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We report on the nonlinear temporal compression of mJ energy pulses from a Ti:Sa chirped pulse amplifier system in a multipass cell filled with argon. The pulses are compressed from 30 fs down to 5.3 fs, corresponding to two optical cycles. The post-compressed beam exhibits excellent spatial quality and homogeneity. These results provide guidelines for optimizing the compressed pulse quality and further scaling of multipass-cell-based post-compression down to the single-cycle regime.

We report evidence for the first generation of XUV spectra from relativistic surface high-harmonic generation (SHHG) on plasma mirrors at a kilohertz repetition rate, emitted simultaneously with energetic electrons. SHHG spectra and electron angular distributions are measured as a function of the experimentally controlled plasma density gradient scale length Lg for three increasingly short and intense driving pulses: 24 fs and a0=1.1, 8 fs and a0=1.6, and finally 4 fs and a0≈2.1, where a0 is the peak vector potential normalized by mec/e with the elementary charge e, the electron rest mass me, and the vacuum light velocity c. For all driver pulses, we observe correlated relativistic SHHG and electron emission in the range Lg∈λ/20,λ/4, with an optimum gradient scale length of Lg≈λ/10. This universal optimal Lg-range is rationalized by deriving a direct intensity-independent link between the scale length Lg and an effective similarity parameter for relativistic laser-plasma interactions.

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In laser-wakefield acceleration, an ultra-intense laser pulse is focused into an underdense plasma to accelerate electrons to relativistic velocities. In most cases, the pulses consist of multiple optical cycles and the interaction is well described in the framework of the ponderomotive force where only the envelope of the laser has to be considered. But when using single-cycle pulses, the ponderomotive approximation breaks down, and the actual waveform of the laser has to be taken into account. In this paper, we use nearsingle-cycle laser pulses to drive a laser-wakefield accelerator. We observe variations of the electron beam pointing on the order of 10 mrad in the polarization direction, as well as 30% variations of the beam charge, locked to the value of the controlled laser carrier-envelope phase, in both nitrogen and helium plasma. Those findings are explained through particle-in-cell simulations indicating that low-emittance, ultrashort electron bunches are periodically injected off-axis by the transversally oscillating bubble associated with the slipping carrier-envelope phase.

We report on the first observation and control of carrier-envelope phase effects in Laser Wakefield Acceleration. These effects imply the breakdown of the cycle-averaged ponderomotive approximation and are explained through highly localized off-axis electron injection.

We report on carrier-envelope phase (CEP) effects on the emission of high-order harmonics and electron beams from plasma mirrors driven by relativistic-intensity near-single-cycle laser pulses at 1 kHz repetition rate.

We report on cross-polarised wave generation in multi-pass cells at the milli-Joule level. Backed by simulations, results indicate 103 contrast enhancement, high spatio-temporal beam quality, and a record internal conversion efficiency of 50%.