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Laser plasma-based particle accelerators attract great interest in fields where conventional accelerators reach limits based on size, cost or beam parameters. Despite the fact that particle in cell simulations have predicted several advantageous ion acceleration schemes, laser accelerators have not yet reached their full potential in producing simultaneous high-radiation doses at high particle energies. The most stringent limitation is the lack of a suitable high-repetition rate target that also provides a high degree of control of the plasma conditions required to access these advanced regimes. Here, we demonstrate that the interaction of petawatt-class laser pulses with a pre-formed micrometer-sized cryogenic hydrogen jet plasma overcomes these limitations enabling tailored density scans from the solid to the underdense regime. Our proof-of-concept experiment demonstrates that the near-critical plasma density profile produces proton energies of up to 80 MeV. Based on hydrodynamic and three-dimensional particle in cell simulations, transition between different acceleration schemes are shown, suggesting enhanced proton acceleration at the relativistic transparency front for the optimal case. Laser-produced plasma can be used for particle acceleration in different schemes. Here the authors demonstrate proton acceleration from the intense ultrashort laser pulse interaction with micron-sized cryogenic hydrogen jet.

Application experiments with laser plasma-based accelerators (LPA) for protons have to cope with the inherent fluctuations of the proton source. This creates a demand for non-destructive and online spectral characterization of the proton pulses, which are for application experiments mostly spectrally filtered and transported by a beamline. Here, we present a scintillator-based time-of-flight (ToF) beam monitoring system (BMS) for the recording of single-pulse proton energy spectra. The setup’s capabilities are showcased by characterizing the spectral stability for the transport of LPA protons for two beamline application cases. For the two beamline settings monitored, data of 122 and 144 proton pulses collected over multiple days were evaluated, respectively. A relative energy uncertainty of 5.5% (1 σ ) is reached for the ToF BMS, allowing for a Monte-Carlo based prediction of depth dose distributions, also used for the calibration of the device. Finally, online spectral monitoring combined with the prediction of the corresponding depth dose distribution in the irradiated samples is demonstrated to enhance applicability of plasma sources in dose-critical scenarios.

Due to the non-linear nature of relativistic laser induced plasma processes, the development of laser-plasma accelerators requires precise numerical modeling. Especially high intensity laser-solid interactions are sensitive to the temporal laser rising edge and the predictive capability of simulations suffers from incomplete information on the plasma state at the onset of the relativistic interaction. Experimental diagnostics utilizing ultra-fast optical backlighters can help to ease this challenge by providing temporally resolved inside into the plasma density evolution. We present the successful implementation of an off-harmonic optical probe laser setup to investigate the interaction of a high-intensity laser at 5.4 × 10 21 W/cm 2 peak intensity with a solid-density cylindrical cryogenic hydrogen jet target of 5 μ m diameter as a target test bed. The temporal synchronization of pump and probe laser, spectral filtering and spectrally resolved data of the parasitic plasma self-emission are discussed. The probing technique mitigates detector saturation by self-emission and allowed to record a temporal scan of shadowgraphy data revealing details of the target ionization and expansion dynamics that were so far not accessible for the given laser intensity. Plasma expansion speeds of up to ( 2.3 ± 0.4 ) × 10 7 m/s followed by full target transparency at 1.4 ps after the high intensity laser peak are observed. A three dimensional particle-in-cell simulation initiated with the diagnosed target pre-expansion at - 0.2 ps and post processed by ray tracing simulations supports the experimental observations and demonstrates the capability of time resolved optical diagnostics to provide quantitative input and feedback to the numerical treatment within the time frame of the relativistic laser-plasma interaction.

In ultra-short laser pulses, small changes in dispersion properties before the final focusing mirror can lead to severe pulse distortions around the focus and therefore to very different pulse properties at the point of laser–matter interaction, yielding unexpected interaction results. The mapping between far- and near-field laser properties intricately depends on the spatial and angular dispersion properties as well as the focal geometry. For a focused Gaussian laser pulse under the influence of angular, spatial and group-delay dispersion, we derive analytical expressions for its pulse-front tilt, duration and width from a fully analytic expression for its electric field in the time–space domain obtained with scalar diffraction theory. This expression is not only valid in and near the focus but also along the entire propagation distance from the focusing mirror to the focus. Expressions relating angular, spatial and group-delay dispersion before focusing at an off-axis parabola, where they are well measurable, to the respective values in the pulse’s focus are obtained by a ray tracing approach. Together, these formulas are used to show in example setups that the pulse-front tilts of lasers with small initial dispersion can become several tens of degrees larger in the vicinity of the focus while being small directly in the focus. The formulas derived here provide the analytical foundation for observations previously made in numerical experiments. By numerically simulating Gaussian pulse propagation and measuring properties of the pulse at distances several Rayleigh lengths off the focus, we verify the analytic expressions.

We report on the development of an ultrafast optical parametric amplifier front-end for the Petawatt High Energy Laser for heavy Ion eXperiments (PHELIX) and the Petawatt ENergy-Efficient Laser for Optical Plasma Experiments (PEnELOPE) facilities. This front-end delivers broadband and stable amplification up to 1 mJ per pulse while maintaining a high beam quality. Its implementation at PHELIX allowed one to bypass the front-end amplifier, which is known to be a source of pre-pulses. With the bypass, an amplified spontaneous emission contrast of $4.9\\times {10}^{-13}$ and a pre-pulse contrast of $6.2\\times {10}^{-11}$ could be realized. Due to its high stability, high beam quality and its versatile pump amplifier, the system offers an alternative for high-gain regenerative amplifiers in the front-end of various laser systems.

An improved moveable in vacuo XUV fluorescence detection system was employed for the laser cooling of bunched relativistic (β = 0.47) carbon ions at the Experimental Storage Ring (ESR) of GSI Helmholtzzentrum Darmstadt, Germany. Strongly Doppler boosted XUV fluorescence (∼90 nm) was emitted from the ions in a forward light cone after laser excitation of the 2s–2p transition (∼155 nm) by a new tunable pulsed UV laser system (257 nm). It was shown that the detected fluorescence strongly depends on the position of the detector around the bunched ion beam and on the delay (∼ns) between the ion bunches and the laser pulses. In addition, the fluorescence information could be directly combined with the revolution frequencies of the ions (and their longitudinal momentum spread), which were recorded using the Schottky resonator at the ESR. These fluorescence detection features are required for future laser cooling experiments at highly relativistic energies (up to γ∼ 13) and high intensities (up to 1011 particles) of ion beams in the new heavy ion synchrotron SIS100 at FAIR.

We present picosecond Yb:YAG and Yb:CaF2 regenerative laser amplifiers with ultra-high repetition rates in the MHz range. A maximum pulse energy of 40 μJ was obtained at 20 kHz while we achieved around 1 μJ at 1 MHz. We demonstrated a pulse duration of 2.1 ps for Yb:YAG and 4.8 ps for Yb:CaF2 when seeded by a mode-locked Yb:KGW fs-oscillator without pulse stretching or phase compensation.

We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 10 9 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (∅ 5 μm) and planar (20 μm × 2 μm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions.

BackgroundThis study analyzed the long-term survival after pathological complete response (pCR) with and without nodal metastases and associated recurrence following multimodal treatment of esophageal cancer. The recurrence pattern after pCR is of importance for different postoperative surveillance strategies.MethodsA cohort of 890 patients with esophageal cancer received neoadjuvant therapy followed by transthoracic esophagectomy. Only patients with pCR of the primary tumor with and without nodal metastasis were analyzed. A clinicopathological database was set up and completed with long-term follow up information on recurrent disease.ResultsThe specimen of 201 patients (23%) demonstrated pCR, 84% without (ypT0N0) and 16% with residual nodal disease (ypT0N+). For ypT0N0 patients, the 5-year overall survival was significantly higher than for patients with metastatic nodes (77% vs. 24%) (p < 0.0001). Sixty-eight percent of patients had no evidence of tumor recurrence, whereas 32% had proven relapse. For patients with and without tumor recurrence, 5-year survival rates were 14% and 93%, respectively (p < 0.0001). For patients with recurrent disease, median survival time was 27 for locoregional, 44 for distant, and 24 months for combined recurrence (p = 0.302). In the multivariable Cox-regression analysis, node-positive disease predicted both locoregional and metastatic recurrence.ConclusionsPathological CR offers long-term survival in patients without nodal metastases but outcome significantly deteriorates with the presence of nodal metastases. Follow-up recommendations may therefore be adopted in patients with pCR. Furthermore, “watch-and-wait” surveillance strategies with suspected clinical complete response have to be considered with caution.

The role of subcellular survivin compartmentalization in the biology and prognosis of prostate cancer is unclear. We therefore investigated subcellular localization of survivin in more than 3000 prostate cancer patients by quantitative immunohistochemistry and performed transcriptomics of 250 prostate cancer patients and healthy donors using publicly available datasets. Survivin (BIRC5) gene expression was increased in primary prostate cancers and metastases, but did not differ in recurrent vs non-recurrent prostate cancers. Survivin immunohistochemistry (IHC) staining was limited exclusively to the nucleus in 900 prostate cancers (40.0%), and accompanied by various levels of cytoplasmic positivity in 1338 tumors (59.4%). 0.5% of prostate cancers did not express survivin. Nuclear and cytoplasmic survivin staining intensities were strongly associated with each other, pT category, and higher Gleason scores. Cytoplasmic but not nuclear survivin staining correlated with high tumor cell proliferation in prostate cancers. Strong cytoplasmic survivin staining, but not nuclear staining predicted an unfavorable outcome in univariate analyses. Multivariate Cox regression analysis showed that survivin is not an independent prognostic marker. In conclusion, we provide evidence that survivin expression is increased in prostate cancers, especially in metastatic disease, resulting in higher aggressiveness and tumor progression. In addition, subcellular compartmentalization is an important aspect of survivin cancer biology, as only cytoplasmic, but not nuclear survivin accumulation is linked to biological aggressiveness and prognosis of prostate cancers.