Ultra-intense ultrashort lasers wield a vast array of applications, spanning basic physics, national security, industrial services, and healthcare. In the realm of basic physics, these lasers stand as formidable tools for delving into strong-field laser physics, laser-driven radiation sources, laser particle acceleration, and vacuum quantum electrodynamics.
The trajectory of peak laser power has witnessed a remarkable surge, evolving from the 1996 1-petawatt “Nova” to the 2017 10-petawatt “Shanghai Super-intense Ultrafast Laser Facility” (SULF) and the 2019 10-petawatt “Extreme Light Infrastructure—Nuclear Physics” (ELI-NP). This surge can be attributed to the transition in the gain medium for large-aperture lasers, shifting from neodymium-doped glass to titanium:sapphire crystal. This shift has significantly reduced the pulse duration of high-energy lasers from approximately 500 femtoseconds (fs) to a mere 25 fs.
However, the upper threshold for titanium:sapphire ultra-intense ultrashort lasers appears capped at 10-petawatt. Current development plans for the 10-petawatt to 100-petawatt range often involve forsaking titanium:sapphire chirped pulse amplification technology in favor of optical parametric chirped pulse amplification technology. This shift, based on deuterated potassium dihydrogen phosphate nonlinear crystals, presents challenges due to its low pump-to-signal conversion efficiency and poor spatiotemporal-spectral-energy stability.
In contrast, the mature technology of titanium:sapphire chirped pulse amplification, which has successfully realized two 10-petawatt lasers in China and Europe, still holds substantial promise for the next-stage development of ultra-intense ultrashort lasers.
The titanium:sapphire crystal functions as an energy-level-type broadband laser gain medium. The pump pulse facilitates energy storage by building up a population inversion between the upper and lower energy levels. During the passage of the signal pulse through the titanium:sapphire crystal, the stored energy is extracted for laser signal amplification. However, challenges arise from transverse parasitic lasing, where amplified spontaneous emission noise along the crystal diameter diminishes stored energy and reduces signal laser amplification.
To overcome this hurdle, researchers have innovatively employed the coherent tiling of multiple titanium:sapphire crystals. As outlined in Advanced Photonics Nexus, this approach surpasses the current 10-petawatt limit on titanium:sapphire ultra-intense ultrashort lasers. It effectively increases the aperture diameter of the entire tiled titanium:sapphire crystal while curtailing transverse parasitic lasing within each tiled crystal.
Yuxin Leng, the corresponding author from the Shanghai Institute of Optics and Fine Mechanics, emphasizes, “The tiled titanium:sapphire laser amplification was successfully demonstrated in our 100-terawatt (0.1-petawatt) laser system. We achieved near-ideal laser amplification using this technology, including high conversion efficiencies, stable energies, broadband spectra, short pulses, and small focal spots.”
This innovative method offers a relatively straightforward and cost-effective means to surpass the current 10-petawatt limit. Leng envisions that incorporating a 2×2 coherently tiled titanium:sapphire high-energy laser amplifier into facilities like China's SULF or EU's ELI-NP could elevate the existing 10-petawatt capability to 40-petawatt, increasing the focused peak intensity by nearly tenfold or more.
This method holds the promise of enhancing the experimental capabilities of ultra-intense ultrashort lasers, particularly in the realm of strong-field laser physics.