ELI-NP Thematics - Laser and Optic Science

Ultrashort structured light pulses: vortex pulses, post-compressed pulses, spatio-temporal couplings

High-intensity lasers, capable of achieving extreme energy concentrations, open the door to groundbreaking physics experiments that were once thought impossible. From table-top prototypes to monumental laser systems spanning the size of sports arenas, this relentless progress embodies humanity's quest for mastery over light. Control of the spatio-temporal distortions in the ultrashort pulses, the non-linear modulation of light, adaptive optics and revolutionary beam profiles like vortex-driven orbital angular momentum beams promise untapped potential, shaping a brighter, laser-powered future. The key to unleash the future is the simulation, measurement and control of these complex pulses.

Synchronization of the pulses at the femtosecond level

Simultaneous ultra-intense pulses open new paths for scientific investigations ranging from nuclear photonics to strong-field quantum electrodynamics. The temporal overlap to be achieved is of the order of the pulse duration, 23 fs. In experiments at HPLS of ELI-NP using two simultaneous pulses, it was shown that a temporal overlap of better than half the pulse duration (11 fs) can be maintained for over two-thirds of the shots, enabling high data rate experiments with simultaneous petawatt pulses. The ultimate goal in this respect would be to improve the synchronization of the pulses to provide, in a reproductible manner, a temporal superposition accuracy of about a tenth of the oscillation period of the light field ( 2.67fs/10), in order to perform coherent combination of the pulses, achieving 20 PW peak power and ultimate dual 10 PW pulse experiments control.

Optical components development and characterization

Optical components in ultrashort and ultraintense pulse laser systems face critical challenges due to the extreme conditions they encounter. The high peak intensities demand materials with exceptional damage thresholds to avoid degradation. Aberrations and wavefront distortions, caused by imperfections in the components, must be characterized and minimized to maintain a high-quality beam profile. Dispersion, which can stretch and weaken ultrashort pulses, poses a challenge, necessitating precision-engineered materials and coatings to preserve pulse integrity. Surface quality and specialized coatings are crucial to ensure smoothness, durability, and minimal optical losses. Additionally, nonlinear effects such as self-focusing and self-phase modulation can distort the beam under ultraintense conditions, complicating system performance. We develop and characterize optical components such as fast optical switches based on frustrated total internal reflection, helical phase plates and we investigate their laser induced damage threshold, material optical non-linearities and dispersion of coatings and materials.

Absorption and propagation of the laser pulses

Understanding propagation and absorption of ultrashort pulses paves the way for breakthroughs in medicine, energy, and material science. By mastering how ultrashort pulses propagate and are absorbed, we gain control over energy delivery in the target at unprecedented levels, opening the path towards reliable experiments with extreme light.

Water microjets with 15- to 70 µm diameters after ablation by a focused laser pulse in the air. The jets flowed downstream and the laser pulse propagated horizontally from right to left. The time delays written in the images represent the time elapsed from the laser pulse. The white or black arrows indicate the location of the leading shock waves. Panels (d1) and (d2) show shock waves transmitted inside the glass nozzles that produced the jet. The dimension bar 10 100 µm in all the images.