Adiabatic Passage by Light-Induced Potentials in Molecules (original) (raw)
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Stimulated Raman adiabatic passage in molecules: the effects of background states
We explore theoretically the rovibrational dynamics of stimulated Raman adiabatic passage ͑STIRAP͒ in molecular electronic states including both the rotational and the vibrational degrees of freedom, with the LiH molecule as an example. By using a pure rovibrational state as initial state, we find that, under the condition of two-photon resonance, an efficient rovibrational population transfer can be achieved via STIRAP in molecular electronic states and the desired target state can be selected by adjusting laser-pulse parameters. Besides the interested rovibrational states, however, some unwanted rovibrational states may affect population transfer process, especially while the two-photon detuning is taken into account. By inspecting the evolution process of wave packet, we can easily search these unwanted rovibrational states and study their influences. Moreover, the effect of rotational temperature on the population transfer process is discussed using thermal mixed state as initial state.
Stimulated Raman Adiabatic Passage in a Dense Medium
Advances in Physical Chemistry, 2010
We have considered a coherent population transfer to a higher excited singlet state (S2) of molecules with anomalous fluorescence in molecular assemblies (e.g., a dense medium). A direct excitation to S2 requires light in the UV region. Because of this, the transition is conveniently realized by a two-step (two-photon) process: S0→S1→S2, where transitions S0→S1 and S1→S2 correspond to the optical region. We have shown that efficient stimulated Raman adiabatic passage (STIRAP) in the ladder configuration can be realized in this case, using suitably chirped pulses, to compensate a change of the two-photon transition frequency in time, induced by the pulses themselves, due to near dipole-dipole interactions. We have provided a reduced state formulation of the optical control process. Chirping the “pump” pulse that excites transition S0→S1 is nonequivalent to chirping the “Stokes” pulse that excites transition S1→S2, with respect to the population of the intermediate state (S1) in the p...
The Journal of Chemical Physics, 2013
By using Stark-induced adiabatic Raman passage (SARP) with partially overlapping nanosecond pump (532 nm) and Stokes (683 nm) laser pulses, 73% ± 6% of the initial ground vibrational state population of H 2 (v = 0, J = 0) is transferred to the single vibrationally excited eigenstate (v = 1, J = 0). In contrast to other Stark chirped Raman adiabatic passage techniques, SARP transfers population from the initial ground state to a vibrationally excited target state of the ground electronic surface without using an intermediate vibronic resonance within an upper electronic state. Parallel linearly polarized, co-propagating pump and Stokes laser pulses of respective durations 6 ns and 4.5 ns, are combined with a relative delay of ∼4 ns before orthogonally intersecting the molecular beam of H 2. The pump and Stokes laser pulses have fluences of ∼10 J/mm 2 and ∼1 J/mm 2 , respectively. The intense pump pulse generates the necessary sweeping of the Raman resonance frequency by ac (second-order) Stark shifting the rovibrational levels. As the frequency of the v = 0 → v = 1 Raman transition is swept through resonance in the presence of the strong pump and the weaker delayed Stokes pulses, the population of (v = 0, J = 0) is coherently transferred via an adiabatic passage to (v = 1, J = 0). A quantitative measure of the population transferred to the target state is obtained from the depletion of the ground-state population using 2 + 1 resonance enhanced multiphoton ionization (REMPI) in a time-of-flight mass spectrometer. The depletion is measured by comparing the REMPI signal of (v = 0, J = 0) at Raman resonance with that obtained when the Stokes pulse is detuned from the Stark-shifted Raman resonance. No depletion is observed with either the pump or the Stokes pulses alone, confirming that the measured depletion is indeed caused by the SARPinduced population transfer from the ground to the target state and not by the loss of molecules from photoionization or photodissociation. The two-photon resonant UV pulse used for REMPI detection is delayed by 20 ns with respect to the pump pulse to avoid the ac Stark shift originating from the pump and Stokes laser pulses. This experiment demonstrates the feasibility of preparing a large ensemble of isolated molecules in a preselected single quantum state without requiring an intermediate vibronic resonance.
Adiabatic Population Transfer Based on a Double Stimulated Raman Adiabatic Passage
2014
Stimulated Raman adiabatic passage (STIRAP) is an adiabatic population-transfer technique that uses two coherent laser pulses in counter-intuitive order, namely, pump and stoke, to achieve complete transfer between two quantum states. Here, we propose a double STIRAP scheme whereby the electronic levels of a four-level atom are coupled by three laser fields forming two pairs of stoke and pump pulses. We derive the optical Bloch equations through the master equation for studying the population dynamics. We show that manipulating the time between two STIRAP sequences provides the state transfer near unity. In particular, we show that there occurs a certain maximum transfer efficiency that can be achieved in the double STIRAP process.
Stark-induced adiabatic Raman passage for preparing polarized molecules
The Journal of Chemical Physics, 2011
We propose a method based on Stark-induced adiabatic Raman passage (SARP) for preparing vibrationally excited molecules with known orientation and alignment for future dynamical stereochemistry studies. This method utilizes the (J, M)-state dependent dynamic Stark shifts of rovibrational levels induced by delayed but overlapping pump and Stokes pulses of unequal intensities. Under collision-free conditions, our calculations show that we can achieve complete population transfer to an excited vibrational level (v > 0) of the H 2 molecule in its ground electronic state. Specifically, the H 2 (v = 1, J = 2, M = 0) level can be prepared with complete population transfer from the (v = 0, J = 0, M = 0) level using the S(0) branch of the Raman transition with visible pump and Stoke laser pulses, each polarized parallel to theẑ axis (uniaxial π − π Raman pumping). Similarly, H 2 (v = 1, J = 2, M = ±2) can be prepared using SARP with a left circularly polarized pump and a right circularly (or vice versa) polarized Stokes wave propagating along theẑ axis (σ ± − σ ∓ Raman pumping). This technique requires phase coherent nanosecond pulses with unequal intensity between the pump and the Stokes pulses, one being four or more times greater than the other. A peak intensity of ∼16 GW/cm 2 for the stronger pulse is required to generate the desirable sweep of the Raman resonance frequency. These conditions may be fulfilled using red and green laser pulses with the duration of a few nanoseconds and optical energies of ∼12 and 60 mJ within a focused beam of diameter ∼0.25 mm. Additionally, complete population transfer to the v = 4 vibrational level is predicted to be possible using SARP with a 355-nm pump and a near infrared Stokes laser with accessible pulse energies.
The Journal of Chemical Physics, 2001
We investigate two-photon, selective excitation of diatomic molecules with intense, ultrafast laser pulses. The method involves transfer of a vibrational population between two electronic states by shaping of light-induced potentials ͑LIPs͒. Creation and control of the LIPs is accomplished by choosing pairs of transform-limited pulses with proper frequency detunings and time delays. Depending on the sequence of pulses ͑intuitive or counter-intuitive͒ and on the sign of the detuning ͑below or above the first transition͒ four schemes are possible for population transfer by LIP shaping. We develop a simple analytic model to predict the optimal laser pulses, and to model the adiabatic dynamics in the different schemes. Based on a harmonic, three-state model of the sodium dimer we demonstrate numerically that all four schemes can lead to efficient, selective population transfer. A careful analysis of the underlying physical mechanisms reveals the varying roles played by the adiabatic and diabatic crossings of the LIPs. The detailed mechanisms influence the robustness and experimental applicability of the schemes.
The European Physical Journal D, 1998
We develop an adiabatic two-mode Floquet theory to analyse multiphoton coherent population transfer in N-level systems by two delayed laser pulses, which is a generalization of the three-state stimulated Raman adiabatic passage (STIRAP). The main point is that, under conditions of non-crossing and adiabaticity, the outcome and feasibility of a STIRAP process can be determined by the analysis of two features: (i) the lifting of degeneracy of dressed states at the beginning and at the end of the laser pulses, and (ii) the connectivity of these degeneracy-lifted branches in the quasienergy diagram. Both features can be determined by stationnary perturbation theory in the Floquet representation. As an illustration, we study the corrections to the RWA of the (1+1) STIRAP in strong fields and for large detunings. We analyse the possible breakdown of connectivity. In strong fields, the complete transfer is achieved, but the intermediate state, unpopulated within the RWA, can become populated during the process. In the (2+1) STIRAP, we show a residual degeneracy in a four-level system, that can be lifted by additional Stark shifts. The complete transfer is achieved under conditions of connectivity.