Chemical laser action

The distribution generated by surprisal analysis is meant to reproduce the results of actual interest, a typical example being the distribution of vibrational energy of products, which is of interest say for chemical laser action. [3] The distribution is not meant to reproduce the fully detailed distribution in classical phase space, which, as already noted, has a to be a highly correlated and complicated distribution. 

The only nonhydride molecule to have been excited directly to chemical laser action is CO. When mixtures of CS2 + Oa are flash photolyzed [236, 237], or subjected to a pulsed electrical discharge [238], oscillation occurs on vibration-rotation lines in a wide range of CO fundamental bands. Infrared emission experiments [239, 240] have established that the reaction mechanism is... 

Chemical laser action has so far been restricted to the molecules HF, HC1, HBr and their denterated analogs and to CO. Lasing has also been stated in a brief report to occur in the OH radical produced in the O3/H2 photolysis 105). The pumping scheme is likely to be... 

Figure 3.24 shows a schematic diagram of experimental apparatus employed by Rice and co-workers for the initiation of chemical laser action in a large variety of metal oxides and metal halides. Their approach was to use an exploded metal wire technique to vaporize and disperse metal atoms into several torr of a surrounding gaseous oxidizer. This was accomplished with use of a capacitor discharge through either a thin metal film on the inner walls of the laser tube or through a metal wire located along the optical axis as shown in Figure 3.24. This method permitted vaporization, mixing, and chemical reaction to occur on the time scale of a few microseconds. This time scale is shorter than the time for substantial radiative or...

A review on laser action in chelates has been given by A. Lempicki, H. Samelson, and C. Brecher, Appl. Opt., Suppl. 2 Chemical Lasers, 205 (1965). 

F+Ha HF- +. H AH =-139.9 kj is also exothermic and can produce energy rich HF molecules. The heat of chemical reaction is distributed in various vibrational-rotational modes to give vibrationally excited HF or HC1 in large numbers. Emission from these hot molecules can be observed in the infrared region at h 3.7 (j-m. The reaction system in which partial liberation of the heat of reaction can generate excited atoms or molecules is capable of laser action (Section 3.2.1). They are known as chemical lasers. The laser is chemically pumped, without any external source of radiation. The active molecule is born in the excited state. Laser action in these systems was first observed by Pimental and Kasper in 1965. They had termed such a system as photoexplosion laser. 

Although the novelty of observing chemically produced vibrational excitation provided an initial impetus, the main purpose of the studies to date has been to determine in detail the relative proportions of excited molecules in the various energy states, the fraction of the reaction energy that goes into internal excitation, which products are excited, and the fate of the excited molecules. Such data are used as aids in the construction of potential energy surfaces to be used, in turn, to describe the dynamics of the reactions. In short, the studies have been in the hands of kineticists. As interest in the subject has spread, more attention has been paid to applications laser action and the reactions of the excited molecules. 

Population inversions have been observed in a number of chemical and photochemical reactions. In a few of these cases, laser action has been produced in a suitable cavity. In most cases of molecular laser emission, there is only partial inversion282 in which several vibration-rotation transitions are inverted even though the total population in the upper vibrational state does not exceed that in the lower. In this case there is laser action in P branch transitions only. 

Laser action is observed on vibration-rotation transitions of CO in the flash photolysis of CS2 + 02 mixtures61. Ay = 1 transitions are observed with y in the range 6-14. Only P branch lines are observed, as usual. The excitation is presumably chemical rather than by energy transfer to ground state CO. A suggested mechanism involves... 

Non-equilibrium excitation in flames has been discussed from the point of view of possible inversions286. The possibility of laser action on several transitions of CN excited in active nitrogen has been discussed292 in terms of relevant rate equations and the threshold condition for oscillation. A chemical laser is of course a physical phenomenon, the performance of which depends critically on the rate... 

Laser devices have become of great importance in chemical studies and applications and, before discussing some of the applications of lasers in kinetic measurements, it is worth reviewing the fundamental characteristics of a laser. Many different substances have been found to exhibit laser action when suitably pumped and lasers are now available at thousands of wavelengths from the vacuum ultraviolet to the submillimeter wave region. Figure 1 shows some of the lasers which can be used in... 

So, the studied liquids absorb 1+2 photons, but to excite their molecules first electron levels it needs 5-6 photons because they are in the region of 180-220nm. Therefore one may assume that vibrational levels excitation ( 2ev) occurs which is enough to realize chemical reactions with formation of new, as well gas like products in condensed mediums. It is probable that the nature of reactions products will depend on the stimulation mechanism thermal way or induced by high intensivity laser action. So such studies are actual because they are opening new ways to realize purposeful reactions, in particular synthesis. 

Chemical lasers are pumped by reactive processes, whereas in photodissociation lasers the selective excitation of certain states and the population inversion are directly related to the decomposition of an electronically excited molecule. Photolysis has been the only source of energy input employed in dissociation lasers, although it appears quite feasible to use other energy sources, e.g. electrons, to generate excited states. Table 4 lists the chemical systems where photolysis produces laser action. It is appropriate to begin the discussion of Table 4 with the alkali-metal lasers since Schawlow and Townes in 1958 35> chose the 5 f> 3 d transitions of potassium for a first numerical illustration of the feasibility of optical amplification. These historical predictions were confirmed in 1971 by the experimental demonstration of laser action in atomic potassium, rubidium and cesium (Fig. 14). 

The carbon-monoxide chemical laser exhibits a variety of pumping reactions. Laser action was first reported by Pollack in CS2/02 photolysis 125>. The pumping scheme in this case is believed to be the following 126> ... 

FIGURE 7-5 Four processes important in laser action (a) pumping (excitation by electrical, radiant, or chemical energy), (b) spontaneous emission, (c) stimulated emission, and (d) absorpiion. 

Transparent colored YAG ceramics doped with Ti and Zr ions as possible broad-band materials for tunable and ultra-short pulses lasers were obtained. The procedure of doped ceramics fabrication included chemical co-precipitation, precursors heat treatment, YAG powder grinding, high pressure colloidal slip-casting for nanopowders compaction and vacuum sintering of performs at 1730-1800 C. Absorption spectra of Zr ceramics samples are similar to the spectra of correspondingly doped YAG single crystals. Zr luminescence was observed for the first time. Possibility to obtain laser action is discussed. 

This collision-induced dissociation of electronically excited molecules plays an important role in chemical reactions and has therefore been studied for many molecules [1004-1006]. The collision cross sections for this process may be sufficiently large to generate inversion between atomic levels. Laser action based on dissociation pumping has been demonstrated. Examples are the powerful iodine laser [1007] and the Cs laser [1008]. 

Fig. 1.3 Time line of ECL 1964-1965, first experiments 1965, theory 1966, transients 1969, magnetic field effects 1972, Ruffipy) 1977, oxalate 1981, aqueous 1982, Ruibpy) polymer and persulfate 1984, Ru(bpy) label 1987, tri-n-propylamine (TPA) 1989, bioassay 1993, ultramicroelectrodes 1998, laser action 2002, semiconductive nanocrystals (Reprinted with permission from Ref. [1]. Copyright 2008 American Chemical Society)...

Fig. 3. Principle of the light-induced chemical processes leading to laser action of i-C F J. Laser transition at 1.315 yin with a photonenergy of 0.94 eV.

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