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The absolute response of a real-time proton detector, composed of a microchannel plate (MCP) assembly, an imaging lens, and a charge-coupled device (CCD) camera, is calibrated for the spectral characterization of laser-accelerated protons, using a Thomson parabola spectrometer (TPS). A slotted CR-39 plate was used as an absolute particle-counting detector in the TPS, simultaneously with the MCP–CCD detector to obtain a calibration factor (count/proton). In order to obtain the calibration factor as a function of proton energy for a wide range of proton numbers, the absolute response was investigated for different operation parameters of the MCP–CCD detector, such as MCP voltage, phosphor voltage, and CCD gain. A theoretical calculation for the net response of the MCP was in good agreement with the calibrated response of the MCP–CCD detector, and allows us to extend the response to higher proton energies. The response varies in two orders of magnitude, showing an exponential increase with the MCP voltage and almost linear increase with the phosphor voltage and the CCD gain. The calibrated detector enabled characterization of a proton energy spectrum in a wide dynamic range of proton numbers. Moreover, two MCP assemblies having different structures of MCP, phosphor screen, and optical output window have been calibrated, and the difference in the absolute response was highlighted. The highly-sensitive detector operated with maximum values of the parameters enables measuring a single proton particle and evaluating an absolute spectrum at high proton energies in a single laser shot. The absolute calibrations can be applied for the spectral measurement of protons using different operating voltages and gains for optimized response in a large range of proton energy and number. [ABSTRACT FROM AUTHOR]

In all-optical Compton scattering driven by a multi-petawatt laser, it is critical to have accurate spatiotemporal synchronization between the ultrarelativistic electron bunch and the ultrahigh-intensity laser beam. Such a synchronization was realized by using two complementary optical setups. The first setup, used for the initial synchronization, recorded the spatial interferogram between the two femtosecond lasers used for a GeV electron beam production and an ultrahigh scattering laser beam. The second one, consisting of spatial and spectral interferometers, measured the time delay between the two laser beams in the range of 0–200 fs in real time. These monitoring systems played an essential role in conducting Compton scattering experiments. [ABSTRACT FROM AUTHOR]

Featured Application: Compact electron accelerators, Compact synchrotron source, Radiography. Laser wakefield electron acceleration (LWFA) is an emerging technology for the next generation of electron accelerators. As intense laser technology has rapidly developed, LWFA has overcome its limitations and has proven its possibilities to facilitate compact high-energy electron beams. Since high-power lasers reach peak power beyond petawatts (PW), LWFA has a new chance to explore the multi-GeV energy regime. In this article, we review the recent development of multi-GeV electron acceleration with PW lasers and discuss the limitations and perspectives of the LWFA with high-power lasers. [ABSTRACT FROM AUTHOR]

We present a proof of principle for onsite calibration of a radiochromic film (EBT3) using CR-39 as an absolute proton-counting detector and laser-accelerated protons as a calibration source. A special detector assembly composed of aluminum range filters, an EBT3 film, and a CR-39 detector is used to expose the EBT3 film with protons in an energy range of 3.65 MeV–5.85 MeV. In our design, the proton beam is divided into small beamlets and their projection images are taken on the EBT3 film and the CR-39 detector by maintaining a certain distance between the two detectors. Owing to the geometrical factor of the configuration and scattering inside the EBT3, the areal number density of protons was kept below the saturation level of the CR-39 detector. We also present a method to relate the number of protons detected on the CR-39 in a narrow energy range to protons with a broad energy spectrum that contribute to the dose deposited in the EBT3 film. The energy spectrum of protons emitted along the target normal direction is simultaneously measured using another CR-39 detector installed in a Thomson parabola spectrometer. The calibration curves for the EBT3 film were obtained in the optical density range of 0.01–0.25 for low dose values of 0.1 Gy–3.0 Gy. Our results are in good agreement with the calibrations of the EBT3 film that are traditionally carried out using conventional accelerators. The method presented here can be further extended for onsite calibration of radiochromic films of other types and for a higher range of dose values. [ABSTRACT FROM AUTHOR]

Recent ultra-short high-power lasers can provide ultra-high laser intensity over 1022 W/cm2. Laser fields of such extreme strengths instantaneously turn matter into plasma, which exhibits relativistic collective dynamics, thereby leading to unprecedented physical systems with potential breakthrough applications. In this article, we introduce the basic concepts and trace the progress in ultra-high intensity laser development and relativistic laser-plasma interactions, including laser-driven charged particle acceleration. [ABSTRACT FROM AUTHOR]

We demonstrated single-shot high-numerical-aperture coherent diffraction imaging (CDI) with a diffraction-limited resolution using table-top x-ray laser at 13.9 nm. In order to achieve the diffraction-limited resolution, a nonlinear phase variation was introduced in a sample so that an asymmetric diffraction pattern with clear visibility could be extended to high spatial frequencies. From the diffraction signal, the sample image was successfully reconstructed with a resolution of 22 nm, which is close to the diffraction-limited resolution of 21 nm, using the phase retrieval procedure. The model calculation and simulations, performed to verify the experimental results, showed that the implementation of the nonlinear phase variation in the sample enhanced the resolution by a factor of about two, as compared to the case of a pure absorption sample. In addition, we examined the CDI with phase controllers introducing nonlinear phase variation illuminated by a table-top femtosecond Kr x-ray laser pulse at 32.8 nm that produced an asymmetric diffraction pattern extended to high spatial frequencies. [ABSTRACT FROM AUTHOR]

Advanced laser wakefield accelerators offer electron beams which could be useful for many applications. However, the problem of stabilizing the electron beam parameters has not been resolved yet. Here, we report the generation of a relativistic electron beam with a stabilized pointing angle of 2 mrad (rms). This was achieved by using asymmetric nonrelativistic laser pulses interacting with low-density helium gas. In such a weakly-nonlinear regime, symmetric laser pulses were neither able to generate reproducible nor stable electron beams. Thus, we propose asymmetric laser pulses for generating electron beams having stable and small pointing angles from laser–plasma accelerators. [ABSTRACT FROM AUTHOR]