Sapphire laser amplification technology is expected to improve the experimental capabilities of ultra-powerful and ultra-short lasers in strong-field laser physics. Ultra-intense and ultra-short lasers have a wide range of applications, including fundamental physics, national security, industrial services and healthcare. In the field of basic physics, this type of laser has become a powerful tool for studying strong-field laser physics, especially in aspects such as laser-driven radiation sources, laser particle acceleration, and vacuum quantum electrodynamics.

Laser Power and Technology Development

From 1 Petawatt "Nova" in 1996 to 10 Petawatt "Shanghai Ultrafast Laser Facility" (SULF) in 2017 and 10 Petawatt "Aurora Infrastructure-Nuclear Physics" (ELI-NP) in 2019, the sharp increase in laser peak power is due to the transformation of the gain medium of large aperture lasers (from "Neodymium-doped glass" to "Titanium: sapphire crystal"). This shift shortens the pulse duration of high-energy lasers from around 500 femtoseconds (fs) to around 25 fs.

However, the upper limit of the titanium:sapphire ultra-powerful and ultra-short laser seems to be 10Petawatt. Currently, in the development plan of 10 to 100 Petawatt, researchers generally abandon titanium: sapphire chirped pulse amplification technology and instead adopt optical parametric chirped pulse amplification technology based on deuterated potassium dihydrogen phosphate nonlinear crystal.

This technology will pose a huge challenge to the implementation and application of 10-100Petawatt lasers in the future due to its low pump-to-signal conversion efficiency and poor spatiotemporal-spectral-energy stability. On the other hand, titanium: sapphire chirped pulse amplification technology is a mature technology, especially two 10Petawatt lasers have been successfully implemented in China and Europe, and it still has great potential in the next stage of the development of ultra-powerful and ultra-short lasers.

Titanium: Challenges for sapphire crystals

Titanium: sapphire crystal is an energy-level broadband laser gain medium. After the pump pulse is absorbed, a population inversion is formed between the upper energy level and the lower energy level, thereby completing energy storage. When the signal pulse passes through the titanium:sapphire crystal multiple times, the stored energy is extracted and used for laser signal amplification. However, in transverse parasitic lasers, the spontaneous emission noise along the crystal diameter direction is amplified, consuming the stored energy and reducing the amplification rate of the laser signal.

Currently, the maximum aperture of titanium:sapphire crystals can only support 10Petawatt lasers. Laser amplification is still not possible even with larger titanium:sapphire crystals because the intense lateral parasitic lasing increases exponentially as the size of the titanium:sapphire crystal increases.

Innovative solutions and future potential

To address this challenge, the researchers took an innovative approach by coherently tiling multiple titanium:sapphire crystals together. According to a report in the "Advanced Photonics Nexus" magazine on December 23, 2023, this method breaks through the current limit of 10 Petawatt of titanium: sapphire ultra-strong and ultra-short lasers, effectively increases the aperture of the entire tiled titanium: sapphire crystal, and also cuts off the lateral parasitic laser light within each tiled crystal.

Corresponding author Leng Yuxin from the Shanghai Institute of Optics and Fine Mechanics pointed out: "In our 100Terawatt (i.e. 0.1Petawatt) laser system, we successfully demonstrated tiled titanium: sapphire laser amplification. We used this technology to achieve near-ideal laser amplification effects, including high conversion efficiency, stable energy, broadband spectrum, short pulses and small focal spots."

The team reports that coherent tiled titanium:sapphire laser amplification technology provides a relatively simple and inexpensive way to surpass the current limit of 10 petawatts. "By adding a 2×2 coherent tiled titanium: sapphire high-energy laser amplifier to China's SULF or EU's ELI-NP, the current 10 petawatts can be further increased to 40 petawatts, and the focus peak intensity can be increased by nearly 10 times or even more." he said.

This method is expected to improve the experimental capabilities of ultra-intense and ultra-short lasers in strong-field laser physics.

Compiled source: ScitechDaily