Self-probing of molecules with high harmonic generation

Abstract

This tutorial presents the most important aspects of the molecular self-probing paradigm, which views the process of high harmonic generation as "a molecule being probed by one of its own electrons". Since the properties of the electron wavepacket acting as a probe allow a combination of attosecond andÅngström resolutions in measurements, this idea bears great potential for the observation, and possibly control, of ultrafast quantum dynamics in molecules at the electronic level. Theoretical as well as experimental methods and concepts at the basis of self-probing measurements are introduced. Many of these are discussed on the example of molecular orbital tomography.

Influence of large permanent dipoles on molecular orbital tomography

“…In addition, one should also calculated or measure the high-order harmonic spectrum from the reference atom with the ionization energy similar to that of the target molecule. Then the recombination dipole moment d L and the dipole velocity d V for the molecular orbital in both x' and y' components are obtained by [7] …”

“…For symmetric molecules, the same orbital can in principle be reconstructed from both the x and y components of the dipole moments (d L x and d L y ). However, due to the limited discrete sampling in Fourier space, they will most likely not give the same result [7]. Generally, the final reconstructed orbital is defined as…”

“…By applying this method to a series of aligned molecules, they accomplished a tomographic reconstruction of the highest occupied molecular orbital (HOMO) of N 2 . Since then, the MOT has attracted a great deal of attention for its great significance in uncovering the basic properties of molecules and chemical reactions [7][8][9][10][11][12][13]. In most of the works, the target molecular orbitals are symmetric with either gerade or ungerade symmetry, while the MOT of nonsymmetric orbitals is more difficult.…”

“…Therefore, they suggested using extremely short few-cycle laser pulses to ensure the oneside-recollision and the molecular orbital of HeH 2+ was successfully reconstructed in their simulation. Besides, one can also consider using an ω + 2ω two-color laser pulse for the MOT of nonsymmetric orbitals [7,17].…”

The impact of the carrier envelope phase-dependence on system and laser parameters

“…This opens the door to a great variety of new investigations such as time-resolved measurement of electronic processes or precision control of chemical reactions see, e.g., [3,4,5,6,7,8,9]. One of the main new aspects of such few-cycle pulses is that the Carrier Envelope Phase (CEP), i.e.…”