Hydrogen lasers

In 1970 the first report of the molecular hydrogen laser opened up a decade of activity in VUV laser development, which included the appearance of rare gas excimer and exciplex lasers and the achievement of tunable coherent radiation in the Lyman-a region via harmonic generation. The surge of activity in the development of VUV lasers arose in part from the uniqueness of the VUV region, in part from the ultimate interest in X-ray lasers and, from our perspective, from the exciting prospects in spectroscopy and molecular dynamics promised by narrow linewidth, tunable, high-power VUV laser pulses for state-selective studies. Here we review the principles on which VUV lasers are based. 

Figure 6.8 The occupation probabilities, an (Tgp j) at the end of the hydrogen—laser pulse interaction (see the caption of figure (6.7)), for the states with n > 2. The numbering of the states that are involved in the calculation is given with njtatesi which counts first the states with = 0, then the states with =1, etc. The probabilities obtained without and with the intrashell interaction matrix elements are shown with open circles and solid squares, respectively. The peaks correspond to the various angular momentum quantum numbers , as shown in the figure.

Various deactivation processes have a strong influence of the power and other characteristics of the laser. All these forms are eombined most favorably in fluoro-hydrogen lasers. Therefore, we consider this system in more detail. 

Another near resonant process is important in the hydrogen fluoride laser, equation (A3.13.37), where vibrational to vibrational energy transfer is of interest ... 

Figure 9.46 shows an example of a fluorescence excitation spectmm of hydrogen bonded dimers of x-tetrazine (1,2,4,5-tetraazabenzene). The pressure of x-tetrazine seeded into helium carrier gas at 4 atm pressure was about 0.001 atm. Expansion was through a 100 pm diameter nozzle. A high-resolution (0.005 cm ) dye laser crossed the supersonic jet 5 mm downstream from the nozzle. 

Fluorine reacts with ammonia in the presence of ammonium acid fluoride to give nitrogen trifluoride, NF. This compound can be used as a fluorine source in the high power hydrogen fluoride—deuterium fluoride (HF/DF) chemical lasers and in the production of microelectronic siUcon-based components. 

Rhenium hexafluoride is used for the deposition of rhenium metal films for electronic, semiconductor, laser parts (6—8), and in chemical vapor deposition (CVD) processes which involve the reduction of ReF by hydrogen at elevated (550—750°C) temperatures and reduced (<101.3 kPa (1 atm)) pressures (9,10). 

Chemica.1 Lasers. Chemical lasers (44) produce a population inversion by a chemical reaction that leaves the product in an excited state. One example is the set of reactions leading to production of excited-state hydrogen fluoride [7664-39-3], HE, according to... 

Laser isotope separation techniques have been demonstrated for many elements, including hydrogen, boron, carbon, nitrogen, oxygen, sHicon, sulfur, chlorine, titanium, selenium, bromine, molybdenum, barium, osmium, mercury, and some of the rare-earth elements. The most significant separation involves uranium, separating uranium-235 [15117-96-1], from uranium-238 [7440-61-1], (see Uranium and uranium compounds). The... 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

Hydrogen transfer in excited electronic states is being intensively studied with time-resolved spectroscopy. A typical scheme of electronic terms is shown in fig. 46. A vertical optical transition, induced by a picosecond laser pulse, populates the initial well of the excited Si state. The reverse optical transition, observed as the fluorescence band Fj, is accompanied by proton transfer to the second well with lower energy. This transfer is registered as the appearance of another fluorescence band, F2, with a large anti-Stokes shift. The rate constant is inferred from the time dependence of the relative intensities of these bands in dual fluorescence. The experimental data obtained by this method have been reviewed by Barbara et al. [1989]. We only quote the example of hydrogen transfer in the excited state of... 

In dimers composed of equal molecules the dimer components can replace each other through tunneling. This effect has been discovered by Dyke et al. [1972] as interconversion splitting of rotational levels of (HF)2 in molecular beam electric resonance spectra. This dimer has been studied in many papers by microwave and far infrared tunable difference-frequency laser spectroscopy (see review papers by Truhlar [1990] and by Quack and Suhm [1991]). The dimer consists of two inequivalent HE molecules, the H atom of one of them participating in the hydrogen bond between the fluorine atoms (fig. 60). PES is a function of six variables indicated in this figure. 

Hydrogen to uranium all isotopes Yes, on a scale of few micrometers depth Yes, depending on the laser irradiance... 

In an attempt to develop the hydrogen bomb before the Russians, a second weapons laboratory , Lawrence Livermore, was established in July 1952 to handle the additional work that would be necessaiy to stay ahead of the Russian nuclear weapons program. The administrator chosen was the University of California. Eor the next forty-five years, this LLNL was a formidable competitor to Los Alamos in the development of nuclear weapons. But much like most of the other major national laboratories, its focus also shifted away from nuclear weapons to basic science to fields like magnetic and laser fusion energy, non-nuclear energy, biomedicine, and environmental science. By the late 1990s, half of the laboratoi y s budget was nonde-fense related as the shift away from nuclear weapons continued. 

Gray, H. R., Ion and Laser Microprobes Applied to the Measurement of Corrosion-Produced Hydrogen on a Microscopic Scale , Corrosion, 28, 47 (1972)... 

The flow patterns for single phase, Newtonian and non-Newtonian liquids in tanks agitated by various types of impeller have been repotted in the literature.1 3 27 38 39) The experimental techniques which have been employed include the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles, and measurement of local velocities by means of Pitot tubes, laser-doppler anemometers, and so on. The salient features of the flow patterns encountered with propellers and disc turbines are shown in Figures 7.9 and 7.10. 

J.L. Brand, A.A. Deckert, and S.M. George, Surface diffusion of hydrogen on sulfur-covered Ru(001) surfaces studied using laser-induced thermal desorption, Surf. Sci. 194, 457-474 (1988). 

It can also be deposited by the hydrogen reduction of the nickel chelate, Ni(C5HFg02)2 at 250°C.P 1 In addition to thermal processing reviewed above, nickel is deposited by laser C VD from the carbonyl with a krypton or a pulsed CO2 laser.P lP l... 

Platinum produced by the decomposition of platinum hexafluoro-2,4-pentadionate, Pt(CF3COCHCOCp3)2 by an argon laser has been reported.The metal can also be obtained from the decomposition oftetrakis-trifluorophosphine, Pt(Pp3)4 at200-300°C in an atmosphere of hydrogen,... 

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