Multiphoton transitions can be reached by many routes through a continuum of virtual levels. We show that the transition probability of two-photon and multiphoton processes can be controlled by tailoring the shape of an ultrashort excitation pulse, so that the many paths leading to the final state interfere to give a desired probability amplitude. We analyze the effect of pulse shapes on N-photon absorption as well as on Raman transitions. We show theoretically that certain tailored dark pulses do not excite the system at all, while other shaped pulses induce transitions as effectively as transform limited pulses, even when their peak amplitudes are greatly reduced. These results are confirmed experimentally for two-photon transitions in atomic cesium.Multiphoton transitions can be reached by many routes through a continuum of virtual levels. We show that the transition probability of two-photon and multiphoton processes can be controlled by tailoring the shape of an ultrashort excitation pulse, so that the many paths leading to the final state interfere to give a desired probability amplitude. We analyze the effect of pulse shapes on N-photon absorption as well as on Raman transitions. We show theoretically that certain tailored dark pulses do not excite the system at all, while other shaped pulses induce transitions as effectively as transform limited pulses, even when their peak amplitudes are greatly reduced. These results are confirmed experimentally for two-photon transitions in atomic cesium.

Physical Review AAug 1, 1999366 citations

Photoelectron angular distributions for the two-photon ionization of helium by ultrashort extreme ultraviolet free-electron laser pulses

Ruilin Ma, Koji Motomura, Kenichi L. Ishikawa +19 more

Phase-shift differences and amplitude ratios of the outgoing $s$ and $d$ continuum wave packets generated by two-photon ionization of helium atoms are determined from the photoelectron angular distributions obtained using velocity map imaging. Helium atoms are ionized with ultrashort extreme-ultraviolet free-electron laser pulses with a photon energy of 20.3, 21.3, 23.0, and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The measured values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to an excited level or Rydberg manifold. The difference stems from the competition between resonant and non-resonant paths in two-photon ionization by ultrashort pulses. Since the competition can be controlled in principle by the pulse shape, the present results illustrate a new way to tailor the continuum wave packet.Phase-shift differences and amplitude ratios of the outgoing $s$ and $d$ continuum wave packets generated by two-photon ionization of helium atoms are determined from the photoelectron angular distributions obtained using velocity map imaging. Helium atoms are ionized with ultrashort extreme-ultraviolet free-electron laser pulses with a photon energy of 20.3, 21.3, 23.0, and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The measured values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to an excited level or Rydberg manifold. The difference stems from the competition between resonant and non-resonant paths in two-photon ionization by ultrashort pulses. Since the competition can be controlled in principle by the pulse shape, the present results illustrate a new way to tailor the continuum wave packet.

arXiv:1204.4812Journal of Physics B Atomic Molecular and Optical PhysicsAug 13, 201321 citations

Two-Photon Laser Theory Near a Single-Photon Resonance

M. D. Reid, H. J. Carmichael, Daniel F. Walls

Springer eBooksJan 1, 19840 citations

Resonant Two-Photon Transitions

Pavel A Apanasevich, G. I. Timofeeva

Journal of Applied SpectroscopyMay 1, 20184 citations

Polarization four-wave mixing technique for measuring ultrashort pulses

Victor R. Blok, Gennady M. Krochik

We treat the problem of four-wave resonant mixing of ultrashort laser pulses in gaseous media. We show that for some transitions, for example, quadrupole transitions, the polarization effects can be strongly manifested. For four-wave two-photon resonant mixing we find that the signal-wave plane rotation depends on the parameters of the resonant medium and the pulses mixed. We show that for long pump pulses and short signal pulses in the ultrashort-pulse time domain the angle of rotation of the plane of polarization of the signal plane can reach several dozen degrees. We show that the effect of altering the state of polarization of the short signal pulse can be used for measuring its shape and duration. Since the polarization measurements are precise and the proposed regimes of four-wave mixing do not depend on phase and amplitude fluctuations of the measuring pulse, the polarization four-wave mixing technique can be more accurate than the technique widely used for such purposes, measurement of the second-order intensity correlation function. We also discuss new nonlinear spectroscopy for measuring fast resonant susceptibilities (in particular, second-order polarizabilities) of the medium, based on the rotation of the polarization plane or the polarization ellipse of the signal pulse.We treat the problem of four-wave resonant mixing of ultrashort laser pulses in gaseous media. We show that for some transitions, for example, quadrupole transitions, the polarization effects can be strongly manifested. For four-wave two-photon resonant mixing we find that the signal-wave plane rotation depends on the parameters of the resonant medium and the pulses mixed. We show that for long pump pulses and short signal pulses in the ultrashort-pulse time domain the angle of rotation of the plane of polarization of the signal plane can reach several dozen degrees. We show that the effect of altering the state of polarization of the short signal pulse can be used for measuring its shape and duration. Since the polarization measurements are precise and the proposed regimes of four-wave mixing do not depend on phase and amplitude fluctuations of the measuring pulse, the polarization four-wave mixing technique can be more accurate than the technique widely used for such purposes, measurement of the second-order intensity correlation function. We also discuss new nonlinear spectroscopy for measuring fast resonant susceptibilities (in particular, second-order polarizabilities) of the medium, based on the rotation of the polarization plane or the polarization ellipse of the signal pulse.

Journal of the Optical Society of America BNov 1, 19902 citations

Phase-shift differences and amplitude ratios of the outgoing

s

and

d

continuum wave packets generated by two-photon ionization of helium atoms are determined from the photoelectron angular distributions obtained using velocity map imaging. Helium atoms are ionized with ultrashort extreme-ultraviolet free-electron laser pulses with a photon energy of 20.3, 21.3, 23.0, and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The measured values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to an excited level or Rydberg manifold. The difference stems from the competition between resonant and non-resonant paths in two-photon ionization by ultrashort pulses. Since the competition can be controlled in principle by the pulse shape, the present results illustrate a new way to tailor the continuum wave packet.