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We have previously shown that laser light can be upshifted to higher frequencies by its reflection off relativistically moving mirrors in plasma. These mirrors were generated with ultra-high intensity laser pulses. However, the laser light which was reflected off the mirrors had relatively low intensity. We show via simulations that even high intensity light can be reflected off the mirrors and that this can generate relativistically upshifted harmonics. [ABSTRACT FROM AUTHOR]

The temporal contrast of an ultrahigh-intensity laser is a crucial parameter for laser plasma experiments. We have developed a multichannel cross-correlator (MCCC) for single-shot measurements of the temporal contrast in a high-power laser system. The MCCC is based on third-order cross-correlation, and has four channels and independent optical delay lines. We have experimentally demonstrated that the MCCC system achieves a high dynamic range of ∼1012 and a large temporal window of ∼1 ns. Moreover, we were able to measure the shot-to-shot fluctuations of a short-prepulse intensity at −26 ps and long-pulse (amplified spontaneous emission, ASE) intensities at −30, −450, and −950 ps before the arrival of the main pulse at the interaction point. [ABSTRACT FROM AUTHOR]

A new regime of relativistic high-order harmonic generation has been discovered (Pirozhkov 2012 Phys. Rev. Lett. 108 135004). Multi-terawatt relativistic-irradiance (>1018 W cm−2) femtosecond (∼30–50 fs) lasers focused to underdense (few × 1019 cm−3) plasma formed in gas jet targets produce comb-like spectra with hundreds of even and odd harmonic orders reaching the photon energy of 360 eV, including the ‘water window’ spectral range. Harmonics are generated either by linearly or circularly polarized pulses from the J-KAREN (KPSI, JAEA) and Astra Gemini (CLF, RAL, UK) lasers. The photon number scalability has been demonstrated with a 120 TW laser, producing 40 μJ sr−1 per harmonic at 120 eV. The experimental results are explained using particle-in-cell simulations and catastrophe theory. A new mechanism of harmonic generation by sharp, structurally stable, oscillating electron spikes at the joint of the boundaries of the wake and bow waves excited by a laser pulse is introduced. In this paper, detailed descriptions of the experiments, simulations and model are provided and new features are shown, including data obtained with a two-channel spectrograph, harmonic generation by circularly polarized laser pulses and angular distribution. [ABSTRACT FROM AUTHOR]

External magnetic devices have been successfully tested to control the divergence and pointing stability of subrelativistic electron beams accelerated by ultrashort laser pulses in a nitrogen plasma (electron density of ∼1019 cm−3). Different configurations of the magnetic devices have been studied, and their effects are discussed in detail. The analysis is also supported by the results of ray-tracing simulations using the first-order trajectory equation in the magnetic field configurations. This simple method of improving beam stability will be particularly useful for applying laser-generated ultrashort electron beams to high-dose radiobiological studies. [ABSTRACT FROM AUTHOR]