Shenzhen Technology University | Advancing Kilowatt-Class Ultrafast Thin-Disk Laser Technology: A New Generation Industrial Laser Platform
Ultrafast lasers with high repetition rates (>500 kHz), large pulse energies (>1 mJ), high average powers (>1000 W), and high beam quality (M² < 1.5) are crucial for applications in advanced manufacturing, materials processing, EUV generation, attosecond light sources, and coherent X-ray generation. They have long been a goal for both research and industry.
Thin-disk lasers replace the traditional rod-shaped gain media with a disk-shaped thin-disk structure. This design overcomes the thermal lensing issues associated with high-power pumping in rod crystals and avoids the limitations of fiber structures in achieving high energy due to laser damage and nonlinear effects. It is currently considered one of the best solutions for achieving high pulse energy, high average power, ultrashort pulse durations, and extreme ultraviolet wavelengths, making it a prime candidate for next-generation industrial laser technology platforms.
Thin-disk multipass amplification is a leading technique for obtaining high energy, kilowatt-class, and high beam quality lasers. Using this approach, in 2020, a collaborative effort between Germany's TRUMPF and the University of Stuttgart resulted in the development of an ultrafast thin-disk laser with an average power exceeding 1.9 kW.
Recently, supported by the National Key Research and Development Program (2022YFB3605800), Professor Ruan Shuangchen and Associate Professor Liu Xing's team at Shenzhen Technology University employed a nearly collinear thin-disk multipass amplification technique. Through meticulous design of complex thin-disk multipass amplification cavities and thin-disk crystal thermal management, they addressed long-standing technical challenges in thin-disk multipass amplification. They achieved a high-performance laser output with a maximum average power of 1075 W at 800 kHz, a maximum single pulse energy of >1 mJ, pulse width of <7 ps, beam quality factor M² < 1.5, and extraction efficiency >57%.
The related results have been published in the journal *Laser & Photonics Reviews*. This research highlights the breakthroughs achieved by Professor Ruan Shuangchen and Associate Professor Liu Xing's team in the field of ultrafast thin-disk lasers, particularly in terms of high repetition rates, large pulse energies, high average powers, and excellent beam quality. These advancements are expected to drive the development of laser technology in advanced manufacturing, materials processing, and other applications.High Power Laser Science and Engineering(Sizhi Xu, Xing Liu, Yubo Gao, Zuoyuan Ou, Fayyaz Javed, Xingyu He, Haotian Lu, Junzhan Chen, Yewang Chen, Deqin Ouyang, Junqing Zhao, Xu Wu, Chunyu Guo, Cangtao Zhou, Qitao Lue,Shuangchen Ruan.Thin-disk multi-pass amplifier for kilowatt-class ultrafast lasers [J]. High Power Laser Science and Engineering, DOI: 10.1017/hpl.2024.XX)
The experimental setup is shown in Figure 1. The system consists of an ultrafast seed source and a multipass amplifier cavity. The seed source is a self-developed high-power ultrafast thin-disk laser that, at a repetition rate of 800 kHz, delivers an average power of 276 W, a pulse width of 6.8 ps, and a beam quality factor M² < 1.3. To ensure mode matching between the seed light injected into the multipass amplifier cavity and the pump light, the seed light is collimated to a spot diameter of 4.8 mm using a telescope system. The seed light is directed into the multipass amplifier cavity through a polarizer. The multipass cavity is composed of thin-disk crystals, a multi-stroke pump system, and an array of multipass amplifier plane mirrors.
The thin-disk laser head consists of a custom-made large-diameter Yb:YAG thin-disk crystal and a 48-stroke pump system. The crystal has a doping concentration of 9%, a diameter of 20 mm, and a thickness of 100 µm. The thin-disk crystal is manufactured using third-generation semiconductor technology, which achieves high-quality bonding between the Yb:YAG thin-disk crystal and the diamond heat sink. The pump source is a wavelength-locked zero-phonon-line LD at 969 nm, which reduces the quantum defect to 5.8%. All mirrors within the amplifier are plane mirrors, and the thin-disk crystals have a large radius of curvature (R > 40 m), allowing the beam to undergo nearly collinear propagation within the system for over 36 passes. This design minimizes nonlinear effects and prevents damage to optical components at high peak powers, ensuring thermal and mechanical stability of the amplifier cavity and thus achieving stable high-power laser output.
Figure 2 shows the output performance of the kilowatt-class ultrafast thin-disk laser system.
- Panel (a) presents the laser output power curve and the amplification extraction efficiency curve, with a maximum extraction efficiency of 57%.
- Panel (b) displays the pulse autocorrelation curve, showing a pulse width of 6.26 ps after amplification.
- Panel (c) illustrates the beam quality factor, with the multipass amplifier achieving a maximum output power of 1075 W at 800 kHz. At this maximum power, the beam quality factors are Mx² = 1.59 and My² = 1.43.
- Panel (d) demonstrates the power stability, with a normalized root mean square (RMS) < 1.67% at an output power of 1018 W.
