The generation of attosecond extreme ultraviolet (XUV) pulses in atomic and molecular gases based on high harmonic generation(HHG) has attracted considerable attentions for its potential use of probing the structure and ultrafast electron dynamics in matters with unprecedented temporal and spatial resolutions. The application of the XUV pulses can be summarized into two categories. In the first category, during the HHG process, the recolliding electron wavepacket encodes information on the generating molecule in the emitted harmonics. Thus the harmonic signal is used to retrieve temporal and structural insight into the generating targets itself, known as ”self-probing” schemes. On the other hand, the availability of isolated attosecond XUV pulses extends the femtosecond spectroscopy and femto-chemistry to the attosecond domain, which is the natural time scale of the electron motion. Also, it was recently shown that the attosocond XUV pulses could also provide Angstorm resolved images of electron wavepackets in molecules.
The ultrafast optics group led by Prof. Peixiang Lu has presented a systematic study of ultrafast imaging of molecular orbitals with different symmetries using MAPD technique. time-dependent Schrodinger equation (TDSE) within Born Oppenheimer (BO) approximation. Clear diffraction patterns appear in PMD. The internuclear distance can be determined with respect to the position of interference fringes. By stretching the molecules, the diffraction patterns change accordingly which in turn determine the change of internuclear distance with high precision. Furthermore, the detailed structure of the interference image, i.e., the relative heights of the interference fringes reflects the structure information of molecular orbitals. Using a simple two-center interference model, we successfully reproduced the difference pattern and it shows good agreement with the TDSE calculations. These results enable us to retrieve the molecular orbital for PAD with an inversion algorithm invoking the symmetry of the initial molecular orbital.
This work was supported by the 973 Program of China under Grant No. 2011CB808103, the NNSF of China under Grants No. 11404123, 11234004, and 61275126, the Doctoralfund of Ministry of Education of China under Grant No. 20100142110047. This work is published on Opt. Express Vol. 23, No. 8, 10688 (2015).
Figure The sketch of molecular attosecond photoelectron diffraction.