[en] We present an experimental demonstration of extending the high-order harmonic cutoff photon energy more than a factor of 2 when the driving-field wavelength is changed from 0.8 to 1.51 μm with an optical parametric amplifier. With argon gas, the cutoff has been extended from 64 to 160 eV. We predict that coherent keV x rays can be generated by exciting helium gas with the long-wavelength driving pulses. Experiments on xenon gas with several pump wavelengths also showed the dramatic cutoff extension, as well as full tunability of the generated XUV wavelengths

[en] It was found experimentally with increasing the laser ellipticity that the intensity of the 45th order harmonic from O₂ decreases slower than that from N₂. The difference is attributed to the fact that the recombination probability is suppressed for O₂ but enhanced for N₂ in a linearly polarized field. Simulation results obtained by extending the Lewenstein model to molecules agreed qualitatively with the experimental discoveries

[en] High-order harmonic generation has been observed experimentally from O₂ molecules at the saturation ionization intensity. The harmonic cutoff extends far beyond the cutoff of Xe despite both have nearly equal ionization potentials. In contrast, the harmonic spectra for N₂ and Ar, which have almost the same ionization potentials, are essentially close to each other. We show the extension of harmonic cutoff in O₂ is a consequence of ionization suppression. Using a simple modified tunneling ionization model for molecules, we predict both the harmonic cutoff extension and the ionization suppression semiquantitatively

[en] Picosecond framing camera is one of the key diagnostic tools for laser produced plasma physics study because of its high temporal resolution and two dimensions spatial resolving ability. The technology of gating MCP in image intensifier with picosecond high voltage pulse for ultrahigh speed photography, has been developed worldwide during the last 10 years. High voltage pulse of 140 ps in width and 2.7 kV was generated to gate the multiframe images on a meander shape microstripline on MCP. The measurement time range was extended to 1.1 ns while the exposure time of each image is 60 ps. The measured spatial resolution of the framing camera is 25 lp/mm. New method to reduce the exposure time down to 10 ps was simulated numerically

[en] Concentrations of mercury and other heavy metals were measured in soils surrounding the Wuda Coalfield, Inner Mongolia where underground coal fires are regarded as an important contamination source. Soil samples at the downwind direction were nearly all enriched mercury in surface layers, with their concentrations ~ 10 times higher than those from upwind soils. Mercury concentrations generally increased along soil profiles upward, indicative of increasing atmospheric mercury deposition in recent decades. We suggest that underground coal fire emissions were the potential mercury contamination source and the key factor controlling mercury enrichment in soils. Other heavy metals showed no clear spatial and vertical trends, suggesting that underground coal fire emissions may not the main factor for their enrichment in soils. Antimony showed the highest enrichment followed by tin, while chromium, mercury and cadmium only exhibited slight enrichment. Risk evaluation indicated that heavy metals in the studied soils pose no ecological threats.

[en] The author describes the structure and principle of a X-ray picosecond framing camera. Also, the performance and critical techniques of camera are presented. 12 frame images of the laser produced plasma source are obtained with the camera

[en] An experiment is described in which an apparatus is used to demonstrate the feasibility of measuring multiphoton photoionization rates in the interaction of short pulsed lasers with atoms or molecules. With this methodology, the ionization rate is measured as a function of the spatial position in the beam-waist region of the laser through the direct three-dimensional spatial imaging of the ionization events. Thus, if the spatial dependence of the laser beam intensity were known, a series of experiments could yield the intensity dependence of multiphoton ionization without the assumptions or errors that are generally inherent in the integration over one or more dimensions in the laser focal volume