Optical steering of electron beam in laser plasma accelerators.

Using a Dazzler system and tilting a compressor grating, we provide an effective way of using the laser group delay dispersion to continuously steer the electron beam accelerated by an asymmetric laser wakefield. The deviation angle of the electron beam was the same as that of the angularly chirped laser pulse from its initial optical axis, which is determined by the laser pulse-front-tilt (PFT). This method can be utilized to continuously control over the pointing direction of electron bunches to the requisite trajectories, especially for practical applications in highly sensitive alignment devices such as electron-positron colliders or undulators. Additionally, we investigate the effect of PFT on the properties of the electron beam.

Highly efficient generation of 0.2 mJ terahertz pulses in lithium niobate at room temperature with sub-50 fs chirped Ti:sapphire laser pulses.

We demonstrate generation of 0.2 mJ terahertz (THz) pulses in lithium niobate driven by Ti:sapphire laser pulses at room temperature. Employing tilted pulse front technique, the 800 nm-to-THz energy conversion efficiency has been optimized to 0.3% through chirping the sub-50 fs pump laser pulses to overcome multi-photon absorption and to extend effective interaction length for phase matching. Our approach paves the way for mJ-level THz generation via optical rectification using existing Ti:sapphire laser systems which can deliver Joule-level pulse energy with sub-50 fs pulse duration.

Backward terahertz radiation from intense laser-solid interactions.

We report a systematic study on backward terahertz (THz) radiation generation from laser-solid interactions by changing a variety of laser/plasma parameters. We demonstrate a high-energy (with an energy flux density reaching 80 µJ/sr), broadband (>10 THz) plasma-based radiation source. The radiation energy is mainly distributed either in the >10 THz or <3 THz regions. A radial surface current formed by the lateral transport of low-energy electrons (LEE) is believed to be responsible for the radiation in the high-THz region (>10 THz), while high-energy surface fast electrons (SFE) accelerated along the target surface mainly contribute to lower frequency (<3 THz) radiation. The unifying explanation could be applied to backward THz radiation generation from solid targets with presence of relative small preplasmas.

Demonstration of Coherent Terahertz Transition Radiation from Relativistic Laser-Solid Interactions.

Coherent transition radiation in the terahertz (THz) region with energies of sub-mJ/pulse has been demonstrated by relativistic laser-driven electron beams crossing the solid-vacuum boundary. Targets including mass-limited foils and layered metal-plastic targets are used to verify the radiation mechanism and characterize the radiation properties. Observations of THz emissions as a function of target parameters agree well with the formation-zone and diffraction model of transition radiation. Particle-in-cell simulations also well reproduce the observed characteristics of THz emissions. The present THz transition radiation enables not only a potential tabletop brilliant THz source, but also a novel noninvasive diagnostic for fast electron generation and transport in laser-plasma interactions.

Role of resonance absorption in terahertz radiation generation from solid targets.

The interaction of 100-fs laser pulses with solid targets at laser intensities 10(16)-10(18)W/cm(2) has been investigated experimentally by simultaneous measurements of terahertz (THz) and second harmonic signals. THz yield at the front side of the target, which rises from the self-organized transient electron currents along the target surface, is found scaling linearly with the laser intensity basically. Measurements of specularly reflected light spectrum show clear evidence of resonance absorption. The positive effects of resonance absorption on surface current and THz radiation generation have been confirmed by two-dimensional (2D) particle-in-cell (PIC) simulations and angular-dependent experiments, respectively.

Long lifetime air plasma channel generated by femtosecond laser pulse sequence.

Lifetime of laser plasma channel is significantly prolonged using femtosecond laser pulse sequence, which is generated from a chirped pulse amplification laser system with pure multi-pass amplification chain. Time-resolved fluorescence images and electrical conductivity measurement are used to characterize the lifetime of the plasma channel. Prolongation of plasma channel lifetime up to microsecond level is observed using the pulse sequence.

Isolated cryptococcal osteomyelitis of the ulna in an immunocompetent patient: A case report.

BACKGROUND: Cryptococcal osteomyelitis is a bone infection caused by cryptococcus. As an opportunistic infection, bone cryptococcosis usually occurs in patients with immunodeficiency diseases or in those undergoing immunosuppressive therapy and often displays characteristics of disseminated disease. Isolated cryptococcal osteomyelitis is extremely unusual in immunocompetent person. The pathogenic fungus often invades vertebrae, femur, tibia, rib, clavicle, pelvis, and humerus, but the ulna is a rare target. CASE SUMMARY: A 79-year-old woman complaining of chronic pain, skin ulceration and a sinus on her right forearm was admitted, and soon after was diagnosed with cryptococcal osteomyelitis in the right ulna. Unexpectedly, she was also found to have apparently normal immunity. After treatment with antifungal therapy combined with surgery debridement, the patient's osteomyelitis healed with a satisfactory outcome. CONCLUSION: Although rare, cryptococcal osteomyelitis should be considered in the differential diagnosis of osteolytic lesions even in immunocompetent patients, and good outcomes can be expected if early definitive diagnosis and etiological treatment are established.

Highly efficient generation of GV/m-level terahertz pulses from intense femtosecond laser-foil interactions.

The terahertz radiation from ultraintense laser-produced plasmas has aroused increasing attention recently as a promising approach toward strong terahertz sources. Here, we present the highly efficient production of millijoule-level terahertz pulses, from the rear side of a metal foil irradiated by a 10-TW femtosecond laser pulse. By characterizing the terahertz and electron emission in combination with particle-in-cell simulations, the physical reasons behind the efficient terahertz generation are discussed. The resulting focused terahertz electric field strength reaches over 2 GV/m, which is justified by experiments on terahertz strong-field-driven nonlinearity in semiconductors.

Two-dimensional monitoring of a laser-solid x-ray source spot via penumbral coded aperture imaging technique.

The uncertainties of spot size and position need to be clarified for x-ray sources as they can affect the detecting precision of the x-ray probe beam in applications such as radiography. In particular, for laser-driven x-ray sources, they would be more significant as they influence the inevitable fluctuation of the driving laser pulses. Here, we have employed the penumberal coded aperture imaging technique to diagnose the two-dimensional spatial distribution of an x-ray emission source spot generated from a Cu solid target irradiated by an intense laser pulse. Taking advantage of the high detection efficiency and high spatial resolution of this technique, the x-ray source spot is characterized with a relative error of ∼5% in the full width at half maximum of the intensity profile in a single-shot mode for general laser parameters, which makes it possible to reveal the information of the unfixed spot size and position precisely. Our results show the necessity and feasibility of monitoring the spot of these novel laser-driven x-ray sources via the penumbral coded aperture imaging technique.

Enhanced Kα output of Ar and Kr using size optimized cluster target irradiated by high-contrast laser pulses.

We observed that increasing the clusters size and laser pulse contrast can enhance the X-ray flux emitted by femtosecond-laser-driven-cluster plasma. By focusing a high contrast laser (10(-10)) on large argon clusters, high flux Kα-like X-rays (around 2.96 keV) is generated with a total flux of 2.5 × 10(11) photons/J in 4π and a conversion efficiency of 1.2 × 10-4. In the case of large Kr clusters, the best total flux for L-shell X-rays is 5.3 × 1011 photons/J with a conversion efficiency of 1.3 × 10-4 and, for the Kα X-ray (12.7 keV), it is 8 × 10(8) photons/J with a conversion efficiency of 1.6 × 10-6. Using this X-ray source, a single-shot high-performance X-ray imaging is demonstrated.

Broadband supercontinuum generation in air using tightly focused femtosecond laser pulses.

Supercontinuum generation in air using tightly focused femtosecond laser pulses was investigated experimentally. Broadband white-light emission covering the whole visible spectral region was generated. Spectral broadening extended only to the blue side of the fundamental frequency due to the phase modulation induced by the strong ionization of air. Numerical simulation was also performed to confirm the spectral broadening mechanism. A constant UV cutoff wavelength close to 400 nm was observed in the supercontinuum spectrum. This phenomenon indicated that intensity clamping still plays a role in tight focusing geometry.

Tightly focused femtosecond laser pulse in air: from filamentation to breakdown.

The propagation of tightly focused femtosecond laser pulse with numerical aperture of 0.12 in air is investigated experimentally. The formation and evolution of the filament bunch are recorded by time-resolved shadowgraph with laser energy from 2.4 mJ to 47 mJ. The distribution of electron density in breakdown area is retrieved using Nomarski interferometer. It is found that intensity clamping during filamentation effect still play a role even under strong external focusing. The electron density in some interaction zones is higher than 3 × 10(19) cm(-3), which indicates that each air molecule there is ionized.

K-shell x-ray emission enhancement via self-guided propagation of intense laser pulses in Ar clusters.

K-shell x-ray at about 3 keV emitted from Ar clusters irradiated by 110 mJ 55 fs intense laser pulses is studied. The x-ray flux is optimized by moving the nozzle away from the focus of the laser pulse. The total flux of K-shell x-ray photons in 4pi reaches a maximum of 4.5x10(9) photons/shot with a conversion efficiency of 2.5x10(-5) when the nozzle displacement is 2 mm and a long plasma channel is observed by a probe beam.

Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence.

A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60-80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions.

Allotransplantation of cryopreserved prepubertal mouse ovaries restored puberty and fertility without affecting methylation profile of Snrpn-DMR.

OBJECTIVE: To evaluate the genetic safety of vitrification on the methylation imprints and the development and fertility potential of prepubertal mouse ovaries. DESIGN: Experimental animal study. SETTING: University-based fertility center. ANIMAL(S): Institute of Cancer Research (ICR) 10-day-old female mice, 10-week-old adult female mice, and 12-week-old adult male mice. INTERVENTION(S): Vitrification of juvenile mouse ovaries was performed using ED20 and EG5.5/30 solutions followed by retrieval of fresh and vitrified-warmed germinal vesicle (GV) oocytes for Snrpn differentially methylated regions (DMR) methylation analyses, collection of mature oocytes from superovulated ovarian grafts, in vitro fertility(IVF), and early embryonic development after heterotopic allotransplantation. MAIN OUTCOME MEASURE(S): Analysis of methylation status of Snrpn-DMR, percentage of fertilization, and blastocysts formation. RESULT(S): Methylation status of Snrpn-DMR from vitrified-warmed GV oocytes did not show significant alteration compared with that of controls, although a significant reduction of viable oocytes was observed. Puberty as well as endocrine function was restored, and no significant difference was shown in number of follicles, percentage of mice retaining fertility, and blastocyst formation among three groups. CONCLUSION(S): Our study proved that vitrification of prepubertal mouse ovaries did not alter the methylation profile of Snrpn-DMR and subsequent allotransplantation; IVF could restore the development and fertility potential.

Effects of laser-plasma interactions on terahertz radiation from solid targets irradiated by ultrashort intense laser pulses.

Interactions of 100-fs laser pulses with solid targets at intensities of 10(18) W/cm(2) and resultant terahertz (THz) radiation are studied under different laser contrast ratio conditions. THz emission is measured in the specular reflection direction, which appears to decrease as the laser contrast ratio varies from 10(-8) to 10(-6). Correspondingly, the frequency spectra of the reflected light are observed changing from second harmonic dominant, three-halves harmonic dominant, to vanishing of both harmonics. Two-dimensional particle-in-cell simulation also suggests that this observation is correlated with the plasma density scale length change. The results demonstrate that the THz emission is closely related to the laser-plasma interaction processes. The emission is strong when resonance absorption is a key feature of the interaction, and becomes much weaker when parametric instabilities dominate.