The constant increase of peak energy on high-intensity lasers necessitates the combined control of the laser pulse (with pulse shapers for temporal characterization) and the wavefront (with deformable mirrors for spatial characterization). Focusing the beam on the target creates space time couplings that were typically neglected until now. We have developed a solution that provides direct, spectrally-resolved wavefront measurements to characterize and quickly diminish those couplings. We will present concrete results on beamlines, highlighting the interest of a high spectral and spatial resolution system. Its simplicity of use will be demonstrated using the quick alignment of compressor gratings as an example.
We report temporal coherence measurement of solid-target plasma-based soft X-ray laser (XRL) in amplified spontaneous emission (ASE) mode. By changing the XRL pumping angle, we generate lasing at two-times higher electron density than the routine condition. A relatively shorter coherence time at a higher pumping angle indicates a clear spectral signature of higher electron density in the gain region. We probe the amplification dynamics of XRL in routine, and high electron density conditions to confirm gain-duration reduction resulting from ionization gating in the latter case. We also present recent results on the seeding of a vortex beam carrying orbital angular momentum (OAM) in XRL plasma. A small part of the high topological charge extreme ultraviolet (EUV) vortex is injected in XRL. These preliminary results suggest that the vortex seed indeed can be efficiently amplified. In the end, we propose a pathway towards the seeding of the complete vortex beam and wavefront characterization of the amplified beam.
We present an experimental intensity and wavefront characterization of the infrared vortex driver as well as the extreme ultraviolet vortex obtained through high harmonic generation in an extended generation medium. In a loose focusing geometry, an intense vortex beam obtained through phase-matched absorption-limited high harmonic generation in a 15 mm long Argon filled gas-cell permits single-shot characterization of the vortex structure. Moreover, our study validates the multiplicative law of momentum conservation even for such an extended generation medium.
The development in ultra-intense lasers aims at achieving the highest laser intensity on the target.
To ensure highest intensity, one has to accurately control spatial phase to get the smallest focused spot. The spatial phase is controlled using adaptive optics systems with a wavefront sensor to measure spatial phase and a deformable mirror to correct it. This adaptive optics system is commonly placed at the output of the laser chain (just before or just after the compressor) and it now becomes a standard feature on high-power laser chains. The usual strategy of adaptive optics correction is to separate a small fraction of the main beam and to measure its wavefront using a wavefront sensor. However such strategy only ensures that the laser beam is free from aberrations at the location of the wavefront sensor. Aberrations induced by the optical elements located downstream of the wavefront sensor, for instance focusing optics, are not measured and therefore are not corrected by the adaptive optics loop. These aberrations contribute to final focal spot degradation. In order to get the highest intensity on the target, an aberration-free wavefront in the interaction chamber after the focusing optics is required.
We will present a simple, direct and automated method using a standard focal spot camera and phase retrieval algorithms in order to measure and correct wavefront directly on the focal spot itself. This method is simple as it does not require additional hardware and can be used with spectral bandwidth larger than 200 nm.
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