Breaking the 10 petawatt limit with new laser amplification

Ultra-intense and ultra-short lasers have a wide range of applications, encompassing basic physics, national security, industrial services and healthcare. In fundamental physics, these lasers have become a powerful tool for research on strong-field laser physics, especially for laser radiation sources, laser particle acceleration, vacuum quantum electrodynamics, etc.

A dramatic increase in maximum laser power, from the 1 petawatt “Nova” of 1996 to the 10 petawatt “Shanghai Ultra-Intense Ultrafast Laser Facility” (SULF) of 2017 and the “Extreme Light Infrastructure – Nuclear Physics ” of 10 petawatts of 2019 (ELI-NP), is due to a shift in the gain medium for large aperture lasers (from neodymium-doped glass to titanium: sapphire glass). This change reduced the pulse duration of high-energy lasers from about 500 femtoseconds (fs) to about 25 fs.

However, the upper limit for ultra-intense ultra-short titanium:sapphire lasers appears to be 10 petawatts. Currently, for 10-100 petawatt development planning, researchers generally abandon titanium/sapphire variable frequency pulse amplification technology and turn to parametric optical variable frequency pulse amplification technology, based on nonlinear crystals of deuterated potassium dihydrogen phosphate. This technology, due to its low pump-signal conversion efficiency and low spatio-temporal-spectral-energy stability, will pose a great challenge for the realization and application of future 10 to 100 petawatt lasers.

On the other hand, titanium/sapphire chirped pulse amplification technology, as a mature technology that has successfully realized two 10 petawatt lasers in China and Europe, still has great potential for the next stage development of ultra-short, ultra-intense lasers.

Titanium: Sapphire glass is a means of energy level type broadband laser gain. The pump pulse is absorbed to create a population inversion between the upper and lower energy levels, which completes the energy storage. When the signal pulse passes through the titanium/sapphire glass several times, the stored energy is extracted for laser signal amplification. However, in the case of a transverse parasitic laser, amplified spontaneous emission noise along the crystal diameter consumes the stored energy and reduces the amplification of the laser signal.

Currently, the maximum aperture of titanium/sapphire crystals can only support 10 petawatt lasers. Even with larger titanium/sapphire crystals, laser amplification is still not possible because strong transverse parasitic lasing increases exponentially as the size of the titanium/sapphire crystals increases.

In response to this challenge, researchers adopted an innovative approach that involves cohesively assembling multiple titanium and sapphire crystals. As shown in Advanced Photonics Nexusthis method exceeds the current 10 petawatt limit on ultra-intense ultra-short titanium:sapphire lasers, effectively increasing the aperture diameter of the entire tiled titanium:sapphire crystal and also truncating the transverse stray lasing effect in each crystal tile.

Corresponding author Yuxin Leng of the Shanghai Institute of Optics and Fine Mechanics notes: “Titanium and sapphire mosaic laser amplification was successfully demonstrated in our 100 terawatt laser system (i.e. i.e. 0.1 petawatt). We achieved almost ideal laser amplification using this system. technology, including high conversion efficiencies, stable energies, broadband spectra, short pulses and small focal points.

Leng’s team reports that coherent mosaic titanium:sapphire laser amplification provides a relatively simple and inexpensive way to exceed the current 10 petawatt limit.

“By adding a 2 × 2 coherent mosaic titanium sapphire high-energy laser amplifier into the Chinese SULF or European ELI-NP, the current 10 petawatts can be further increased to 40 petawatts and the maximum focused intensity can be increased by almost 10. times or more,” says Leng.

The method promises to improve the experimental capability of ultra-short, ultra-intense lasers for strong-field laser physics.