We demonstrate a laser wakefield accelerator with a novel electron injection scheme resulting in enhanced stability, reproducibility, and ease of use. In order to inject electrons into the accelerating phase of the plasma wave, a sharp downward density transition is employed. Prior to ionization by the laser pulse this transition is formed by a shock front induced by a knife edge inserted into a supersonic gas jet. With laser pulses of 8 fs duration and with only 65 mJ energy on target, the accelerator produces a monoenergetic electron beam with tunable energy between 15 and 25 MeV and on average 3.3 pC charge per electron bunch. The shock-front injector is a simple and powerful new tool to enhance the reproducibility of laser-driven electron accelerators, is easily adapted to different laser parameters, and should therefore allow scaling to the energy range of several hundred MeV.
Despite the central role of light absorption and the subsequent generation of free charge carriers in organic and hybrid organicÀinorganic photovoltaics, the precise process of this initial photoconversion is still debated. We employ a novel broadband (UVÀVisÀNIR) transient absorption spectroscopy setup to probe charge generation and recombination in the thin films of the recently suggested hybrid material combination poly(3-hexylthiophene)/silicon (P3HT/Si) with 40 fs time resolution. Our approach allows for monitoring the time evolution of the relevant transient species under various excitation intensities and excitation wavelengths. Both in regioregular (RR) and regiorandom (RRa) P3HT, we observe an instant (<40 fs) creation of singlet excitons, which subsequently dissociate to form polarons in 140 fs. The quantum yield of polaron formation through dissociation of delocalized excitons is significantly enhanced by adding Si as an electron acceptor, revealing ultrafast electron transfer from P3HT to Si. P3HT/Si films with aggregated RR-P3HT are found to provide free charge carriers in planar as well as in bulk heterojunctions, and losses are due to nongeminate recombination. In contrast for RRa-P3HT/Si, geminate recombination of bound carriers is observed as the dominant loss mechanism. Site-selective excitation by variation of pump wavelength uncovers an energy transfer from P3HT coils to aggregates with a 1/e transfer time of 3 ps and reveals a factor of 2 more efficient polaron formation using aggregated RR-P3HT compared to disordered RRa-P3HT. Therefore, we find that polymer structural order rather than excess energy is the key criterion for free charge generation in hybrid P3HT/Si solar cells.
We present a two-stage noncollinear optical parametric chirped-pulse amplification system that generates 7.9 fs pulses containing 130 mJ of energy at an 805 nm central wavelength and 10 Hz repetition rate. These 16 TW light pulses are compressed to within 5% of their Fourier limit and are carefully characterized by the use of home-built pulse diagnostics. The contrast ratio before the main pulse has been measured as 10(-4), 10(-8), and 10(-11) at t=-3.3 ps, t=-5 ps, and t=-30 ps, respectively. This source allows for experiments in a regime of relativistic light-matter interactions and attosecond science.
We report on an electron accelerator based on few-cycle (8 fs full width at half maximum) laser pulses, with only 40 mJ energy per pulse, which constitutes a previously unexplored parameter range in laser-driven electron acceleration. The produced electron spectra are monoenergetic in the tens-of-MeV range and virtually free of low-energy electrons with thermal spectrum. The electron beam has a typical divergence of 5-10 mrad. The accelerator is routinely operated at 10 Hz and constitutes a promising source for several applications. Scalability of the few-cycle driver in repetition rate and energy implies that the present work also represents a step towards user friendly laser-based accelerators.
The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 10 20 W/cm 2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-fielddriven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.The development and proliferation of intense lasers with sub-two optical-cycle duration during the past decade has allowed to create the tools and techniques for the observation and control of electronic motions in all forms of matter; a field nowadays known as attosecond physics 1 . These techniques have meanwhile provided direct time-domain access to a wide range of electron phenomena with a sub-fs resolution, such as miniscule delays in photo-emission timing 2,3 , charge migration in molecules 4, 5 and solids 6,7 , as well as collective electron motion in extreme laser-plasma interactions 8 . Powerful few-cycle laser pulses have traditionally been produced via chirped-pulse amplification (CPA) in titanium-doped sapphire (Ti:Sa) in conjunction with spectral broadening in gas-filled hollow-core fibres (HCF) 9 . CPA-based lasers have achieved peak powers beyond 1 PW, but only with pulse durations extending to about ten optical cycles or longer 10,11 . Spectral broadening in HCFs provides octave-spanning spectra, but the approach is still limited to pulses with a few millijoules in energy 12,13 . Due to these restrictions few-cycle-driven attosecond sources based on high-harmonic generation (HHG) in gas targets generally suffer from a low intensity, constituting a major limitation to pushing the frontiers of the field. Upscaling few-cycle-driven HHG to higher driving pulse energies [14][15][16] allows the generation of intense isolated attosecond pulses for time-resolved nonlinear optics experiments in the extreme-ultraviolet (XUV) spectral
Inhibition of prostate smooth muscle contraction is an important strategy for medical treatment of lower urinary tract symptoms (LUTS). Besides α1-adrenoceptors, prostate smooth muscle contraction is induced by activation of thromboxane (TXA2) receptors (TXA2-R). Here, we examined the effects of the TXA2-R antagonist picotamide on contraction of human prostate tissue. Prostate tissues were obtained from radical prostatectomy. The effects of picotamide (300 μM), L-665,240 (3 μM), and seratrodast (3 μM) on U46619-, electric field stimulation- (EFS-), phenylephrine-, and norepinephrine-induced contractions were studied in organ baths. Expression of TXA2-R and TXA2 synthase (TXS) was examined by fluorescence stainings. Picotamide, seratrodast, and L-655,240 inhibited concentration-dependent contractions induced by the TXA2 analog U46619. Picotamide, but not seratrodast or L-655,240, inhibited frequency-dependent contractions induced by EFS. Picotamide inhibited concentration-dependent contractions induced by norepinephrine or by the selective α1-adrenoceptor agonist phenylephrine. In prostate strips, where only submaximal contraction by a low dose of phenylephrine was induced, application of U46619 raised tone to maximum phenylephrine-induced tension. Immunoreactivity for TXA2-R and TXS was observed in the stroma and in epithelial cells of glands. Colocalization of both immunoreactivites was observed with the smooth muscle markers calponin and α-smooth muscle actin, with the epithelial marker pan-cytokeratin, and with prostate-specific antigen in the stroma and glands. The receptor antagonist picotamide inhibits α1-adrenergic, TXA2-mediated, and EFS-induced contractions in the human prostate. To the best of our knowledge, this is the first antagonist able to inhibit two different contraction systems in the prostate.
Hybrid organic-inorganic solar cells from poly(3-hexylthiophene) (P3HT) and freestanding silicon nanocrystals (Si-ncs) combine the advantages of siliconbased photovoltaics with the cost-efficient solution processing technique. At present, the microwave-plasma synthesis of Si-ncs that allows for a future upscaling to industrial demands is at the expense of the Si-nc surface quality and the number of charge-trapping defects. Here, we present an enhancement of the solar cell performance by identifying the major factors which are limiting the device efficiency. With the help of low-cost post-growth treatments of the Si-ncs and the optimization of various device parameters, P3HT:Si-ncs bulk heterojunction solar cells with an efficiency up to 1.1 % are achieved. In particular, etching of the Si-ncs with hydrofluoric acid to remove the surface oxide shells and surface defects has a strong impact on the solar cell performance. An intermediate Si weight ratio of around 60 % is found to lead to the highest current densities. For Si-ncs with very small diameters, an additional enhancement of the open circuit voltage was observed. Moreover, we show that the structural order of P3HT has a strong influence on the efficiency, which can be explained by an improved charge carrier separation at the P3HT/Si-ncs interface in combination with an enhanced charge transport in the P3HT phase.
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