Laser induced fluorescence oscillator

Houcine et al. (64) used a non-intrusive laser-induced fluorescence method to study the mechanisms of mixing in a 20 dm CSTR with removable baffles, a conical bottom, a mechanical stirrer, and two incoming liquid jet streams. Under certain conditions, they observed an interaction between the flow induced by the stirrer and the incoming jets, which led to oscillations of the jet stream with a period of several seconds and corresponding switching of the recirculation flow between several metastable macroscopic patterns. These jet feedstream oscillations or intermittencies could strongly influence the kinetics of fast reactions, such as precipitation. The authors used dimensional analysis to demonstrate that the intermittence phenomenon would be less problematic in larger CSTRs. 

Figure 6. Instrumental schematic for vacuum UV photofragmentation-laser induced fluorescence measurement of ammonia SHGC, second harmonic generation crystal SFMC, sum frequency mixing crystal BS, beam splitter BD, beam dump TP, turning prism CL, cylindrical lens R, reflector TD, trigger diode OSC, oscillator cell AMP, amplifier cell BE, beam expander G, grating OC, output coupler M, mirror BC, beam combiner L, lens A, aperture PD, photodiode SC, sample cell RC, reference cell FP, filter pack SAM.PMT, sample cell photomultiplier REF.PMT, reference cell photomultiplier PP, additional photomultiplier port EX, exhaust and CGI, calibration gas inlet to flow line. (Reproduced with permission from reference 15. Copyright 1990 Optical Society of America.)...

Laser-induced fluorescence (LIF) is a preferred method over IR and Raman for detection of compounds in low concentrations due to its higher sensitivity. However, it requires access to relatively low lying excited states with sizeable oscillator strengths and Franck-Condon factors with respect to the ground state. 

Figure 2.11 Vibrational and rotational motion of the I2 molecule. Left potential energy curves of the ground-state X Eg, the excited intermediate Ballou state reached by the pump laser and the final exdted (ion-pair) state fOg of I2 populated by the probe laser. The vibrational (and rotational) motion of the superposition of levels / of I2 in the Ballou state is monitored by the probe laser-induced fluorescence. Right laser-induced fluorescence intensity as a function of the delay time between probe pulse and pump pulse, showing the oscillation of the wave packet for the vibrational (top panel) and rotational (bottom panel) motion. For further details see text. Data adapted from Gruebele et al, Chem. Phys. Lett, 1990, 166 459, with permission of Elsevier...

Fig. 3.3 Sketch of a CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme) apparatus configured for the study of radical-neutral reactions. In this arrangement, radicals are generated by photolysis of a suitable precursor using radiation from a fixed-frequency pulsed laser operating at one of the three wavelengths, 226, 248, or 193 nm, and are detected by laser-induced fluorescence excited by tuneable radiation from a dye laser or a master oscillator parametric oscillator (MOPO) [56]...

Two-photon-induced level crossing [12.30], which relies on the OODR scheme of Raman-type transitions (Fig. 12.7) has been performed with the two neon transitions at = 632.8 nm and 3-39 nm, which have the common upper 3Sj level. A HeNe laser is simultaneously oscillating on both transitions. The Hanle signal S(B) is monitored via the fluorescence from the 2P4 level at A = 667.8 nm. 

Information concerning the interaction potentials of Cs (7S, 5D)-rare gas pairs is obtained by interpreting the temperature dependence of the 6S-7S,5D far wing and satellite profiles. A sensitive laser fluorescence technique is used to obtain the absorption coefficient of the mixture. The collision induced oscillator strength, a rapidly varying function of the interatomic distance in the case of such forbidden transitions, is also deduced. Experimental potentials and oscillator strengths are compared with available calculated values. 

Two femtosecond laser pulses were used in the experiment of FS TR SEP ED. One pulse was used as a pump source to excite the molecule to the electronically excited state, to generate fluorescence. The other, with a specific delay time, was used to perform SEP from the electronic excited states to the ground state. The variation of the decrease in the fluorescence induced by the SEP with delay time reflects vibrational relaxation in the excited states. A homemade regenerative amplified self-mode-locking Ti sapphire femtosecond laser, whose oscillator and amplifier... 

Instead of the active modulator a saturable absorber is put inside the laser resonator, close to one of the end mirrors (Fig. 11.12). The absorbing transition k) - i) takes place between the levels i) and k) with short relaxation times Tj, In order to reach oscillation threshold in spite of the absorption losses the gain of the active medium must be correspondingly high. In case of a pulsed pump source the emission of the active laser medium at a time shortly before threshold is reached, consists of fluorescence photons which are amplified by induced emission. The peak power of... 

Judd (1962) and Ofelt (1962) independently derived expressions for the oscillator strength of induced electric dipole transitions within the f configuration. This was a signal accomplishment. Much of the highly significant theoretical interpretation of the fluorescence process and the prediction of the properties of solid state lanthanide lasers, ch. 35, was made possible by this work. Since their results are similar, and were published simultaneously, the basic theory has become known as the Judd-Ofelt theory. However, Judd s expression, eq. (24.6), was cast in a form that could be directly related to oscillator strengths derived from lanthanide solution spectra, and he was the first to show that the model satisfactorily reproduced the experimental results for Nd (aquo) and... 

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