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Interference between different optical processes

Ce. Chen

Published Jan 1, 1991• 0 citations
OpenAlex

Abstract

This thesis reports an experimental study of an interference phenomenon between one-photon and three-photon 6s$\sp1$S$\sb0$-6p$\sp1$P$\sb1$ transition amplitudes in a vapor of atomic mercury. The interference was observed by monitoring the multiphoton ionization signal. Using a three-cell design we were able to separate the third-harmonic generation process and the interfering absorption processes such that we could externally control the relative phase between the two transition amplitudes and directly study the interference phenomena. We observed that the multiphoton ionization signal, which is a measure of the net transition moment, varied sinusoidally as the relative phase increased. Using an eight-electrode design to collect the electrons ionized at different positions along the beam axis around the focal region, we measured the phase shift of the interference due to the $\pi$ phase shift of a focused Gaussian beam propagating through the focal region. The experimental setup and the experimental procedure are discussed in detail. This new method can be used in the study of many phase sensitive processes including potential applications in coherent control of chemical reactions.

Related papers

Phase-sensitive multiphoton ionization

Ce Chen, Yi-Yian Yin, Daniel S. Elliott

We have demonstrated an interference between multiphoton ionization processes that results in a phase-sensitive enhancement or inhibition of the net ionization rate. We focus two laser beams, either of which can induce an atomic transition between the same two states, into a cell containing atomic mercury. One of the fields is at a wavelength of 185 nm and can linearly induce the 6s 1S0 → 6p 1P1 transition in mercury. The other field is at a wavelength precisely three times as long, and it can excite the 6p resonance by a three-photon process. The absorption of two additional visible photons ionizes the mercury. In the presence of both fields, the transition amplitudes interfere, and their relative phases become very important. Their phases can be controlled by controlling the phases of the optical fields inducing the transitions. Coherence between the two fields, vital for the interference, is ensured by generating one field from the other using a nonlinear third-harmonic process. We have also demonstrated the effect of spatial phase variations between the two fields on the local photo-ionization rate.

Annual Meeting Optical Society of America•Jan 1, 1990•0 citations

Measurements of optical phase variations using interfering multiphoton ionization processes

Ce Chen, Daniel S. Elliott

We have used interfering multiphoton ionization processes to measure changes in the relative phase between two optical laser beams. In this work, the phase variation is due to the \ensuremath{\pi} phase shift of a focused Gaussian beam as it propagates through the focal region. An array of linear collection electrodes is used to measure the multiphoton ionization rate as a function of the distance from the beam waist when two laser fields are resonant with an atomic transition, one through a linear process, the other through a three-photon process.

Physical Review Letters•Oct 1, 1990•174 citations

Propagation effects in two-color coherent-control processes

Ce Chen, Daniel S. Elliott

We have investigated a two-color coherent-control process at high densities of the absorbing medium. Irradiating a vapor of atomic mercury with a coherent field, with one component nearly resonant with the three-photon 6s${\mathrm{}}^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6p${\mathrm{}}^{1}$${\mathit{P}}_{1}^{\mathit{o}}$ transition, and the other component the third harmonic of the first, we observe the interference between the two excitation pathways for this transition. Measurements of this interaction as the density of the mercury vapor is increased show evidence of nonlinear coupling (phase and amplitude locking) of the two field components with each other. This is manifested as a decrease in the magnitude of the photoionization signal, as well as a decrease of the depth of modulation of the photoionization signal. \textcopyright{} 1996 The American Physical Society.

Physical Review A•Jan 1, 1996•17 citations

Interference between optical transitions

Ce Chen, Yi-Yian Yin, Daniel S. Elliott

We report observations of an interference between optical transition amplitudes for linear and nonlinear excitation of the mercury 6s $^{1}\mathrm{S}_{0}$\ensuremath{\rightarrow}6p $^{1}\mathrm{P}_{1}$ transition. The transition probability is varied sinusoidally by changing the relative phase of the two fields inducing these distinct processes.

Physical Review Letters•Jan 29, 1990•315 citations

Coherent control of atomic photoionization

Stefano Cavalieri, R. Eramo, Luca Fini +1 more

Coherent control provides a quantum interference based method for controlling atomic and molecular dynamics. We report two experimental observations of different ways to achieve such a control in atomic photoionization continuum. One is the photoionization of sodium atoms, initially prepared in the 3P1/2 excited state, by a non resonant three-photon interaction with 1064-nm laser light and by a one-photon interaction with the third-harmonic field, at 355 nm. Interference between the two transition paths allows the control of the total ionization rate by varying the relative phase of the laser fields. The second experiment is the observation of the modification of the ionization continua of xenon through laser induced continuum structure (LICS). The multiphoton radiative decay of the xenon ground state into the two electronic continua, that correspond to the two fine structure levels of the ground state of the xenon ion, is varied by electromagnetically embedding a bound state of the atom into the two continua. Both experiments are performed on an atomic beam apparatus which uses a time-of-flight spectrometer for energy analyzing the emitted photoelectrons.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Oct 21, 1998•0 citations

Product state control through interfering optical ionization routes

Feng Yun Wang

In this thesis we report an experimental study of the effect of interference between two two-photon bound-to-free excitation routes in atomic barium from the $\rm 6s\sp2\ \sp1S\sb0$ ground state. Different final products of the transition were observed by monitoring the kinetic energy spectrum of the photoelectrons using a Time-of-Flight electron detector. By tuning the frequency of one of the laser sources used for this work, we were able to change the interference from constructive to destructive, and to demonstrate a strong control over the final product states. Because it only requires two independent tunable laser fields (mutually incoherent), this technique of using quantum interference for product control is very robust. We also studied the dependence of this interference effect and product control on several experimental parameters: the density of the atomic beam, the pulse energy of the lasers, the polarization state of the lasers and the selection of intermediate states. When the density of the atomic beam was increased, we observed that the strength of the interference and the degree of product control increased significantly. When the relative polarization of the two laser fields was changed from parallel to perpendicular, the strength of interference effect increased, but the product control disappeared. In this thesis, we describe the interference, our ability to control product distributions through this interference, and the dependence of interference and product state control on the various experimental parameters.

•Jan 1, 1996•0 citations
This thesis reports an experimental study of an interference phenomenon between one-photon and three-photon 6s\sp1\sp1\sp1S\sb0\sb0\sb0-6p\sp1\sp1\sp1P\sb1\sb1\sb1 transition amplitudes in a vapor of atomic mercury. The interference was observed by monitoring the multiphoton ionization signal. Using a three-cell design we were able to separate the third-harmonic generation process and the interfering absorption processes such that we could externally control the relative phase between the two transition amplitudes and directly study the interference phenomena. We observed that the multiphoton ionization signal, which is a measure of the net transition moment, varied sinusoidally as the relative phase increased. Using an eight-electrode design to collect the electrons ionized at different positions along the beam axis around the focal region, we measured the phase shift of the interference due to the π\piπ phase shift of a focused Gaussian beam propagating through the focal region. The experimental setup and the experimental procedure are discussed in detail. This new method can be used in the study of many phase sensitive processes including potential applications in coherent control of chemical reactions.
We have demonstrated an interference between multiphoton ionization processes that results in a phase-sensitive enhancement or inhibition of the net ionization rate. We focus two laser beams, either of which can induce an atomic transition between the same two states, into a cell containing atomic mercury. One of the fields is at a wavelength of 185 nm and can linearly induce the 6s 1S0 → 6p 1P1 transition in mercury. The other field is at a wavelength precisely three times as long, and it can excite the 6p resonance by a three-photon process. The absorption of two additional visible photons ionizes the mercury. In the presence of both fields, the transition amplitudes interfere, and their relative phases become very important. Their phases can be controlled by controlling the phases of the optical fields inducing the transitions. Coherence between the two fields, vital for the interference, is ensured by generating one field from the other using a nonlinear third-harmonic process. We have also demonstrated the effect of spatial phase variations between the two fields on the local photo-ionization rate.
We have used interfering multiphoton ionization processes to measure changes in the relative phase between two optical laser beams. In this work, the phase variation is due to the \ensuremath{\pi} phase shift of a focused Gaussian beam as it propagates through the focal region. An array of linear collection electrodes is used to measure the multiphoton ionization rate as a function of the distance from the beam waist when two laser fields are resonant with an atomic transition, one through a linear process, the other through a three-photon process.
We have investigated a two-color coherent-control process at high densities of the absorbing medium. Irradiating a vapor of atomic mercury with a coherent field, with one component nearly resonant with the three-photon 6s1{\mathrm{}}^{1}1S0{\mathit{S}}_{0}S0​\ensuremath{\rightarrow}6p1{\mathrm{}}^{1}1P1o{\mathit{P}}_{1}^{\mathit{o}}P1o​ transition, and the other component the third harmonic of the first, we observe the interference between the two excitation pathways for this transition. Measurements of this interaction as the density of the mercury vapor is increased show evidence of nonlinear coupling (phase and amplitude locking) of the two field components with each other. This is manifested as a decrease in the magnitude of the photoionization signal, as well as a decrease of the depth of modulation of the photoionization signal. \textcopyright{} 1996 The American Physical Society.
We report observations of an interference between optical transition amplitudes for linear and nonlinear excitation of the mercury 6s 1S0^{1}\mathrm{S}_{0}1S0​\ensuremath{\rightarrow}6p 1P1^{1}\mathrm{P}_{1}1P1​ transition. The transition probability is varied sinusoidally by changing the relative phase of the two fields inducing these distinct processes.
Coherent control provides a quantum interference based method for controlling atomic and molecular dynamics. We report two experimental observations of different ways to achieve such a control in atomic photoionization continuum. One is the photoionization of sodium atoms, initially prepared in the 3P1/2 excited state, by a non resonant three-photon interaction with 1064-nm laser light and by a one-photon interaction with the third-harmonic field, at 355 nm. Interference between the two transition paths allows the control of the total ionization rate by varying the relative phase of the laser fields. The second experiment is the observation of the modification of the ionization continua of xenon through laser induced continuum structure (LICS). The multiphoton radiative decay of the xenon ground state into the two electronic continua, that correspond to the two fine structure levels of the ground state of the xenon ion, is varied by electromagnetically embedding a bound state of the atom into the two continua. Both experiments are performed on an atomic beam apparatus which uses a time-of-flight spectrometer for energy analyzing the emitted photoelectrons.
In this thesis we report an experimental study of the effect of interference between two two-photon bound-to-free excitation routes in atomic barium from the $\rm 6s\sp2\ \sp1S\sb0$ ground state. Different final products of the transition were observed by monitoring the kinetic energy spectrum of the photoelectrons using a Time-of-Flight electron detector. By tuning the frequency of one of the laser sources used for this work, we were able to change the interference from constructive to destructive, and to demonstrate a strong control over the final product states. Because it only requires two independent tunable laser fields (mutually incoherent), this technique of using quantum interference for product control is very robust. We also studied the dependence of this interference effect and product control on several experimental parameters: the density of the atomic beam, the pulse energy of the lasers, the polarization state of the lasers and the selection of intermediate states. When the density of the atomic beam was increased, we observed that the strength of the interference and the degree of product control increased significantly. When the relative polarization of the two laser fields was changed from parallel to perpendicular, the strength of interference effect increased, but the product control disappeared. In this thesis, we describe the interference, our ability to control product distributions through this interference, and the dependence of interference and product state control on the various experimental parameters.