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Mon, 02 Jul 2001 00:00:00 +0200Mon, 02 Jul 2001 00:00:00 +0200Coherent population transfer beyond the adiabatic limit: generalized matched pulses and higher-order trapping states
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1301
Abstract: We show that the physical mechanism of population transfer in a 3-level system with a closed loop of coherent couplings (loop-STIRAP) is not equivalent to an adiabatic rotation of the dark-state of the Hamiltonian but coresponds to a rotation of a higher-order trapping state in a generalized adiabatic basis. The concept of generalized adiabatic basis sets is used as a constructive toolto design pulse sequences for stimulated Raman adiabatic passage (STIRAP) which give maximum population transfer also under conditions when the usual condition of adiabaticty is only poorly fulfilled. Under certain conditions for the pulses (generalized matched pulses) there exists a higher-order trapping state, which is an exact constant of motion and analytic solutions for the atomic dynamics can be derived.M. Fleischhauer; R. Unanyan; B.W. Shore; K. Bergmannpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1301Mon, 02 Jul 2001 00:00:00 +0200Measuring a coherent superposition
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1212
Abstract: We propose a simple method for measuring the populations and the relative phase in a coherent superposition of two atomic states. The method is based on coupling the two states to a third common (excited) state by means of two laser pulses, and measuring the total fluorescence from the third state for several choices of the excitation pulses.K. Bergmann; N.V. Vitanov; B.W. Shore; R.G. Unanyanpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1212Wed, 09 May 2001 00:00:00 +0200Photoionization Suppression by Continuum Coherence: Experiment and Theory
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1213
Abstract: We present experimental and theoretical results of a detailed study of laser-induced continuum structures (LICS) in the photoionization continuum of helium out of the metastable state 2s^1 S_0. The continuum dressing with a 1064 nm laser, couples the same region of the continuum to the 4s^1 S_0 state. The experimental data, presented for a range of intensities, show pronounced ionization suppression (by asmuch as 70% with respect to the far-from-resonance value) as well as enhancement, in a Beutler-Fano resonance profile. This ionization suppression is a clear indication of population trapping mediated by coupling to a contiuum. We present experimental results demonstrating the effect of pulse delay upon the LICS, and for the behavior of LICS for both weak and strong probe pulses. Simulations based upon numerical solution of the SchrÃ¶dinger equation model the experimental results. The atomic parameters (Rabi frequencies and Stark shifts) are calculated using a simple model-potential method for the computation of the needed wavefunctions. The simulations of the LICS profiles are in excellent agreement with experiment. We also present an analytic formulation of pulsed LICS. We show that in the case of a probe pulse shorter than the dressing one the LICS profile is the convolution of the power spectra of the probe pulse with the usual Fano profile of stationary LICS. We discuss some consequences of deviation from steady-state theory.L.P. Yatsenko; T. Halfmann; B.W. Shore; K. Bergmannpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1213Wed, 09 May 2001 00:00:00 +0200