Laser thermal addressing

D. Maydan, H. Melchior and F. Kahn, Liquid Crystal Graphic Displays Thermally Addressed by Infrared Laser Beams, IEEE Conference Record of 1972 Conference on Display Devices,... 

In the same way that the molecules of N phases can be electrically reoriented, the molecules of the smectic phase can be dielectrically reoriented by electric fields, albeit at a higher voltage. However, unlike in the N phase, when the field is removed, the bulk viscosity of the smectic phase inhibits relaxation and bistability is favored. This can be an advantage unless the procedure has to be reversed, because this cannot be achieved so easily. Reversal is accomplished by heating to either the less viscous N or isotropic liquid phases (as used in the laser and thermally addressed devices) or by causing electrohydrodynamic scattering to occur (see Sec. 3.6). In this section we shall specifically consider the dielectric reorientation effect. In itself it may not be particularly useful, but when combined with other techniques, it can lead to interesting devices. 

Mass spectrometry requires that the material being studied be converted into a vapor. Great strides have been taken in recent years to address this problem, especially in enticing large, thermally fragile (bio)molecules into the vapor state. Matrix assisted laser ionization-desorption (MALDI) and electrospray ionization (ESI) are two current forefront methods that accomplish this task. Even components of bacteria and intact viruses are being examined with these approaches. John B. Fenn and Koichi Tanaka shared in the award of a Nobel Prize in 2002 for their respective contributions to development of electrospray ionization and soft laser desorption. 

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. 

Analyzer safety There are several potential safety hazards, and the source is one - providing localized temperatures in the range of 1100-1500 K. The laser and its power supply, which is a potential high voltage spark hazard, are other examples. Methods for thermal isolation and instrument purging can address the source issues. The discharging of any charge within the capacitance circuitry of the laser power supply addresses the spark hazard issue. 

The interaction of intense laser pulses with molecular materials is, in general, quite complex. It is customary to delineate the induced processes in three types, namely thermal, photochemical, and photomechanical. Though this formalistic division provides a convenient basis for the discussion of the mechanisms and effects of UV ablation of polymers, the three phenomena are certainly closely interrelated. The inadequacies of this division will be most clearly illustrated in the examination of the chemical effects. The present review addresses all three types of side effects, but the major emphasis concentrates on the photochemical phenomena. 

There is another factor that may be involved and which has not been adequately addressed in the literature. As indicated above, Eq. 1 suggests the extent of photofragmentation and photoproduct formation in the remaining substrate to be constant with laser fluence (for F>Fthr). However, this neglects the possibility that fragments weakly bound to the matrix and/or photoproducts that are formed within the thermally affected zone below the... 

Laser emission with pumping at 946 nm due to the " l9/2(5) " p3/2(l) transition, as shown in Fig. 9.2 [33], with the lowest quantum defect, was observed in Nd YAG crystal [34]. However, the low thermal population of the Z5 level at room temperature led to a low efficiency with respect to the incident pump power. Although this problem could be addressed by increasing temperature, there is another concern of thermalization of the emitting level of... 

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