Advances in Multi-Photon Processes and Spectroscopy

The following sections are included:

• PREFACE

• Contents

The following sections are included:

• Introduction

• Quantum Control of Nuclear Dynamics
  • Time-Dependent Schrödinger Equation for Nuclear Wave Packets
    • Born-Oppenheimer (BO) Hamiltonian
    • Time-Propagation of Nuclear Wave Packets
  • Overview of Optical Control by Laser Pulses
    • Two-Electronic-State Model
    • One-Electronic-State Model

• Pulse Design by Optimal Control Theory
  • Global Control Method
    • Wave Function Formalism
    • Density Matrix Formalism
    • Relation between the Schrödinger Formalism and the Density Matrix Formalism
    • Calculation Algorithms
    • Perturbative Treatments
    • Other Optimal Control Methods
  • Local Control Method

• Preliminary Results Using the Local Control Method
  • Population Control
    • Population Inversion of a Two-Level System
    • Population Inversion of a Three-level System
  • Wave Packet Control
    • Displaced Harmonic Oscillator Model
    • Displaced Morse Oscillator Model

• Application of the Local Control Method to Photochemical Reactions
  • Control of Photo-isomerization
  • Quantum Control of NaI Predissociation
    • Wave Packet-Shaping Scheme
    • Pump-Dump Control Scheme

• Application of the Optimal (Global) Method to the Control of Intramolecular Vibrational-Energy Redistribution (IVR) Processes

• Concluding Remarks

• Acknowledgment

• References

Coherent control—the study of possible control on the future of any coherent light-matter interaction—has developed into an independent branch of science over the last part of the twentieth century. Theoretical understanding of the quantum interferences that lead to energy randomization and experimental developments in ultrafast laser spectroscopy has been the key to the success of coherent control. While the theoretical predictions on control of reaction channels or energy randomization processes are still more dramatic than the experimental demonstrations, the gap between the two has consistently reduced over the recent years with realistic theoretical models and technological developments. Experimental demonstrations of arbitrary optical pulse shaping have truly made some of the previously impracticable theoretical predictions possible to implement. Starting with the simple laser modulation schemes to provide proof-of-the-principle demonstrations, feedback loop pulse shaping systems have been developed that can actively manipulate ionization channels. This review attempts to capture the overall impact of this fast developing area into different fields of science by covering as many wide applications and developments possible both experimentally and theoretically.

We review a time-dependent two-pulse laser scheme for controlling where nuclei and electrons are going in unimolecular reactions. We consider specifically the objectives of selective bond-breaking in polyatomic molecules and selective electron transfer associated with bond-breaking.

The scheme has a close formal correspondence to pump-probe spectroscopy. Furthermore, in the control scheme for nuclear motion vibration modes are pumped via infrared multiphoton excitation.

The following sections are included:

• Introduction

• The Two-Form Two-State Model of Push-Pull Molecules
  • Presentation of the 2F2S model
  • Static polarizabilities in the 2F2S model
  • Parameters of the 2F2S model : experimental determination

• Two-Form Two-State Guidelines for the Molecular Engineering of δα(0), β(0) or γ(0)
  • Strategy I: optimization of MIX
  • Strategy II: enhancement of the maximum magnitudes
  • Combination of strategies I and II

• Molecular Engineering of β(0): Examples
  • Experimental determinations
  • Strategy I : optimization of MIX and effect on β_max
  • Strategy II : enhancement of β_max and effect on MIX

• Towards Efficient Materials for Photorefractive Applications
  • The prototype push-pull chromophores in PRM
  • The linear, PEO and KEO susceptibility tensors
  • The mechanisms generating the PR effect in PRM
    • The conventional PR contributions in a high-T_g PRM
    • The conventional and non-conventional PR contributions in a low-T_g PRM
  • Figures of merit of push-pull chromophores in PRM
    • General expressions of the figures of merit
    • 2F2S expressions of the figures of merit
  • Two-form two-state guidelines for the molecular engineering of FOM(OB), FOM(PEO) and FOM(KEO)
  • Examples of push-pull polyenes for PRM
    • Molecular engineering of FOM(OB)
    • Molecular engineering of FOM(PEO)
    • Molecular engineering of FOM(KEO)
    • Molecular engineering of FOM_L(PR) and FOM_H(PR)

• Conclusion

• References

In the present work, we review the theoretical descriptions of sum-frequency generation and pumped sum-frequency generation applied to the studies of the dynamical processes taking place in adsorbed molecular systems at surfaces or interfaces. Both steady-state and pulsed regimes are treated on the same footing. From the spectral decomposition of the evolution Liouvillians and the formal solution of the multiple time integrals, any process can in, principle, be described. Here, we emphasize on the more frequently encountered case of infrared-visible sum-frequency spectroscopy. The case of resonant-nonresonant situation is of particular interest to develop a vibrational spectroscopy of the molecular adsorbates. The other case of doubly resonant sum-frequency spectroscopy is shown to be a very powerful tool on molecular spectroscopy to identify the molecular parameters. As an example, the study of the Duschinsky rotation and its unique identification is treated explicitly. Finally, pumped sum-frequency spectroscopy is applied to stress the importance of the vibrational and electronic dephasing processes on the sum-frequency spectra, as well as on the determination of the time resolved profiles of the ground state population, obtained from these experiments.