Laser induced pressure pulse

LBR low birefringence LIPP laser-induced pressure pulse... 

Bias-induced reverse piezoelectric response Broadband dielectric spectroscopy (BDS) Dielectric permittivity spectrum Dielectric resonance spectroscopy Elastic modulus Ferroelectrets Electrical breakdown Acoustic method Characterization Dynamic coefficient Interferometric method Pressure and frequency dependence of piezoelectric coefficient Profilometer Quasistatic piezoelectric coefficient Stress-strain curves Thermal stability of piezoelectricity Ferroelectric hysteresis Impedance spectroscopy Laser-induced pressure pulse Layer-structure model of ferroelectret Low-field dielectric spectroscopy Nonlinear dielectric spectroscopy Piezoelectrically generated pressure step technique (PPS) Pyroelectric current spectrum Pyroelectric microscopy Pyroelectricity Quasistatic method Scale transform method Scanning pyroelectric microscopy (SPEM) Thermal step teehnique Thermal wave technique Thermal-pulse method Weibull distribution... 

Instead of temperature fields, one can use pressure discontinuities in order to probe charge or polarization distributions in dielectrics. According to the pressure excitation method, one can distinguish three basic configurations (a) the LIPP (laser-induced pressure pulse. Fig. 21) (Sessler et al. 1981) or PWP (pressure wave propagation) technique (Alquie et al. 1981), (b) the piezoelectrically generated pressure step technique (PPS, cf. Fig. 22) (Eisenmenger and Haardt 1982), and (c) the pulsed electroacoustic method (PEA, cf Fig. 23) (Takada et al. 1987). 

FVgura 21 Setup for laser-induced pressure pulse method for charge measuremesi (367). 

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... 

Since enthalpy changes can be obtained directly from measurement of heat absorption at constant pressure, even small values of AH for chemical and biochemical reactions can be measured using a micro-calorimeter.1112 Using the technique of pulsed acoustic calorimetry, changes during biochemical processes can be followed on a timescale of fractions of a millisecond. An example is the laser-induced dissociation of a carbon monoxide-myoglobin complex.13... 

The most commonly used method is the direct measurement of a decay rate by pulsed excitation and time resolved detection. The most straightforward example of this technique is laser induced fluorescence applied to alkali Rydberg atoms. Alkali atoms are typically contained in a glass cell, which also holds a known pressure of perturber gas. The alkali atoms are excited to the Rydberg state at time t = 0 and the time resolved fluorescence from the Rydberg atoms is detected... 

We have employed a pulsed laser photolysis - pulsed laser induced fluorescence technique to carry out direct, real time studies of OH reactions with DMS and DMS-dfc in N2, air, and O2 buffer gases. Both temperature and pressure dependencies have been investigated. We find that the observed rate constant (kQbs = d[0H]/[0H] [DMS]dt) depends on the O2 concentration. Our results are consistent with a mechanism which includes an abstraction route, a reversible addition route, and an adduct + O2 reaction which competes with adduct decomposition under atmospheric conditions. 

Gilles and coworkers [37], via pulsed laser photolysis followed by laser induced fluorescence, found the temperature-dependent rate constant for the OH reaction at 50 torr pressure to be 6.6 x cm molecule s for... 

The CO2 laser-induced multiphoton decomposition of silanes, known to be a really homogeneous reaction, was utilized for the chemical vapour deposition of fluorine containing SiC films from the parent (fluoromethyl)silanes [25, 26]. In contrast to work with H3CS1H3, irradiation of (fluoromethyl)silanes with a single unfocused CO2 laser pulse at fluence of S 0.9 Jcm" tuned to absorption bands of either the SiH bending or the CF stretching vibrations results in an explosive reaction. This is accompanied by an intense chemoluminescence when the sample pressure exceeds a certain limit in the range of 0.1-6.7 kPa (Fig. 1). 

A reeent re-evaluation of the rate coefficient and the branching ratio has been made by Williams et al. (2001) using the pulsed laser photolysis-pulsed laser induced fluorescence (PLP-PLIF) teehnique. The effective rate coefficient for the reaction of OH -1- DMS and OH + DMS-db was determined as a function of O2 partial pressure at 600 Torr total pressure in N2/O2 mixtures the temperature was 240 K for DMS and 240, 261, and 298 K for DMS-db. This new work shows that at low temperatures the currently recommended expression underestimates both the effective rate coefficient for die reaction and also the branching ratio between addition and abstraction. For example, at 261 K a branching ratio of 3.6 was obtained as opposed to a value of 2.8 based on the work of Hynes et al. (1986). At 240 K the discrepancy increases between a measured value of 7.8 and a value of 3.9 using the extrapolated values from the 1986 work of Hynes et al. (the branching ratio is defined here as (kobs-kia)/kia). In addition, at 240 K the expression for Us in 1 atm air based on the work of Hynes et al. (1986) predicts a value which is a factor of 2 lower then the value measured at... 

We have developed a new technique of laser pyrolysis/laser fluorescence, or LP/LF (J ), designed to furnish direct measurement of rate constants of reactions involving free radicals at elevated temperatures (800-1400K). A pulsed CO2 laser is used to heat a sample containing a precursor that pyrolyzes to form radicals. These radicals are then detected using laser-induced fluorescence (LIF). The measurement of the radical removal rates in the presence of added reactant then yields the rate constant for the selected conditions of temperature (T) and pressure (P). 

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