Ablation and transmission of thin solid targets irradiated by intense extreme ultraviolet laser radiation

The interaction of an extreme ultraviolet (EUV) laser beam with a parylene foil was studied by experiments and simulation. A single EUV laser pulse of nanosecond duration focused to an intensity of 3 × 1010 W cm−2 perforated micrometer thick targets. The same laser pulse was simultaneously used to diagnose the interaction by a transmission measurement. A combination of 2-dimensional radiation-hydrodynamic and diffraction calculations was used to model the ablation, leading to good agreement with experiment. This theoretical approach allows predictive modelling of the interaction with matter of intense EUV beams over a broad range of parameters

Picosecond absorption dynamics of photoexcited InGaP epitaxial films

Includes bibliographical references (page 92).The absorption recovery of a photoexcited InGaP epitaxial film 0.4 µm thick was investigated using the pump-probe laser technique and found to have a time constant of 55 ps at room temperature. Measurements done in the temperature range of 300-50 K show the decay of the photoexcited carrier distribution to be dominated by ambipolar diffusion and surface recombination. The measured absorption recovery time constant corresponds to an ambipolar diffusion coefficient D > 2.8 cm2/s and a surface recombination velocity of S > 4 × 105 cm/s at room temperature.This work was supported by the National Science Foundation grant (USA/Argentina) INT 8802563, the Air Force Office of Scientific Research (contract 89-0513), and the Center for Optoelectronic Computing Systems, sponsored by the National Science Foundation/Engineering Research Center grant ECD 9015128 and by the Colorado Advanced Technology Institute, an agency of the State of Colorado. C. S. Menoni acknowledges the support of the National Science Foundation grant ECS 9008899 and the CSU Faculty Research Grant

Table top nanopatterning with extreme ultraviolet laser illumination

Includes bibliographical references (pages 723-724).Patterning with extreme ultraviolet light generated by a compact, bright laser source operating at a wavelength of 46.9 nm is demonstrated using two complementary approaches: multiple beam interferometric lithography and de-magnifying projection. Features with sizes ranging from 370 nm to 60 nm were printed in a few seconds in poly-methyl methacrylate resist. These proof-of-principle experiments demonstrate practical table-top nanopatterning tools based on extreme ultraviolet lasers for nanotechnology applications

Nanometer-scale ablation with a table-top soft x-ray laser

Includes bibliographical references (page 3617).Ablation of holes with diameters as small as 82 nm and very clean walls was obtained in poly(methyl methacrylate) focusing pulses from a Ne-like Ar 46.9 nm compact capillary-discharge laser with a freestanding Fresnel zone plate diffracting into third order. These results demonstrate the feasibility of using focused soft x-ray laser beams for the direct nanoscale patterning of materials and the development of new nanoprobes

Generation and characterization of isolated attosecond pulses at 100 kHz repetition rate

The generation of coherent light pulses in the extreme ultraviolet (XUV) spectral region with attosecond pulse durations constitutes the foundation of the field of attosecond science. Twenty years after the first demonstration of isolated attosecond pulses, they continue to be a unique tool enabling the observation and control of electron dynamics in atoms, molecules, and solids. It has long been identified that an increase in the repetition rate of attosecond light sources is necessary for many applications in atomic and molecular physics, surface science, and imaging. Although high harmonic generation (HHG) at repetition rates exceeding 100 kHz, showing a continuum in the cutoff region of the XUV spectrum, was already demonstrated in 2013, the number of photons per pulse was insufficient to perform pulse characterization via attosecond streaking, let alone to perform a pump-probe experiment. Here we report on the generation and full characterization of XUV attosecond pulses via HHG driven by near-single-cycle pulses at a repetition rate of 100 kHz. The high number of 106 XUV photons per pulse on target enables attosecond electron streaking experiments through which the XUV pulses are determined to consist of a dominant single attosecond pulse. These results open the door for attosecond pump-probe spectroscopy studies at a repetition rate 1 or 2 orders of magnitude above current implementations

High-Efficiency 800 nm Multi-Layer Dielectric Gratings for High Average Power Laser Systems

We report on the design, fabrication, and performance of a 1740 l/mm multilayer dielectric diffraction grating for use with 800 nm light. At an input angle of 8{sup o} from Littrow and a wavelength from 770 to 830 nm, >90% diffraction efficiency is achieved, with peak diffraction efficiency of >97% at 800nm. We will also comment on laser damage threshold and power-handling properties

Modelling DNA at the mesoscale: a challenge for nonlinear science?

Invited paper, in the series "Open Problems" of NonlinearityInternational audienceWhen it is viewed at the scale of a base pair, DNA appears as a nonlinear lattice. Modelling its properties is a fascinating goal. The detailed experiments that can be performed on this system impose constraints on the models and can be used as a guide to improve them. There are nevertheless many open problems, particularly to describe DNA at the scale of a few tens of base pairs, which is relevant for many biological phenomena

Ion Beam Deposition of (NbTa)2O5/SiO2 Multilayers for High-Efficiency Dielectric Gratings for High Average Power Laser Systems Operating at 800 nm Central Wavelength

The ion beam deposition of (NbTa)2O5 has been investigated for realizing high reflectance multilayer stacks of high damage threshold for applications in the engineering of dielectric gratings for use at 800 nm. Deposition conditions were optimized to yield fully oxidized films as determined from x-ray photoelectron spectroscopy (XPS). The film properties were also investigated using spectroscopic ellipsometry, and spectrophotometry to determine their refractive index and thickness respectively. Damage threshold testing was performed on single films using an amplified Ti:Sapphire laser producing a train of 170 ps pulses at a wavelength of 800 nm with an average energy of 100 mJ. The laser output was focused at the surface of the samples via a 0.5 m focal length lens to generate fluences ranging from 0 to 9 J/cm{sup 2}. At the optimum deposition conditions for highest optical quality and damage threshold, high reflector stacks of (NbTa){sub 2}O{sub 5}/SiO2 were fabricated. These stacks were employed to fabricate dielectric gratings with 1740 l/mm for use with 800 nm light. At an input angle of 8{sup o} from Littrow and a wavelength from 770 to 830 nm, >90% diffraction efficiency is achieved, with peak diffraction efficiency of >97%. The demonstration of dielectric gratings at 800 nm is opening the pathway to significantly increase the power handling capabilities of grating compressors for picosecond and femtosecond chirped pulse amplifications systems

Ab initio study of the beta$-tin->Imma->sh phase transitions in silicon and germanium

We have investigated the structural sequence of the high-pressure phases of silicon and germanium. We have focussed on the cd->beta-tin->Imma->sh phase transitions. We have used the plane-wave pseudopotential approach to the density-functional theory implemented within the Vienna ab-initio simulation package (VASP). We have determined the equilibrium properties of each structure and the values of the critical parameters including a hysteresis effect at the phase transitions. The order of the phase transitions has been obtained alternatively from the pressure dependence of the enthalpy and of the internal structure parameters. The commonly used tangent construction is shown to be very unreliable. Our calculations identify a first-order phase transition from the cd to the beta-tin and from the Imma to the sh phase, and they indicate the possibility of a second-order phase-transition from the beta-tin to the Imma phase. Finally, we have derived the enthalpy barriers between the phases.Comment: 12 pages, 16 figure

Nanoimaging with a compact extreme-ultraviolet laser

Includes bibliographical references (page 2097).Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a freestanding imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology