also a laser infrared pulse should be able to deposit sufficient energy into the vibration of the adsorptive bond so that the molecule desorbs. However, the vibration of the adsorptive bond will be very enharmonic, particularly at high excitation, so that desorption induced by monochromatic infrared will be very unlikely, except at enormous laser intensities, calculated to be in the order of >10 Wcm". (3) In addition there must be considerable broadening of the vibrational energy levels of the adsorptive bond. Then process (2) is of little resonant character. In general process (3), the direct interaction between the adsorbent and laser infrared, will heat up the system leading to thermal desorption. This is particularly true for metals, where extremely fast relaxation of electronic excitation into the phonon bath within lO s takes place. Laser induced thermal desorption is possible at all laser frequencies at which appreciable absorption of light occurs in the adsorbent.(4)... 

Lindquist, R. G., P. G. LoPresti, and I. C. Khoo. 1992. Infrared and visible laser induced thermal and density optical nontinearities in nematic and isotropic liquid crystals. Proc. SPIE Int Soc. Opt Eng. 1692 148. 

If the system under consideration is chemically inert, the laser excitation only induces heat, accompanied by density and pressure waves. The excitation can be in the visible spectral region, but infrared pumping is also possible. In the latter case, the times governing the delivery of heat to the liquid are those of vibrational population relaxation. They are very short, on the order of 1 ps this sort of excitation is thus impulsive. Contrary to a first impression, the physical reality is in fact quite subtle. The acoustic horizon, described in Section VC is at the center of the discussion [18, 19]. As laser-induced perturbations cannot propagate faster than sound, thermal expansion is delayed at short times. The physicochemical consequences of this delay are still entirely unknown. The liquids submitted to investigation are water and methanol. 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

Experiments were conducted in our laboratory to evaluate many of the dynamical expectations for rapid laser heating of metals. One of the aims of this work was to identify those population distributions which were characteristic of thermally activated desorption processes as opposed to desorption processes which were driven by nontbennal energy sources. Visible and near-infrared laser pulses of nominally 10 ns duration were used to heat the substrate in a nonspecific fashion. Initial experiments were performed by Burgess etal. for the laser-induced desorption of NO from Pt(foil). Operating with a chamber base pressure 2 x 10 torr and with the sample at 200 K, initial irradiation of a freshly cleaned and dosed sample resulted in a short time transient (i.e. heightened desorption yield) followed by nearly steady state LID signals. The desorption yields slowly decreased with time due to depletion of the adsorbate layer at the rate of ca. 10 monolayer... 

The observation of blackbody-radiation-induced thermal dissociation of gaseous cluster ions suggests that very low power, CW infrared laser irradiation should also... 

The thermal, unsensitized infrared laser, and SiF4 laser sensitized decomposition of 1,2-dichloropropane were described by Tsang and coworkers96. The dichloro substrate yielded via four reaction channels 3-chloropropene, cw-l-chloropropene, trans- 1-chloro-propene and 2-chloropropene. These products have also been observed in thermal and laser-induced processes. Comparative data of the dichloropropane decomposition between the laser-induced experiment and the other pyrolytic methods indicated the former to be associated with complex phenomena with infrared multiphoton-induced decomposition. Consequently, a wide range of processes appeared to occur and the unimolecular rate parameters can be unambigously interpreted only at definite high pressure. 

It was supposed that, because of a rapid intramolecular energy pooling, infrared laser multiphoton decomposition at low laser fluence usually proceeds via the energetically most favourable reaction channel [26], From the material balance of gaseous decomposition products (Fig. 2) it was inferred that there are common primary steps for both the thermal and the explosive laser-induced decomposition of (fluoromethyl)silanes. 

CVD can also be classified using its activation methods. Thermal activated CVD processes are initiated only with the thermal energy of resistance heating, RF heating or by infrared radiation. They are widely used to manufacture the materials for high-temperature and hard-to-wear applications. In some cases enhanced CVD methods are employed, which includes plasma-enhanced CVD (PECVD), laser-induced CVD (LCVD), photo CVD (PCVD), catalysis-assisted CVD and so on. In a plasma-enhanced CVD process the plasma is used to activate the precursor gas, which significantly decreases the deposition temperature. 

Abstract—"TYm origins and the dynamics of optical nonlinearities in nematic liquid crystal films, namely, laser-induced molecular reorien-tational and thermal refractive index changes, are analyzed in the context of optical wave mixings. Theoretical expressions for the basic non-linearities, the rise and decay time, diffraction efficiencies, and other pertinent parameters involved in the dynamic grating formation are derived. Experimental results obtained with visible and infrared laser pulses are analyzed. Some newly observed novel nonlinear processes are also reported. 

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