arXiv subjects

Liang-You Peng

Publications and source records attributed to Liang-You Peng.

23 records · Page 2Linked to original sources

arXiv2006

An Efficient and Accurate Grid Method for Solving the Time-Dependent Schroedinger Equation: Application of Coulomb Wave Function DVR to Atomic Systems in Strong Laser Fields

We present an efficient and accurate grid method for solving the time-dependent Schrödinger equation of atomic systems interacting with intense laser pulses. As usual, the angular part of the wave function is expanded in terms of spherical harmonics. Instead of the usual finite difference (FD) scheme, the radial coordinate is discretized using the discrete variable representation which is constructed from the Coulomb wave function. For an accurate description of the ionization dynamics of atomic systems, the Coulomb wave function discrete variable representation (CWDVR) method needs 3-10 times less grid points than the FD method. The resultant grid points of CWDVR distribute unevenly so that one has finer grid near the origin and coarser one at larger distances. The other important advantage of the CWDVR method is that it treats the Coulomb singularity accurately and gives a good representation of continuum wave functions. The time propagation of the wave function is implemented using the well-known Arnoldi method. As examples, the present method is applied to the multiphoton ionization of both H and H$^-$ in intense laser fields. Short-time excitation and ionization dynamics of H by static electric fields is also investigated. For a wide range of photon energies and laser intensities, ionization rates calculated using this method are in excellent agreement with those from other theoretical calculations.

physics.atom-ph↗

arXiv2006

Attosecond signatures in photodissociation by an intense Ti:Sapphire pulse

In our model the electron dynamics are described by a two-state approximation. This might appear a rough approximation since it neglects coupling through excited electronic states and ionization channels. However at high intensity (laser fields equivalent to the Coulomb force) and long wavelength (photon energy much lower than the ionization potential) the dissociation process occurs by adiabatic polarization involving the lowest electronic states. For the experiment in question, with intensities above 10x14 W cm-2 and photon energies of 1.5eV, such an approach is well justified. More contentious is the neglect of rotational heating (that is molecular realignment) during the pulse. However, this process is essentially an internal relaxation and for a 50fs pulse it has a small effect. To calculate the dissociation spectrum, we have applied discretization methods developed for photoionization of molecules4) to solve the quantum equations in a dual configuration and momentum space. Technical details are discussed in the paper by Peng et al.

physics.atom-ph↗

arXiv2004

Dissociation spectrum of H$_2^+$ from a short, intense infrared laser pulse: vibration structure and focal volume effects

The dissociation spectrum of the hydrogen molecular ion by short intense pulses of infrared light is calculated. The time-dependent Schrödinger equation is discretized and integrated in position and momentum space. For few-cycle pulses one can resolve vibrational structure that commonly arises in the experimental preparation of the molecular ion from the neutral molecule. We calculate the corresponding energy spectrum and analyze the dependence on the pulse time-delay, pulse length, and intensity of the laser for $λ\sim 790$nm. We conclude that the proton spectrum is a both a sensitive probe of the vibrational dynamics and the laser pulse. Finally we compare our results with recent measurements of the proton spectrum for 55 fs pulses using a Ti:Sapphire laser ($λ\sim 790 $nm). Integrating over the laser focal volume, for the intensity $I \sim 3 \times 10^{15}$W cm$^{-2}$, we find our results are in excellent agreement with these experiments.

physics.atom-ph↗

arXiv2004

A discrete time-dependent method for metastable atoms in intense fields

The full-dimensional time-dependent Schrodinger equation for the electronic dynamics of single-electron systems in intense external fields is solved directly using a discrete method. Our approach combines the finite-difference and Lagrange mesh methods. The method is applied to calculate the quasienergies and ionization probabilities of atomic and molecular systems in intense static and dynamic electric fields. The gauge invariance and accuracy of the method is established. Applications to multiphoton ionization of positronium and hydrogen atoms and molecules are presented. At very high intensity above saturation threshold, we extend the method using a scaling technique to estimate the quasienergies of metastable states of the hydrogen molecular ion. The results are in good agreement with recent experiments.

physics.atom-ph↗

arXiv2004

Dynamic tunnelling ionization of $H_2^+$ in intense fields

Intense-field ionization of the hydrogen molecular ion by linearly-polarized light is modelled by direct solution of the fixed-nuclei time-dependent Schrödinger equation and compared with recent experiments. Parallel transitions are calculated using algorithms which exploit massively parallel computers. We identify and calculate dynamic tunnelling ionization resonances that depend on laser wavelength and intensity, and molecular bond length. Results for $λ\sim 1064$ nm are consistent with static tunnelling ionization. At shorter wavelengths $λ\sim 790 $ nm large dynamic corrections are observed. The results agree very well with recent experimental measurements of the ion spectra. Our results reproduce the single peak resonance and provide accurate ionization rate estimates at high intensities. At lower intensities our results confirm a double peak in the ionization rate as the bond length varies.

physics.comp-ph↗