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We use counterpropagating pulse trains to selectively enhance high-order harmonic generation from 70eV to 145eV using all-optical quasi phase matching. Enhancement factors up to x400 are obtained.

The process of high-order harmonic generation (HHG) can be used to generate bright, coherent beams of light in the extreme-ultraviolet and soft x-ray region of the spectrum by upconverting intense femtosecond pulses to very short wavelengths. These high-order harmonics result from ionization of the gas used as a nonlinear medium; thus, a full understanding of the process involves incorporating atomic physics, quantum dynamics, and plasma physics into an already non-trivial nonlinear optics problem. In the past several years, we have developed a new technology of "extreme" nonlinear optics that uses the rich, attosecond time-scale physics of the process in novel ways to manipulate the characteristics of this source, improving both the flux and the spectral characteristics. Most recently, we have (1) demonstrated that quasi phase matching of the high-order harmonic conversion process can be accomplished by the use of weak counterpropagating pulse trains that modulate the conversion process, constituting a nonlinear-optical "crystal" made of light; and (2) we have demonstrated that high-order harmonics can be generated by ionization of ions in a guided-wave geometry, using a discharge- created plasma waveguide to pre-ionize the gas and form a guiding electron density profile. High-order harmonic generation (HHG) driven by ultrashort laser pulses is a source of extreme-ulraviolet and soft x-ray light with the unique properties of ultrashort pulse duration and high spatial and temporal coherence. 1 This source has made possible a number of new ultrafast spectroscopic probes of atoms, molecules and materials. To date, however, most applications use relatively long wavelengths (>10nm), due to the fact that the efficiency of the HHG process decreases rapidly at shorter wavelengths. This decrease in efficiency is not due primarily to the very high-order nonlinearity of the process, but as a result of the phase mismatch between the fundamental laser field and high order harmonic field. Dispersion of the free-electron plasma produced by ionization creates a phase mismatch that speeds up the phase velocity of the driving laser with respect to the generated harmonics, and that cannot be compensated using conventional phase matching techniques. This limits efficient harmonic generation to

We present the first demonstration of high harmonic flux enhancement (over an order of magnitude) using quasi-phase-matching by a counterpropagating pulse train. This was enabled by a waveguide geometry. We also demonstrate quantum path control.

e20076 Background: Mucosal melanoma is rare in Caucasian but account for 25% in Asian population and usually associated with poor prognosis. No standard treatment for advanced mucosal melanoma has ...

The commercial software ANSYS CFX is used for modeling the hydrodynamic characteristics of submarine-launched vehicle. In the numerical simulations, the SST (Shear Stress Transport) turbulence model is employed to describe the turbulence phenomenon occurring in the continuous fluid. The Rayleigh-Plesset equa- tions are applied to analyze the cavitation phenomenon. Three-dimensional numerical simulation was carried out to study the cavity shape, the surface pressure distribution and the drag force with different flow control. The result shows that the gas and the number of ventilation holes control to show any significant impact on the cavity shape and the surface pressure are effective measures to decrease resistance.

We use counterpropagating light to directly observe the coherent buildup of high harmonic generation in a hollow waveguide geometry. We measure, for the first time, coherence lengths for high photon energies that cannot be phase matched using conventional approaches. We also probe the transition through phase matching, the ionization level at which different harmonic orders are generated, and the change in the coherence length as the driving laser is depleted. These results directly prescribe the optimal structures or pulse trains required for implementing quasiphase matching.

We present new results on the use of low-loss, deeply modulated waveguides to enhance the flux of high harmonic emission at short wavelengths. This is achieved by quasi-phase matched frequency conversion to increase the coherence length.

High harmonic generation (HHG) is a useful source of coherent light in the extreme ultraviolet (EUV) region of the spectrum. However, both the conversion efficiency and the highest achievable photon energy have in the past been limited in the past by the inability to phase-match the frequency conversion process. In this paper, we summarize recent results on the development of new techniques for phase-matching the high-harmonic conversion process. We also summarize finding from three series of experiments that make use of the coherent EUV light generated using HHG: 1) probing of acoustic dynamics in materials; 2) monitoring of chemical dynamics at surfaces using photoelectron spectroscopy; and 3) time-resolved plasma imaging.

We demonstrate that light generated using high-harmonic conversion in waveguides has very high spatial coherence at 30 nm and 13nm. Using this light source, we demonstrate EUV images of the explosion of a micron-size water droplet illuminated by an intense femtosecond laser using an all-reflective, double-multilayer mirror setup and a CCD camera as an image recording device.

A novel design, magnetically focused, x‐ray streak camera was designed and tested using sub‐20 fs soft‐x‐ray pulses generated by high harmonic emission in a gas. The temporal resolution of the camera was demonstrated to be under 0.9 ps throughout the ultraviolet to soft‐x‐ray wavelength region. Our streak camera represents the fastest x‐ray detector developed to date.

We present a simple setup for obtaining high resolution, sub-micron images using high harmonic generation (HHG) in a hollow-core waveguide as a light source. We demonstrate imaging with illumination at a wavelength of 30 nm using an all-reflective, double-multilayer mirror setup and a CCD camera as a recording device. For the magnifications of up to 50x used here, the all-reflective setup has advantages over zone plate microscopes because of the much larger working distances that allow for imaging of plasmas. This setup has also a throughput that is higher by at least a factor of three compared to zone-plate microscopes, and presents the additional advantage of preserving the temporal pulse width of the harmonics because diffractive optics are not used. This work demonstrates the feasibility of high-spatial-resolution, time-resolved, EUV imaging of plasmas and other objects using a tabletop compact light source.

By measuring the fringe visibility in a Young's double pinhole experiment, we demonstrate that quasi-phase-matched high-harmonic generation produces beams with very high spatial coherence at wavelengths around 13 nm. To our knowledge these are the highest spatial coherence values ever measured at such short wavelengths from any source without spatial filtering. This results in a practical, small-scale, coherent, extreme-ultraviolet source that is useful for applications in metrology, imaging, and microscopy.

A diode-pumped, compact, wavelength tunable, single frequency Er3:Yb3 codoped DBR fiber laser is reported.An output power of 2.4mW for 75mW of 980nm diode pump power and a slope efficiency of 6% at 1 557.O5nmwere obtained. Linewidth of the laser was estimated at 1557.O5nm to be less than 1MHz. Also, the laser can betuned to wavelengths between 1557nm to 156mm and operates single mode throughout this range.Keywords: wavelength tunable, single frequency, fiber laser

The self-injection locking single frequency Yb-doped fiber ring laser is reported. The system shows compact, stable and tunable. In the primary experiment, the Self-injection locking single frequency fiber ring laser with wavelength 1.05325)mum, power exceeding 3.5mW,line-width less than 36 MHz was manufactured. The laser shows stability, low threshold and high power. No mode-hopping was observed within 2 hours. The single polarization output can be obtained when use single polarization fiber.

MCM-48 nanoparticle-embedded polymer nanofibers (NPNFs) were prepared from the PVP solution containing MCM-48 nanoparticles (NPs) by the electrospinning technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) were used to characterize the composition and morphology of electrospun nanofibers. The results showed that the average diameter of MCM-48 NPNFs was about 500 nm. Photoluminescence (PL) and phosphorescence properties were investigated by fluorescence spectrofluorometer. MCM-48 NPNFs exhibited a bright blue-green emission at ∼420 nm, followed by a long-lifetime blue-green phosphorescence at ∼480 nm, which can be fitted by a bi-exponential decay process with lifetimes of 3.24 s and 1.22 s at room temperature. The triplet-to-singlet transition is responsible for the blue-green emission around 420 nm of the MCM materials, while the phosphorescence at ∼480 nm is probably due to the oxygen-related vacancies on the surface, which act as a capture trap.

We show through experiment and calculations how all-optical quasi-phase-matching of high-order harmonic generation can be used to selectively enhance emission from distinct quantum trajectories at high photon energies. Electrons rescattered in a strong field can traverse short and long quantum trajectories that exhibit differing coherence lengths as a result of variations in intensity of the driving laser along the direction of propagation. By varying the separation of the pulses in a counterpropagating pulse train, we selectively enhance either the long or the short quantum trajectory, and observe distinct spectral signatures in each case. This demonstrates a new type of coupling between the coherence of high-order harmonic beams and the attosecond time-scale quantum dynamics inherent in the process.

Phase matching is a necessity, but what happens in the extreme? Can we use the nonlinear processes to create the necessary phase matching?

We formulate a theory of quasi-phase matching of high harmonic generation using weak counterpropagating pulse trains. We predict the optimal laser intensities and pulse shapes for the counterpropagating field and find that the conversion efficiency is better than the efficiency obtained by simply suppressing harmonic emission from out-of-phase regions.

Epstein-Barr virus (EBV) is closely associated with nasopharyngeal carcinoma (NPC), which occurs with highest incidence in Guangdong areas. However, EBV is ubiquitous and remains a life-long asymptomatic infection in the peripheral B lymphocytes of healthy carriers; thus it is supposed that there is a substrain of EBV with carcinogenesis potential in NPC high incidence area. EBV nuclear antigen 1 (EBNA1) is the only latent protein consistently expressed in viral-associated tumors. The protein consists of 641 amino acids, including unique N-terminal(aa 1-89), internal glycine/alanine- rich repeat (GAR,aa 90-326) and COOH-terminal (aa 327－641). Based on the variation at amino acid 487, EBNA1 has been classified into five subtypes: P-ala (B95.8 prototype), P-thr, V-val, V-leu and V-pro

We demonstrate that using longer-wavelength driving light in high-order harmonic generation requires moderately ionized larger-density atoms to perfectly phase match the process, scaling conventional phase matching at low ionization to extremely high photon energies.

We demonstrate enhancement of high harmonic generation in the technologically significant 95 eV photon energy region by combining phase matching, quasi phase matching, and pulse compression in a single gas-filled waveguide. The waveguide geometry allows us to use argon gas as the generating medium, which also leads to enhanced emission due to its higher nonlinearity. The induced shock front due to laser pulse compression in the ionizing gas medium also generates an X-ray continuum at low pressure, with a spectrum corresponding to an isolated, 50 attosecond, X-ray pulse.

I will present work on hybrid fiber/bulk systems employing non-linear amplifiers to reach near and mid-IR wavelengths to obtain high peak and average powers, with