The enhancement effect of a microstructured surface on laser absorption and characteristic K alpha emission has been investigated by measuring K-shell emission from titanium (Ti) targets irradiated with high-intensity (similar to 1020 W cm-2), subpicosecond (500 fs) laser pulses. The experimental results indicate a modest enhancement (1.6x) of K alpha emission from microstructured targets compared to flat foils, but with a similar intensity and profile of He alpha and Li-like satellites. Particle-in-cell (PIC) simulations are implemented to further understand the underlying physical processes in the laser interaction with both targets, interpreting the mechanisms responsible for the K alpha enhancement. The reasons for the lower-than-expected enhancement of K alpha emission are discussed. The rapid heating of the bulk plasma might result in the premature shutdown of K alpha emission before the thermalization of hot electrons or even the end of laser pulses, suggesting that the use of K alpha emission as a diagnostic of the hot-electron yield or relaxation could lead to a misinterpretation.

In order to accurately probe high energy density matter states, it is vital to create powerful x-ray backlighters. One approach to create such x-ray sources is based on the usage of short-pulse, high-energy lasers, which greatly benefits from an optimization of the laser target coupling. Here, the spectral and temporal x-ray emission profiles of structured silicon targets with micron-sized spikes on the front surface are studied at laser intensities of 1017 W cm−2. The laser pulse length is varied between 1 and 20 ps with an energy of up to 1 kJ. The structured targets show an up to 13× enhancement of silicon Heα emission compared to flat foils with a well-defined, sharp emission pulse profile. Furthermore, the performance of the microstructured targets is compared to targets with a CH shield as well as foils irradiated with a UV prepulse.

Neutrons are a valuable tool for non-destructive material investigation as their interaction cross sections with matter are isotope sensitive and can be used complementary to x-rays. So far, most neutron applications have been limited to large-scale facilities such as nuclear research reactors, spallation sources, and accelerator-driven neutron sources. Here we show the design and optimization of a laser-driven neutron source in the epi-thermal and thermal energy range, which is used for non-invasive material analysis. Neutron resonance spectroscopy, neutron radiography, and neutron resonance imaging with moderated neutrons are demonstrated for investigating samples in terms of isotope composition and thickness. The experimental results encourage applications in non-destructive and isotope-sensitive material analysis and pave the way for compact laser-driven neutron sources with high application potential.

Targets with microstructured front surfaces have shown great potential in improving high-intensity laser-matter interaction. We present cone-shaped microstructures made out of silicon and titanium created by ultrashort laser pulse processing with different characteristics. In addition, we illustrate a process chain based on moulding to recreate the laser-processed samples out of polydimethylsiloxane, polystyrol and copper. With all described methods, samples of large sizes can be manufactured, therefore allowing time-efficient, cost-reduced and reliable ways to fabricate large quantities of identical targets.

High backlighter brightness is important to maximize the number of detected photons in radiography experiments and to minimize the background while back-lighting high-energy-density plasmas with strong self-emission. Several different configurations were tested to improve the brightness of the Si He-alpha x-ray line emission at a photon energy of 1865 eV from high-energy (> 1 kJ), short-pulse (-20 ps), laser-driven backlighter targets. The emission from low-density SiO2 foam targets, the effects of a laser prepulse, and Si targets with a CH "shield " that form a small cavity were compared to solid-density, flat Si targets. The CH "shield " targets showed the best performance with a > 5ximprovement in time-integrated emission and an x-ray pulse duration of similar to 25 ps with no measurable spectral shift of the Si He-alpha emission line. A conversion efficiency from laser light into Si He alpha photons on the order of 1 x 10(-5) was inferred from the data.

Numerous experiments on laser-driven proton acceleration in the MeV range have been performed with a large variety of laser parameters since its discovery around the year 2000. Both experiments and simulations have revealed that protons are accelerated up to a maximum cut-off energy during this process. Several attempts have been made to find a universal model for laser proton acceleration in the target normal sheath acceleration regime. While these models can qualitatively explain most experimental findings, they can hardly be used as predictive models, for example, for the energy cut-off of accelerated protons, as many of the underlying parameters are often unknown. Here we analyze experiments on laser proton acceleration in which scans of laser and target parameters were performed. We derive empirical scaling laws from these parameter scans and combine them in a scaling law for the proton energy cut-off that incorporates the laser pulse energy, the laser pulse duration, the focal spot radius, and the target thickness. Using these scaling laws, we give examples for predicting the proton energy cut-off and conversion efficiency for state-of-the-art laser systems.

We present the usage of two-layer targets with laser-illuminated front-side microstructures for x-ray backlighter applications. The targets consisted of a silicon front layer and copper back side layer. The structured layer was irradiated by the 500-fs PHELIX laser with an intensity above 10^{20}Wcm^{-2}. The total emission and one-dimensional extent of the copper Kα x-ray emission as well as a wide spectral range between 7.9 and 9.0 keV were recorded with an array of crystal spectrometers. The measurements show that the front-side modifications of the silicon in the form of conical microstructures maintain the same peak brightness of the Kα emission as flat copper foils while suppressing the thermal emission background significantly. The observed Kα source sizes can be influenced by tilting the conical microstructures with respect to the laser axis. Overall, the recorded copper Kα photon yields were in the range of 10^{11}sr^{-1}, demonstrating the suitability of these targets for probing applications without subjecting the probed material to additional heating from thermal line emission.

Laser-based particle accelerators have been an active field of research for over two decades moving from laser systems capable of one shot every hour to systems able to deliver repetition rates in the Hz regime. Based on the advancements in laser technology, the corresponding detection methods need to develop from single to multiple use with high readout speed. Here, we present an online compact tracker of particles using scintillators with nine resolvable energy levels and a spatial resolution of 3.6 × 3.6 mm2 over the whole active area. This paper describes the design and construction of the detector, which is based on pixellated scintillators embedded inside an absorber matrix. The scintillator pixels are fiberoptically coupled to a camera system for online readout and analysis. Calibration with a radioactive source and first experimental data measuring laser accelerated ions at the PHELIX laser at GSI, Darmstadt, Germany, are presented and discussed.

With the phasing out of many research reactors over the upcoming years, a shortcoming of small and medium sized neutron sources is to be expected. Laser-driven neutron sources have the potential to fill this void, with enormous progress being made in laser technology over the past years. Upcoming petawatt lasers with high repetition rates up to 10 Hz promise a tremendous increase in neutron flux. In this paper, a setup is developed and optimized to conduct neutron resonance spectroscopy at a laser-driven neutron source. This setup is then evaluated at an experimental campaign at the PHELIX laser system. Laser intensities up to 1021 W/cm² with a ns pre-pulse contrast of 10-7 were used for ion acceleration, resulting in (1.8±0.7)×108 N/sr per pulse corresponding to (2.3±1.0)×109 N in a 4 π equivalent. These pulses were moderated, collimated and investigated via the time of flight method in order to characterize the thermal neutron spectrum as well as the signal to noise ratio.

The production of intense x-ray and particle sources is one of the most remarkable aspects of high energy laser interaction with a solid target. Wide application of these laser-driven secondary sources requires a high yield, which is partially limited by the amount of laser energy absorbed by the target. Here, we report on the enhancement of laser absorption and x-ray and particle flux by target surface modifications. In comparison to targets with flat front surfaces, our experiments show exceptional laser-to-target performance for our novel cone-shaped silicon microstructures. The structures are manufactured via laser-induced surface structuring. Spectral and spatial studies of reflectance and x-ray generation reveal significant increases of the silicon Kα line and a boost of the overall x-ray intensity, while the amount of reflected light decreases. Also, the proton and electron yields are enhanced, but both temperatures remain comparable to those of flat foil targets. We support the experimental findings with 2D particle in cell simulations to identify the mechanisms responsible for the strong enhancement. Our results demonstrate how custom surface structures can be used to engineer high power laser-plasma sources for future applications.

The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the interaction physics is explored numerically. Diffraction and speckle patterns are measured in the specularly reflected light in the cases of targets with regular groove and needle-like structures, respectively, highlighting the potential to use this as a diagnostic of the evolving plasma surface. It is shown, via ray-tracing and numerical modelling, that for a laser focal spot diameter smaller than the periodicity of the target structure, the reflected light patterns can potentially be used to diagnose the degree of plasma expansion, and by extension the local plasma temperature, at the focus of the intense laser light. The reflected patterns could also be used to diagnose the size of the laser focal spot during a high-intensity interaction when using a regular structure with known spacing.

We present a process to fabricate micro-structured thin silicon foils with highly light absorbing properties over a broad wavelength region based on short-pulse laser treatment. We employ this fascinating technique to the fabrication of targets for high-intensity laser-plasma experiments. A polished silicon wafer is processed with high-intensity femtosecond laser pulses resulting in conical spikes within the irradiated region. Height, distance, and shape of these spikes depend primarily on the number, energy, central wavelength and duration of the incident laser pulses, as well as the ambient medium. This method is of great value for the future development of target fabrication. The broad parameter base offers a huge selection regarding shape and dimensions of the resulting structure. It can be included in existing laser operations within the manufacturing chain while offering a high degree of customisability. Within the reach of higher repetition rates of high-power laser systems and an increased number of requested targets, this manufacturing method can be scaled while being cost efficient and easily adaptable.

Localizing text in images is an important step in a number of applications and fundamental for optical character recognition. While born-digital text localization might look similar to other complex tasks in this field, it has certain distinct characteristics. Our novel approach combines individual strengths of the commonly used methods: stroke width transform and extremal regions and combines them with a method based on edge-based morphologically growing. We present a parameter-free method with high flexibility to varying text sizes and colorful image elements. We evaluate our method on a novel image database of different retail prospects, containing textual product information. Our results show a higher f-score than competitive methods on that particular task.

Ultrashort laser pulses are used to create surface structures on thin ($25~\unicode[STIX]{x03BC}\text{m}$) silicon (Si) wafers. Scanning the wafer with a galvanometric mirror system creates large homogeneously structured areas. The variety of structure shapes that can be generated with this method is exemplified by the analysis of shape, height and distance of structures created in the ambient media air and isopropanol. A study of the correlation between structure height and remaining wafer thickness is presented. The comparatively easy manufacturing technique and the structure variety that allows for custom-tailored targets show great potential for high repetition rate ion acceleration experiments.

When using anonymous offline questionnaires for reviewing services or products it is often not guaranteed that a reviewer does this only once as intended. In this paper an applied combination of different features of handwritten characteristics and its fusion is presented to expose such manipulations. The presented approach covers the aspects of alignment normalization, segmentation, feature extraction, classification and fusion. Nine features from handwritten text, numbers and check-boxes are extracted and used to recognize hand-writer duplicates. The proposed method has been tested on a novel database containing pages of handwritten text produced by 1,734 writers. Furthermore we show that the unified biometric decision using a weighted sum combination rule can significantly improve writer identification performance even on low level features.