Ultra-intense ultrashort lasers have revolutionized various industries with their wide-ranging applications. From national security to healthcare, these lasers have proven to be an invaluable tool. They have significantly impacted basic physics research, contributing to the study of strong-field laser physics, laser-driven radiation sources, laser particle acceleration, vacuum quantum electrodynamics, and more. Over the years, there has been a notable increase in peak laser power, resulting in groundbreaking discoveries and advancements. In this article, we will explore the latest developments and challenges faced in the field of ultra-intense ultrashort lasers.
The journey of ultra-intense ultrashort lasers began with the 1-petawatt “Nova” laser in 1996. Since then, there have been remarkable advancements, such as the 10-petawatt “Shanghai Super-intense Ultrafast Laser Facility” (SULF) in 2017 and the 10-petawatt “Extreme Light Infrastructure—Nuclear Physics” (ELI-NP) in 2019. One of the key factors contributing to this increase in laser power is the shift in gain medium for large-aperture lasers. The transition from neodymium-doped glass to titanium:sapphire crystal has allowed for a significant reduction in pulse duration, from approximately 500 femtoseconds (fs) to about 25 fs.
While the advancements in titanium:sapphire ultra-intense ultrashort lasers have been remarkable, there appears to be an upper limit of 10-petawatt. Researchers are currently faced with the challenge of developing lasers with power ranging from 10-petawatt to 100-petawatt. To overcome this hurdle, they are exploring alternatives to titanium:sapphire chirped pulse amplification technology. Optical parametric chirped pulse amplification technology, based on deuterated potassium dihydrogen phosphate nonlinear crystals, shows promise. However, it presents its own set of challenges, including low pump-to-signal conversion efficiency and poor spatiotemporal-spectral-energy stability.
Despite the challenges associated with alternative technologies, researchers believe that the titanium:sapphire chirped pulse amplification technology still holds great potential for the development of ultra-intense ultrashort lasers. This mature technology has already successfully realized two 10-petawatt lasers in China and Europe. Titanium:sapphire crystal, as an energy-level-type broadband laser gain medium, allows for effective energy storage and amplification of laser signals. One of the limitations faced with large-aperture titanium:sapphire crystals is transverse parasitic lasing. Amplified spontaneous emission noise along the crystal diameter consumes stored energy and reduces signal laser amplification.
To overcome the challenges posed by transverse parasitic lasing, researchers have adopted an innovative approach. Through the coherent tiling of multiple titanium:sapphire crystals, they have successfully broken through the current 10-petawatt limit. This approach not only increases the aperture diameter of the entire tiled titanium:sapphire crystal but also truncates the transverse parasitic lasing within each tiling crystal. This breakthrough was reported in Advanced Photonics Nexus. The lead author, Yuxin Leng from the Shanghai Institute of Optics and Fine Mechanics, highlights the success of coherently tiled titanium:sapphire laser amplification in their 100-terawatt laser system. They achieved near-ideal laser amplification, including high conversion efficiencies, stable energies, broadband spectra, short pulses, and small focal spots.
The coherent tiling of titanium:sapphire crystals provides a cost-effective and feasible solution to surpass the current 10-petawatt limit. By introducing a 2×2 coherently tiled titanium:sapphire high-energy laser amplifier into existing facilities like SULF or ELI-NP, the laser power can be further increased to 40-petawatt, and the focused peak intensity can be enhanced by nearly 10 times or more. This method opens up new possibilities and significantly enhances the experimental capability of ultra-intense ultrashort lasers for strong-field laser physics research.
The advancement of ultra-intense ultrashort lasers has paved the way for groundbreaking discoveries in various fields. From basic physics research to industrial applications, the impact of these lasers is undeniable. While challenges in the development of higher-power lasers persist, the coherent tiling of titanium:sapphire crystals presents a promising solution. By harnessing the potential of this innovative approach, researchers can push the boundaries of laser power and enable scientific breakthroughs that were once thought impossible. The future of ultra-intense ultrashort lasers is bright, and it holds great promise for the advancement of technology and knowledge.