Can stimulated Raman pumping cause large population transfers in isolated molecules?

The Journal of Chemical Physics

Zare

2013

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Using stimulated Raman adiabatic passage (SARP), it is possible, in principle, to transfer all the population in a rovibrational level of an isolated diatomic molecule to an excited rovibrational level. We use an overlapping sequence of pump (532 nm) and dump (683 nm) single-mode laser pulses of unequal fluence to prepare isolated H2 molecules in a molecular beam. In a first series of experiments we were able to transfer more than half the population to an excited rovibrational level [N. Mukherjee, W. R. Dong, J. A. Harrison, and R. N. Zare, J. Chem. Phys. 138(5), 051101-1-051101-4 (2013)]. Since then, we have achieved almost complete transfer (97% ± 7%) of population from the H2 (v = 0, J = 0) ground rovibrational level to the H2 (v = 1, J = 0) excited rovibrational level. An explanation is presented of the SARP process and how these results are obtained.

Section: Introductionmentioning

confidence: 99%

Optical preparation of H2 rovibrational levels with almost complete population transfer

Dong

The Journal of Chemical Physics

Zare

2013

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“…As has been previously described, in order to prevent the coherent return of population, the pump and probe pulses must be separated in time. 13 Because the sweep rate (d∆/dt) is almost entirely determined by the intensity profile of the pump pulse and the two-photon Rabi frequency Ω is determined by the product of the pump and Stokes electric fields, there is an optimum delay for which the adiabatic condition is most easily satisfied. At this delay there simultaneously exist both a moderate sweep rate and a large Rabi frequency over a wide range of initial values of the detuning.…”

Section: Methodsmentioning

confidence: 99%

Preparation of a selected high vibrational energy level of isolated molecules

Perreault

The Journal of Chemical Physics

Zare

2016

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Stark induced adiabatic Raman passage (SARP) allows us to prepare an appreciable concentration of isolated molecules in a specific, high-lying vibrational level. The process has general applicability, and, as a demonstration, we transfer nearly 100 percent of the HD (v = 0, J = 0) in a supersonically expanded molecular beam of HD molecules to HD (v = 4, J = 0). This is achieved with a sequence of partially overlapping nanosecond pump (355 nm) and Stokes (680 nm) single-mode laser pulses of unequal intensities. By comparing our experimental data with our theoretical calculations, we are able to draw two important conclusions: (1) using SARP a large population (>10 molecules per laser pulse) is prepared in the (v = 4, J = 0) level of HD and (2) the polarizability α (≅0.6 × 10 C m V) for the (v = 0, J = 0) to (v = 4, J = 0) Raman overtone transition is only about five times smaller than α for the (v = 0, J = 0) to (v = 1, J = 0) fundamental Raman transition. Moreover, the SARP process selects a specific rotational level in the vibrational manifold and can prepare one or a phased linear combination of magnetic sublevels (M states) within the selected vibrational-rotational level. This capability of preparing selected, highly excited vibrational levels of molecules under collision-free conditions opens new opportunities for fundamental scattering experiments.

“…This is because the homonuclear symmetry forbids infrared excitation, and the Raman pumping is generally weak, requiring large optical intensities that further complicate the optical preparation of a vibrationally excited target state. For one to meet this challenge, a new coherent optical technique called Stark-induced adiabatic Raman passage or SARP − was developed; it allows preparation of a large quantity of H 2 and other molecules in a single rovibrational ( v , j , m ) eigenstate. SARP offers the field-free stereodynamic control by controlling the alignment of the rotational plane or the molecular bond axis with respect to an axis in the laboratory frame.…”

Section: Introductionmentioning

confidence: 99%

Quantum-Controlled Collisions of H₂ Molecules

2023

J. Phys. Chem. A

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The amount of information that can be obtained from a scattering experiment depends upon the precision with which the quantum states are defined in the incoming channel. By precisely defining the incoming states and measuring the outgoing states in a scattering experiment, we set up the boundary condition for experimentally solving the Schrodinger equation. In this Perspective we discuss cold inelastic scattering experiments using the most theoretically tractable H 2 and its isotopologues as the target. We prepare the target in a precisely defined rovibrational (v, j, m) quantum state using a special coherent optical technique called the Stark-induced adiabatic Raman passage (SARP). v and j represent the quantum numbers of the vibrational and rotational energy levels, and m refers to the projection of the rotational angular momentum vector j on a suitable quantization axis in the laboratory frame. Selection of the m quantum numbers defines the alignment of the molecular frame, which is necessary to probe the anisotropic interactions. For us to achieve the collision temperature in the range of a few degrees Kelvin, we co-expand the colliding partners in a mixed supersonic beam that is collimated to define a direction for the collision velocity. When the bond axis is aligned with respect to a well-defined collision velocity, SARP achieves stereodynamic control at the quantum scale. Through various examples of rotationally inelastic cold scattering experiments, we show how SARP coherently controls the dynamics of anisotropic interactions by preparing quantum superpositions of the orientational m states within a single rovibrational (v, j) energy state. A partial wave analysis, which has been developed for the cold scattering experiments, shows dominance of a resonant orbital that leaves its mark in the scattering angular distribution. These highly controlled cold collision experiments at the single partial wave limit allow the most direct comparison with the results of theoretical computations, necessary for accurate modeling of the molecular interaction potential.