H2O laser

Fig. 1.48 Laser magnetic resonance spectroscopy (a) level diagram (b) experimental set-up with an intracavity sample A and B are the laser resonator mirrors (c) LMR spectrum of CH radicals, superimposed by some OH-lines, measured in a low-pressure oxygen-acetylene flame with an H2O laser [142]...

Starting from microwave frequencies which can be readily compared with the frequency standard, a chain of frequencies can be built up which uses, for example, the HCN laser, the H2O laser, the CO2 laser, and the He-Ne laser, and their harmonics and which has been extended up to 197 THz (1.52 ym). Recently even optical frequencies in the visible range have been directly measured by this synthesis technique. Figure 6.36 shows such a laser frequency synthesis chain as used by EVENSON et al. [6.34]. 

In choosing fhe examples of lasers discussed in Sections 9.2.1 to 9.2.10 many have been left ouf. These include fhe CO, H2O, HCN, colour cenfre, and chemical lasers, all operating in fhe infrared region, and fhe green copper vapour laser. The examples fhaf we have looked af in some defail serve to show how disparate and arbifrary fhe materials seem to be. For example, fhe facf fhaf Ne atoms lase in a helium-neon laser does nof mean fhaf Ar, Kr and Xe will lase also - fhey do nof. Nor is if fhe case fhaf because CO2 lases, fhe chemically similar CS2 will lase also. 

Figure 7. Two-dimensional (2D) H2O system in the laser field, (a)excited and (b) ground adiabatic potentials. Filled circles nonadiabatic tunneling-type region. Open circles LZ-type region. Taken from Ref. [19].

Numerical examples are shown in Figs. 7-9. The model system used is a 2D model of H2O in a continuous wave (CW) laser field of wavelength 515nm and intensity lO W/cm. The ground electronic state X and the first excited state A are considered. The bending and rotational motions are neglected for... 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

Figures 6a-c report the effect of H2O adsorption on Ti(IV) sites on the Raman features of TS-1 using three different excitation sources. As far as the asymmetric modes of the [Ti(OSi)4] units are concerned, we observed a blue shift of the 960 cm band whichever laser was used in the experiment [48,52,64]. More interesting are the consequences that water adsorption has on the to-...

MFEs on the dynamics of the radical pair in CtoN" clusters (C oN " ) -MePH system were examined in TH F-H2O (2 1) mixed solvent. M FEs on the decay profiles of the transient absorption at 5 20 nm due to the phenothiazine cation radical (P H " ) are shown in Eigure 15.9b. The decay was retarded in the presence of the magnetic field. In addition, the absorbance at 10 (is after laser excitation increased with increasing magnetic field. The result indicated that the yield of the escaped PH increased with the increase in magnetic field. Therefore, the MFEs on the decay profile were clearly observed. 

Fig. 9. The translational energy distributions of H2O photodissociation at 121 nm obtained with photolysis laser polarization parallel to the detection direction, (a) The upper trace was acquired experimentally, (b) The lower trace is the simulated distribution.

Similar investigations of pressure broadening effects in H2O were accomplished with the HCN laser by Bradley et al. 98),... 

An interesting method for generation of a broad wavelength continuum with a time duration of some picoseconds has been deseribed by Busch et al. I61e) By focussing the intense mode locked laser beam from a frequency-doubled neodynium laser into various liquids (H2O, P2O, etc.) a light continuum can be generated which spans several thousand wave numbers and yet has a picosecond pulse duration. This enables absorption spectroscopy measurements to be made in the picosecond time scale. 

Several investigations concerned with the identification of these lines succeeded, for instance, in the case of H2O, in elucidating the rotational spectrum in excited vibrational states 356). Through comparison of wavelengths and intensities of many lines in H2O , H2 0 and DjO isotopic effects could be studied in these excited vibrational levels 357,358) Perturbations of rotational levels by Coriolis resonance which mixes different levels could be cleared up through the assignment and wavelength measurement of some DCN and HCN laser lines 359). 

Baer, D. S., M. E. Newfield, N. Gopaul, and R. K. Hanson. 1994. Mnltiplexed diode laser sensor system for simultaneous H2O, O2 and temperatnre measnrements. Optic Letters 19(22) 1900-2. 

An application for multiplexed diode-laser sensors with a potentially large impact is for measurements of important parameters at several locations in a gas turbine combustion system. In this example, illustrated schematically in Fig. 24.1, the multiplexed diode lasers are applied for simultaneous absorption measurements in the inlet, combustion, afterburner, and exhaust regions. For example, measurements of O2 mass flux at the inlet may be determined at the inlet from Doppler-shifted O2 absorption lineshapes near 760 nm. Measurements of gas temperature and H2O concentrations in the combustion and afterburner regions may be determined from H2O lineshape measurements near 1.4 pm. Finally, measurements of velocity, temperature, and species concentrations (e.g., CO, CO2, unburned hydrocarbons) may be recorded in the exhaust for the determination of momentum flux (component of thrust) and combustor emissions. 

Figure 24.2 Schematic diagram of the setup used to measure and control H2O concentration and gas temperature in the combustion region (in situ) of a forced 5-kilowatt combustor at Stanford University 1 — steel duct 2 — quartz duct 3 — A1 duct 4 — multiplexed beam 5 — tunable diode lasers 6 — data acquisition and control computer 7 — control signals 8 — primary air driver Aair sin(27r/of) 9 — fuel drivers Afuei sin(27r/of-f dfuei) 10 — demultiplexing box 11 — Si detector (ND filter) and 12 — laser beam...

Figure 24.3 shows typical single-sweep (raw data) measurements of spectral absorption coefficients obtained simultaneously by tuning two diode lasers independently at 10-kilohertz rates across H2O transitions near 1343 and 1392 nm over a 5-centimeter path through the combustion region x/d = 2) of the forced combustor (jet diameter d = 2.1 cm, 4> = 0.75). The product of the spectral absorption coefficient at frequency v ki, cm ) and path length L, cm) is given by ki,L = ln(/o//)j/, where / and Iq are the transmitted and... 

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