Anand Bahl

Assessment of the metastable electronic state approach as a microscopically self-consistent description for the nonlinear response of atoms

This Letter presents the first quantitative assessment of the recently proposed metastable electronic state approach (MESA) for calculation of the nonlinear optical response of noble gas atoms. Based on the single active electron potentials for several atomic species, Stark resonant states are used to extract the nonlinear polarization and ionization rates free of any additional fitting parameters. It is shown that even the simplest version of the method provides a viable, first-principle-based, and self-consistent alternative to the standard model commonly used for simulations in the field of extreme nonlinear optics.

On the convergence of quantum resonant-state expansion

Completeness of the system of Stark resonant states is investigated for a one-dimensional quantum particle with the Dirac-delta potential exposed to an external homogeneous field. It is shown that the resonant series representation of a given wavefunction converges on the negative real axis while the series diverges on the positive axis. Despite the divergent nature of the resonantexpansion, good approximations can be obtained in a compact spatial domain.

Reflectionless Beam Propagation on a Piecewise Linear Complex Domain

We describe a new class of transparent boundary conditions for beam-propagation simulation. The method is based on a transformation that breaks the original real-axis computational domain into a piecewise linear complex-plane contour, with higher-order analogues of Riemann-Cauchy conditions imposed at sharp corners of the contour. The resulting boundary conditions are extremely effective in terminating outgoing waves, and are easy to implement in an arbitrary beam-propagation method.

Nonlinear optical response in molecular nitrogen: from ab-initio calculations to optical pulse simulations

Using first-principle multi-electron calculations via the hybrid anti-symmetrized coupled channels method, we create a model to describe both the nonlinear polarization and ionization of the nitrogen molecule. Based on the metastable electronic state approach, it is designed for space-and-time-resolved simulations in nonlinear optics that require modeling of optical pulses that exhibit rich spectral dynamics and propagate over long distances. As a demonstration of the models utility, we study low-order harmonic generation in mid-infrared optical filaments.

Theory-experiment comparison of a quantum based light-matter interaction model for optical filamentation

We present an extensive, experiment-theory comparison of the Metastable Electronic State Approach to describe light-matter interaction in nonlinear optics. Excellent agreement validates the method for large-scale space-time resolved simulations.

Modeling of ultrafast laser pulse propagation

Computer simulations of ultrafast optical pulses face multiple challenges. This requires one to construct a propagation model to reduce the Maxwell system so that it can be efficiently simulated at the temporal and spatial scales relevant to experiments. The second problem concerns the light-matter interactions, demanding novel approaches for gaseous and condensed media alike. As the nonlinear optics pushes into new regimes, the need to honor the first principles is ever greater, and requires striking a balance between computational complexity and physical fidelity of the model. With the emphasis on the dynamics in intense optical pulses, this paper discusses some recent developments and promising directions in the field of ultrashort pulse modeling.