Few-Cycle Vortex Pulses
Study of OAM-dependent ATI using two-color and tightly focused pulses.
Research
Strong-Field Ionization & Quantum Dynamics
Theory of Above-Threshold Ionization, Nondipole Effects, and Twisted-Light Interactions
My research focuses on the theoretical description of how atoms interact with ultra-intense laser fields ranging from 1013–1018 W/cm2. Using analytical methods—such as the strong-field approximation (SFA), saddle-point techniques in complex time, Jacobi–Anger expansions—and comparisons with numerical solutions of the time-dependent Schrödinger equation, I study how electrons absorb multiple photons, tunnel through distorted Coulomb barriers, and form rich interference structures in momentum space.
Above-Threshold Ionization (ATI)
In strong fields, an electron can absorb more photons than needed to escape, producing characteristic ATI peaks and complex fringe patterns in the photoelectron momentum distribution (PMD).
Major Contributions:
- Developed analytical models for ATI using both the Jacobi–Anger expansion and saddle-point SFA.
- Explained how few-cycle pulses modify ATI peak spacing and suppress even/odd photon channels.
- Demonstrated how pulse duration and carrier-envelope phase (CEP) shape sub-cycle emission timing.
- Provided accurate predictions of ATI shifts by incorporating nondipole (magnetic field) effects.
Saddle-Point Methods & Complex-Time Trajectories
The saddle-point approximation reveals quantum trajectories in the complex-time plane—each corresponding to a physical ionization pathway.
Methodological Developments:
- Extended saddle-point SFA to short pulses where the standard stationary-phase approach fails.
- Identified the origin of sub-cycle interference through competing complex-time ionization paths.
- Compared saddle-point solutions with full Jacobi–Anger expansions, showing when each method is accurate.
- Mapped the deformation of integration contours around branch cuts for nondipole strong-field ionization.
Nondipole & Relativistic Effects
At long wavelengths (e.g., 3200–4200 nm) and high intensities, the dipole approximation breaks down. The magnetic field shifts the electron’s momentum opposite to the laser propagation direction.
Key Scientific Results:
- Formulated nondipole strong-field approximation (including k · r phase and magnetic drift).
- Explained the forward–backward momentum asymmetry observed in mid-IR experiments.
- Showed why few-cycle pulses match experiments better than monochromatic models.
- Analyzed linear-photon-momentum partitioning between ion and electron during ATI.
Twisted Light & Orbital Angular Momentum (OAM)
Vortex laser pulses carry orbital angular momentum, enabling structured photoelectron emission patterns that cannot be produced by plane waves.
Research Contributions:
- Computed PMDs for few-cycle Bessel (twisted) beams in both dipole and nondipole regimes.
- Demonstrated selection rules for OAM transfer to electrons in strong fields.
- Analyzed saddle-point structures unique to vortex pulses, including ring-shaped field maxima.
- Developed the SFA formalism for twisted beams using Jacobi–Anger and saddle-point approaches.
Current & Future Directions
Improved Strong-Field Models
Incorporating Coulomb-distorted Volkov states to improve low-energy predictions.
Partial-Wave Expansion in Nondipole Regime
Extending angular-momentum–resolved frameworks beyond dipole SFA.
I am open to discussions and collaborations in strong-field physics, quantum dynamics, and computational AMO theory. Contact me.