Laser measurement

The methods and means for ecological diagnostics make rapid strides among all the NDT and TD developing areas. To provide the atmosphere monitoring recently the good results were achieved in the development of surface-acoustics wave sensors (SAW), laser measuring systems, infrared detectors and systems based on other physical principles. 

A final example of laser measurement techniques is measurement of the velocity of fluid flow (79) (see Flow measurement). If a laser beam is directed into a transparent fluid, some of the light may be scattered with a frequency shift zy given by... 

A qualitatively different approach to probing multiple pathways is to interrogate the reaction intermediates directly, while they are following different pathways on the PES, using femtosecond time-resolved pump-probe spectroscopy [19]. In this case, the pump laser initiates the reaction, while the probe laser measures absorption, excites fluorescence, induces ionization, or creates some other observable that selectively probes each reaction pathway. For example, the ion states produced upon photoionization of a neutral species depend on the Franck-Condon overlap between the nuclear configuration of the neutral and the various ion states available. Photoelectron spectroscopy is a sensitive probe of the structural differences between neutrals and cations. If the structure and energetics of the ion states are well determined and sufficiently diverse in... 

Guiraud, P., J. Bertrand, and J. Costes (1991). Laser measurements of local velocity and concentration in a turbulent jet-stirred tubular reactor. Chemical Engineering Science 46, 1289-1297. 

Tunable Diode Laser Measurements of Biomass Kinetics... 

Immediately upon excitation of an IPCT band with a fs laser at 400 nm, transient absorption was observed for both salts in solutions with a peak at about 600 nm, characteristic of 4,4/-bipyridinium radical cations. Figure 20 shows the transient absorption spectra of PV2+(I )2 in methanol solution. A marked increase in the absorbance of the 4,4/-bipyridinium radical cations took place within 1 ps after excitation. 4,4/-Bipyridinium radical cations were thus formed in a fs time scale by the photoinduced electron transfer from a donor I- to an acceptor 4,4/-bipyridinium upon IPCT excitation [48], The time profiles of transient absorption at 600 nm are shown in Fig. 21 for (a) PV2+(I )2 in a film cast from DME and (b) PV2+(TFPB )2 in DME solutions. Both of them showed a very rapid rise in about 0.3 ps, which was almost the same as the time resolution of our fs Ti sapphire laser measurement system with a regenerative amplifier. Similar extremely rapid formation of 4,4/-bipyridinium radical cations was observed for PV2+(I )2 salts in methanol and dimethylsulfoxide solutions upon IPCT excitation, respectively. These results demonstrated that the charge separated 4,4/-bipyridinium radical cations were formed directly upon IPCT excitation because of the nature of IPCT absorption bands (that the electrons correlated with the IPCT band are transferred partially at the ground state and completely at the excited state). Such a situation is very different from usual photochromism which is caused by various changes of chemical bonds mainly via the excited singlet state. No transient absorption was observed for PV2+(I )2... 

The measurements of temperature and species concentrations profiles in premixed, laminar flames play a key role in the development of detailed models of hydrocarbon combustion. Systematic comparisons are given here between a recent laminar methane-air flame model and laser measurements of temperature and species concentrations. These results are obtained by both laser Raman spectroscopy and laser fluorescence. These laser probes provide nonintrusive measurements of combustion species for combustion processes that require high spatial resolution. The measurements reported here demonstrate that the comparison between a model and the measured concentrations of CH, O2,... 

Varghese, P. L. and Hanson, R. K., "Diode Laser Measurements of CO Collision Halfwidths and Fundamental Band Strength at Room Temperature" to be published. 

To help evaluate the quality of the tubes, Quest Integrated has developed a tube inspection system using laser measurement for more accurate determination of tube diameter. The new system is called LOTIS (Laser Optical Tube Inspection System), and it provides rapid reformer tube diameter measurement with very high accuracy. The data from LOTIS can be used to estimate remaining tube life, determine appropriate operating adjustments or identify tubes that need to be replaced82. 

In the last few years, first measurements have been performed determining the length of the attosecond soft X-ray bunches. Paul et al. measured 250 attosecond pulses in a two-color photoionization experiment [5]. Making use of the fact that in a train of soft X-ray bunches the frequency spectrum consists of odd multiples ( harmonics ) of the frequency of the driver laser, they studied the ionization of Ar atoms by simultaneous photo-absorption from the soft X-ray bunch and the fundamental color of the femtosecond laser. Measured... 

Another domain of fs comb accuracy confirmation was provided by comparison of the apparent measured frequency of a HeNe 12-stabilized laser, measured... 

One must be modest" is an appropriate quotation to describe laser spectroscopy of the hydrogen atom. This is a field of modest scientific accomplishments, despite its awesome technical machinery. To illustrate, the first demonstration of laser spectroscopy in hydrogen was made by HANSCH, SHAHIN, and SCHAWLOW in 1972. [2] Now, sixteen years later, the most precise laser measurement of the Lamb shift in the ground state of hydrogen is by the Oxford group and is known to one part in ten thousand. [3] This is just equal to that achieved by LAMB and coworkers thirty-five years ago. [i ] In the meanwhile, radio frequency and other techniques have pushed the measurement of the H(2S) Lamb shift an order of magnitude beyond the accomplishments of laser spectroscopists. [5]... 

Positronium still presents rather formidable theoretical challenges [39], since it is a relativistic two-body system which cannot be approximated by the motion of a particle of reduced mass in a fixed Coulomb potential. In addition, QED calculations must include annihilation terms. First laser measurements of the 1S-2S two-photon transition frequency in positronium [40] give a result about five standard deviation lower than the theoretical predictions, after taking a recalibration of the tellurium reference line into account [41]. On the other hand, as yet uncalculated higher order terms could well account for this discrepancy. 

The experiments discussed at the end of the previous section provided information about the translational excitation of the products of unimolecular fragmentation of energized species formed in association reactions. The distributions of vibrational energy in the products of some reactions of this, and related, types have been determined by chemical laser measurements and by observations of infrared chemiluminescence. Some of these studies were referred to in Section III.C, other reactions have been studied more recently [388-392], In all of these investigations, the product which has been observed is HF or HC1 formed in what is frequently termed a snap-out reaction. These processes require that, almost simultaneously, two bonds break, the HX bond forms, and the order of a bond in the other product is increased. The reverse reaction, a four-centre (bimolecular) one, has a high activation barrier, so in the snap-out process a considerable proportion of the total energy is released after the system passes through the activated state. Thus reaction (120)... 

In laser measurements on hydrogen halides, the system under investigation is itself all, or part, of the active laser medium. Similar experiments have not yet been made on other molecules. However, in related experiments on CO, in the author s laboratory [242,432] and elsewhere [433], a CO cw laser has been used to probe the vibrational distributions in a reaction system outside the optical cavity that may act as an amplifier or absorber of lines from the laser. Time-resolved observations can be made for as long as one chooses after the reaction is initiated. If tunable infrared lasers become readily available this technique is likely to be applied more widely. 

Heuer and Schweehten [15] designed a sampler for installation with a fluidized bed jet mill where the entire classifier product passed through a Sympatec laser measuring device. This system is suitable for use with... 

For example, an Nd YAG laser was used by the Near Earth Asteroid Rendezvous (NEAR) spacecraft in 2000 to map the surface of the asteroid Eros. Light beams sent out by the laser measured with a high degree of accuracy the elevation of various parts of the asteroid, providing one of the best topographical maps of an asteroid surface ever obtained. 

The network of 211 weather stations allows measurement of tens of basic weather parameters, the most important of which include air temperature, atmospheric pressure, air humidity, wind speed and wind direction. Among the other parameters measured are cloud base height (laser-measured), amount of precipitation (rain or snow), visibility, and air temperature near the ground. Measurements are performed in enclosed areas within the weather stations. 

Figure 7. Two laser measurements of the translational energy dependence of the reaction cross section for H + D2 - HD + D. Rectangles experimental results [K. Tsukiyama, B. Katz, and R. Bersohn, J. Chem. Phys. 84, 1934 (1986) and private communication]. Points Classical trajectory computations on the best available ab initio potential energy surface [by N. C. Blais and D. G. Truhlar (triangles) and by I. Schechter (circles)].

Since the rate of stimulated emission can be very much faster than the spontaneous emission rate, the time resolution of chemical laser measurements can be quite high. In a very crude way one might say that the rate of emission under lasing conditions can be deliberately increased by a sufficiently intense stimulating field so as to exceed any other collisional rate in... 

The reacting flow test rig was constructed at the Gas Dynamics and Propulsion Laboratory at the University of Cincinnati. The 3D geometry is shown in Fig. 10.8. For better optical observation and laser measurement, the combustion chamber has an octagonal shape with four flat quartz windows. Four... 

Picosecond laser measurements with trans-stilbene in solution (and even in the gas phase) agree in the respect that the fluorescence decay is single exponential (Table 14). Earlier results assuming a slow and a fast fluorescence decay component [376] have not been confirmed in at least four different laboratories [314, 321-323, 342, 349]. Because of the monoexponential decay, the back reaction 1 p —> 11 has to be much slower than the forward reaction t -. Elowever, the adiabatic formation of t from c indicates that the rate constants of both processes in solution have the same order of magnitude, independent of temperature. The low efficiency, %0.3%, of the p -> t process reflects very rapid p - p decay rather than a low p energy [81]. 

The rates of excimer formation in model compounds for poly(vinylcarbazole) have been determined by ps laser measurements. Two distinct rate constants for excimer formation were measured for the racemic and meso forms of either the vinylnaphthalene dimers or the vinylcarbazole dimers, with k0M of the meso forms larger by about one order of magnitude than DM of the racemic forms. 

Sassenscheid, K. (2001) Infra-red laser measuring technology - new perspectives for process analysis and environmental analysis. GIT Labor-Fachzeitschrift, 45 (9), 962-963. 

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