Pulse Fourier-Transform Optical Spectroscopy

Abstract

are 12% and 5%, respectively. Some of the discrepancy can be understood to be due to the finite-range effect 9 ; the difference may well be within the range expected for shell effects in highly deformed nuclei. 10 The relative importance of multiple-chance fission contributions to the total fission excitation function calculated with parameter set (c) is exhibited in Fig. 2. The principal multiple-chance fission components are displayed. In the threshold region, multiple-chance fission is dominant; and at 169 MeV, the contributions due to firstthrough fourth-chance fission are 2.5, 1.4, 3.8, and 2.5 mb, respectively. The relative importance of multiple-chance fission decreases with increasing excitation energy, although at 337 MeV the multiple-chance contribution is still 33% of the total.To summarize: (1) It is necessary to fit fission and evaporation-residue excitation functions simultaneously over a broad excitation-energy range and to use experimental Z crtt values in order to obtain unambiguous model parameters.(2) The assumption that only first-chance fission need be considered in such analyses is a poor one for the parametrization considered herein. (3) A reduction in the liquid-drop barriers on the order of 35-45% is necessary to reproduce the experimental excitation functions in the mass-150 region.The optical analog of pulse Fourier-trans form NMR spectroscopy is demonstrated. Doppler-free infrared spectra are obtained for a set of closely spaced 13 CH 3 F transitions at 9.66 jum from two-pulse echo and free-induction decay transients. The effects of elastic or inelastic collisions on the decay rate are obtained for each transition, and the long-range force laws are deduced from the dependence of the scattering cross section on molecular velocity.The method of Fourier transforming transient phenomena from the time to the frequency domain has proven to be an extremely versatile technique in pulsed nuclear-magnetic-resonance (NMR) spectroscopy. 1 With it, ultrahigh-resolution NMR spectroscopy can be performed quickly and with high sensitivity in a set of densely spaced lines. 2 Since the NMR signals display coherent transient behavior, dynamic information about nuclear spin interactions can be derived in a selective manner for each transition as well. 3 This Letter reports an initial demonstration of this Fourier-transform technique in the optical region. By employing suitable coherent optical transient effects in a sample of 13 CH 3 F, we are able to resolve Doppler-free spectra in a set of closely spaced lines (Fig. 1). The decay characteristics for each transition are obtained also and 275

Infrared HCN Lineshapes as a Test of Galatry and Speed-Dependent Voigt Profiles

“…From an experimental point of view, reported experiments were performed in the linear interaction regime, which leads to a global response of the sample and makes a detailed analysis intricate. So the interest of experiments in the nonlinear regime, such as saturated absorption or photon echoes experiments, must be emphasized for the analysis of velocity-changing collisions (68,69) or of the speed dependence of relaxation (19)(20)(21)70).…”

“…However, such a distinction seems rather artificial since molecular diffusion and speed dependence of relaxation both result from collision processes, whatever the pressure is. Particularly, whereas the Dicke effect actually becomes negligible in the collisional regime (6), effects of the speed dependence of relaxation, which have been observed for a long time in nonlinear spectroscopy (19)(20)(21), show up even in the Doppler regime (22,23). It would thus be more satisfying to have a unique lineshape model valid for the whole pressure range explored.…”

Self and Polar Foreign Gas Line Broadening and Frequency Shifting of CH3F: Effect of the Speed Dependence Observed by Millimeter-Wave Coherent Transients

“…the dependence of relaxation with the temperature and with Finally, it is interesting to note that a better discrimina-molecular speeds, it must be pointed out that a too crude tion between these two processes can be expected from model of the interaction potential can lead to contradictory infrared experiments using a double resonance technique results, particularly in the case of molecular systems involv-( 35 ) or a time-resolved technique ( 36 ) . Among these ve-ing many collisional relaxation channels: a satisfactory interlocity selective experiments, the comparison of two-pulse pretation then requires a realistic description of the potential and stimulated photon echo experiments seems quite and of the molecular level manifold involved.…”

Collision-induced photon echo at the transition0↔1in ytterbium vapor: Direct proof of depolarizing collision anisotropy

“…Corresponding cross sections and collision decay rates were calculated on the basis of the isotropic model, taking into account the transitions between quantum states of molecules caused by collisions [25,26]. A simple model of the interaction potential V ∝ 1/r n with n 3 (here r is the distance between active atom and buffer particle) used in [27] (see also references) was presented in order to explain the results concerning velocity dependence of collision decay rate (v) measured by photon echo generated in 13 CH 3 F gas via level Stark switching in the presence of saturating cw laser radiation. The traditional method of photon-echo generation was used in [28] to study (v) dependence in gas SF 6 and in its mixture with Kr.…”