A. Yu. Naumov

Experimental study of drilling sub-10 μm holes in thin metal foils with femtosecond laser pulses

Aluminum foils with thickness ranging from 1.5 to 50 μm, and W, Mo, Ti, Cu, Fe, Ag, Au, and Pb foils of 25 μm thickness have been drilled with femtosecond Ti:sapphire laser pulses centered at 800 nm. The influence of laser parameters and material properties on hole drilling processes at sub-10 μm scale has been examined. A simple model is shown to predict the ablation rate for a range of metals.

Molecular Frame Reconstruction Using Time-Domain Photoionization Interferometry

Claude Marceau, Varun Makhija, Dominique Platzer, A. Yu. Naumov, P. B. Corkum, Albert Stolow, 3, 4 David Villeneuve, and Paul Hockett ∗ Joint Attosecond Science Laboratory, National Research Council of Canada and University of Ottawa, 100 Sussex Drive, Ottawa, K1A 0R6, Canada Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, ON K1N 6N5, Canada Department of Chemistry, University of Ottawa, 10 Marie Curies, Ottawa, ON K1N 6N6, Canada National Research Council of Canada, 100 Sussex Drive, Ottawa, K1A 0R6, Canada

Octave-spanning hyperspectral coherent diffractive imaging in the extreme ultraviolet range

Soft x-ray microscopy is a powerful imaging technique that provides sub-micron spatial resolution, as well as chemical specificity using core-level near-edge x-ray absorption fine structure (NEXAFS). Near the carbon K-edge (280-300 eV) biological samples exhibit high contrast, and the detailed spectrum contains information about the local chemical environment of the atoms. Most soft x-ray imaging takes place on dedicated beamlines at synchrotron facilities or at x-ray free electron laser facilities. Tabletop femtosecond laser systems are now able to produce coherent radiation at the carbon K-edge and beyond through the process of high harmonic generation (HHG). The broad bandwidth of HHG is seemingly a limitation to imaging, since x-ray optical elements such as Fresnel zone plates require monochromatic sources. Counter-intuitively, the broad bandwidth of HHG sources can be beneficial as it permits chemically-specific hyperspectral imaging. We apply two separate techniques - Fourier transform spectroscopy, and lensless holographic imaging - to obtain images of an object simultaneously at multiple wavelengths using an octave-spanning high harmonic source with photon energies up to 30 eV. We use an interferometric delay reference to correct for nanometer-scale fluctuations between the two HHG sources.

Ultrafast Dissociation of Metastable CO2+ in a Dimer

We triply ionize the van der Waals bound carbon monoxide dimer with intense ultrashort pulses and study the breakup channel (CO)_{2}^{3+}→C^{+}+O^{+}+CO^{+}. The fragments are recorded in a cold target recoil ion momentum spectrometer. We observe a fast CO^{2+} dissociation channel in the dimer, which does not exist for the monomer. We found that a nearby charge breaks the symmetry of a X^{3}Π state of CO^{2+} and induces an avoided crossing that allows a fast dissociation. Calculation on the full dimer complex shows the coupling of different charge states, as predicted from excimer theory, gives rise to electronic state components not present in the monomer, thereby enabling fast dissociation with higher kinetic energy release. These results demonstrate that the electronic structure of molecular cluster complexes can give rise to dynamics that is qualitatively different from that observed in the component monomers.

Interferometric time delay correction for Fourier transform spectroscopy in the extreme ultraviolet

We demonstrate a Fourier transform spectrometer in the extreme ultraviolet (XUV) spectrum using a high-harmonic source, with wavelengths as short as 32 nm. The femtosecond infrared laser source is divided into two separate foci in the same gas jet to create two synchronized XUV sources. An interferometric method to determine the relative delay between the two sources is shown to improve the accuracy of the delay time, with corrections of up to 200 asec required. By correcting the time base before the Fourier transform, the frequency resolution is improved by up to an order of magnitude.

Light amplification by seeded Kerr instability

Seeding a laser amplifier Amplification of femtosecond laser pulses requires a lasing medium or a nonlinear crystal. The chemical properties of the lasing medium or adherence to momentum conservation rules in the nonlinear crystal constrain the frequency and the bandwidth of the amplified pulses. Vampa et al. seeded modulation instability in a laser crystal pumped with femtosecond near-infrared pulses. This provided a method for the high gain amplification of broadband and short laser pulses up to intensities of 1 terawatt per square centimeter. The method avoids constraints related to doping and phase matching and can be expected to be applied to a wide pool of glasses and crystals. Science, this issue p. 673 Seeding optical instability in a laser crystal provides a flexible method of amplifying laser pulses. Amplification of femtosecond laser pulses typically requires a lasing medium or a nonlinear crystal. In either case, the chemical properties of the lasing medium or the momentum conservation in the nonlinear crystal constrain the frequency and the bandwidth of the amplified pulses. We demonstrate high gain amplification (greater than 1000) of widely tunable (0.5 to 2.2 micrometers) and short (less than 60 femtosecond) laser pulses, up to intensities of 1 terawatt per square centimeter, by seeding the modulation instability in an Y3Al5O12 crystal pumped by femtosecond near-infrared pulses. Our method avoids constraints related to doping and phase matching and therefore can occur in a wider pool of glasses and crystals even at far-infrared frequencies and for single-cycle pulses. Such amplified pulses are ideal to study strong-field processes in solids and highly excited states in gases.

Streak Camera for Strong-Field Ionization

Ionization of an atom or molecule by a strong laser field produces suboptical cycle wave packets whose control has given rise to attosecond science. The final states of the wave packets depend on ionization and deflection by the laser field, which are convoluted in conventional experiments. Here, we demonstrate a technique enabling efficient electron deflection, separate from the field driving strong-field ionization. Using a midinfrared deflection field permits one to distinguish electron wave packets generated at different field maxima of an intense few-cycle visible laser pulse. We utilize this capability to trace the scattering of low-energy electrons driven by the midinfrared field. Our approach represents a general technique for studying and controlling strong-field ionization dynamics on the attosecond time scale.