Probing atomic nature of molecular orbitals using Cooper minimum in the high harmonic spectrum
Unique light sources available at ALLS enables us to accurately determine the Cooper minimum (CM) in Ar by measuring the position of the intensity minimum in the high harmonic spectrum and to extend our studies to complex molecules. CM is an atomic phenomena that arises due to the interference between opposing contributions to photoionization when an atomic orbital has a radial node. Since molecular orbitals are derived from a linear combination of atomic orbitals a CM should exist in molecules. We demonstrate CM in S and Cl containing molecules and show that it varies with different molecular environment (see left figure). The shift in CM to higher energies is due to a decrease in the atomic character of the orbitals as Cl atoms are replaced by H and C.
M. C. H. Wong, A.-T. Le, A. F. Alharbi, A. E. Boguslavskiy, R. R. Lucchese, J.-P. Brichta, C. D. Lin, and V. R. Bhardwaj, High Harmonic Spectroscopy of the Cooper Minimum in Molecules, Phys. Rev. Lett. 110, 033006 (2013).
Wavelength Scaling of Terahertz Generation by Gas Ionization.
A group of researchers from INRS-ÉMT, comprising members from the team of Profs. R. Morandotti (project’s supervisor), F. Légaré, and T. Ozaki, and more specifically the postdoctoral fellow M. Clerici and collaborators from foreign institutions (A. Lotti, A. Couairon, D. Faccio), have shown that the THz flux emitted from a plasma increases with the scaling law λ5. Therefore, with a laser at 1.8 micron wavelength, the THz flux obtained with 1 mJ of energy per pulse is the same as for 60 mJ per pulse at 800 nm. This scaling law shows that it is highly advantageous to use infrared laser source to drive THz generation from plasma, and is a clear motivation to develop intense laser sources in the mid-infrared spectral range. For more information, see:
M. Clerici, M. Peccianti, B. E. Schmidt, L. Caspani, M. Shalaby, M. Giguère, A. Lotti, A. Couairon, F. Légaré, T. Ozaki, D. Faccio, et R. Morandotti, Wavelength Scaling of Terahertz Generation by Gas Ionization, Phys. Rev. Lett. 110, 253901 (2013).
The graph shows the recorded THz energy as a function of the pump wavelength (solid circle). The red solid curve shows the power law fit λ4,5 ± 0,5. The upper inset shows the experimental setup: the output from an optical parametric amplifier (OPA) is focused together with its second harmonic generated by a BBO crystal. The generated THz pulse is collected by a parabolic imaging system and focused into the detection setup. The time-resolved electric field is detected via air-biased-coherent-detection (ABCD) and is shown in the lower inset.
Frequency domain Optical Parametric Amplification (FOPA).
Within the last decade, several approaches have been developed to generate intense few-cycle laser pulses. The amplification of those laser pulses remains a technological challenge. In 2012-2013, a team of researchers from INRS-ÉMT under the direction of Prof. F. Légaré (Drs. B. E. Schmidt and H. Ibrahim) have proposed a new approach called Frequency domain Optical Parametric Amplifier, and the intelectual property has been protected by INRS. This new approach has successfully been demonstrated using the ALLS infrastructure through a collaboration with Prof. Ozaki. Furthermore, a manuscript is under revision.
Method and system for high power parametric amplification of ultra-broadband few-cycle laser pulses, PCT/CA2012/050557. Authors: Schmidt, B. E., Légaré, F., Ibrahim, H. Registration date: August 17 2012.
“Frequency domain Optical Parametric Amplification”, B. E. Schmidt, N. Thiré, M. Boivin, A. Laramée, F. Poitras, G. Lebrun, T. Ozaki, H. Ibrahim, F. Légaré (submitted, 2013).