Laser saturation

In conclusion, we have presented three independent experimental results which can be explained on the basis of equilibrated collisional ionization using a laser-saturated level and electrical neutrality of the probed volume. 

The kinetics and mechanisms of radical reactions important in combustion chemistry are best studied under conditions in which single reactions can be isolated rather than in flames where there are multiple pathways for formation and disappearance of the radicals. Reactions of C2 are of particular importance since recent laser saturation measurements in our laboratory (1) have shown that C2 a3IIu is present in oxyacetylene flames at concentrations on the order of 1016 molecules/cm3 (approximately 0.1 torr). Although concentrations of ground state C2 in flames are unknown and cannot be measured by the same technique due to spectroscopic constraints, we expect that C2 X3 g populations are at least comparable. Because of these relatively large concentrations the reactions of both species are of considerable importance in combustion chemistry. However, until recently very little was known about these reactions due to the difficulty of producing a clean source of C2 radicals. 

Laser induced fluorescence is particularly well suited to combustion chemistry, as a sensitive "in-situ" probe for free radicals in flames or under more controlled conditions in laboratory flash photolysis, discharge flow tube, or shock tube experiments. Using laser-saturation fluorescence previous studies from this laboratory (J ) have shown that C2(a3n ) is present in high concentrations in the hot region of an oxy-acetylene flame. C2(a-,n and X1 ) reacts with 0 .(2,3 4) One of the products of this reaction (and/or the reaction of C2H+02) is CC0.(2) In the present study, we report C20()rn.-f, i 7 fluorescence excitation spectra, A"3 , lifetimes and quenching rate constants, and... 

This Doppler width can be avoided by typical sub-Doppler laser spectroscopy techniques. Laser saturation spectroscopy with a resolution close to the natural line width was used for a test of Special Relativity at the ESR. For such sub-Doppler resolution one must also take into account the small additional broadening and shift arising from the angle 0 between laser beam and ion beam in the Doppler formula. At an interaction length of 10 meters and more, angles are easily controlled to be better than 1 mrad. This limits a possible shift, which enters by... 

T. W. Hansch, I. S. Shahin, and A. L. Schawlow, Optical Resolution of the Lamb Shift in Atomic Hydrogen by Laser Saturation Spectroscopy, Nature Physical Science 235, 63-65 (1972). 

T. W. Hansch, M. H. Nayfeh, S. A. Lee, S. M. Curry, and I. S. Shahin, Precision Measurement of the Rydberg Constant by Laser Saturation Spectroscopy of the Bahner a Line in Hydrogen and Deuterium, Physical Review Letters 32, 1336-1340 (1974). 

Picosecond absorption spectroscopy has been employed to follow the time-dependence of the optical absorption during the formation of e, while pulsed-laser saturation spectroscopy has been used to examine the... 

Our present experimental arrangement for kinetic laser saturation spectroscopy with a g-switched ruby laser has been described in detail previously where it has been shown that the amplitude and temporal profile of the probe laser pulses contain the picosecond time history of the /i-level... 

Laser hole-burning experiments in the nanosecond time domain can reveal the picosecond time history of the relaxation times in an n-level system of the molecule if those relaxation times are fast (picosecond) compared to the duration of the laser saturating pulse (nanosecond). Under these circumstances, the levels of the system can be treated as photostationary states and the kinetic equations solved exphcitly for the rate constant between any two specified levels. This leisurely approach to picosecond phenomena is equally valid in the picosecond time domain. 

Fig. 12. Schematic for laser saturation spectroscopy (LSS), showing depletion and recovery in a two-level system. Oscilloscope traces show four transmitted laser pulses at (a) low and...

During high intensity laser saturation of e in alcohols, the experimental details of which are outlined in Section II and elsewhere, we observed... 

X ftactional loss of absorbance following laser saturation at, A2 quoted to 0.05. 

Similar dramatic effects of selective solvation have been also seen in the laser-induced electron transfer (LIFT) processes first discussed in Section V. More recent hole-burning experiments employing a Nd YAG laser indicate that laser saturation at 330 nm also produces a significant, and... 

Fig. Amplification of ultrashort light pulses through a chain of amplifier dye cells G1-G4, pumped by a frequency-doubled pulsed Nd YAG laser. Saturable absorbers SA1-SA3 are placed e ween e amp i er cells in order to prevent feedback by reflection and to suppress amplified spontaneous emission...

J.L. Hall, The Line Shape Problem in Laser-Saturated Molecular Absorption (Gordon Breach, New York, 1969)... 

H.G.Weber Anomolous laser saturation resonances in N0 , Z.Phys.D-Atoms... 

J. Hall The line shape problem in laser saturated molecular absorptions . In Lecture Notes in Theor. Phys., Vol 12A, ed. by K. Mahanthappa, W. Brittin (Gordon and Breach, New York 1971)... 

Chiang et al. measured the nuclear hyperfine splittings in the excited D2 state of Lap3 Pr " with the above-mentioned photon echo technique, utilizing two independently triggered nitrogen-laser-pumped dye lasers. They found agreement with the results of Erickson based on laser saturation measurements. ... 

T. W. H nsch, M.H. Nayfeh, S.A. Lee, S.M. Curry, I.S. Shahin Precision measurement of the Rydberg constant by laser saturation spectroscopy of the Balmer-a line in hydrogen and deuterium. Phys. Rev. Lett. 32, 1336 (1974)... 

However, when the frequency is coincident with the center frequency of the Doppler profile, the weak probe wave interacts with molecules whose absorption has already been reduced by the strong counterrunning wave. Consequently, the absorption of the probe wave has a resonant minimum equal in width to the homogeneous width and centered exactly on the Doppler-broadened absorption line. This method has been demonstrated in experiments using a CO2 laser operating at 10/um and SFe molecules (Basov et al. 1969), and now it is universally accepted in laser saturation spectroscopy. 

Barger, R. L., and Hall, J. L. (1969). Pressure shift and pressure broadening of methane line at 3.39 pm studied by laser-saturated molecular absorption. Physical Review Letters, 22, 4—8. 

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