The integration and development of ultrafast and ultra-intense laser and fiber laser coherent synthesis technology
summary
The high-intensity laser, characterized by ultra-short pulse and ultra-high peak power, provides unprecedented experimental means and extreme physical conditions for human beings, and has a wide range of application needs in major scientific and technological frontier fields such as advanced manufacturing, high-order harmonic generation, particle acceleration, and ultra-high-speed phenomenon research. However, due to the influence of thermo-optical effects and other factors, it is difficult to increase the average power and repetition rate of ultrafast and ultra-strong laser sources, and there is still a gap between them and related application requirements. In order to obtain ultrafast and ultra-intense lasers with higher average power, researchers generally believe that multi-channel fiber laser coherent synthesis is the preferred solution to achieve both high peak power and high average power ultrashort pulse lasers. From the perspective of the integration and development of ultrafast ultra-strong laser and fiber laser coherent synthesis technology, the research progress and development status at home and abroad in recent years are sorted out, and the development trend of high-power ultrafast ultra-strong laser based on coherent synthesis technology in China is prospected.
abstract
significance
High-intensity lasers have the characteristics of ultra-short pulses and ultra-high peak power, which provide unprecedented experimental possibilities and extreme physical conditions for mankind, so as to achieve various applications in major scientific and technological frontier fields such as advanced manufacturing, higher harmonic generation, particle acceleration, and ultra-high-speed phenomenon research. However, scaling the average power and repetition rate of ultrafast intensity lasers is challenging due to the limitations of the thermo-optical effect, and there is an order of magnitude difference between current technologies and related application requirements (Figure 1). To obtain an ultrafast intensity laser with a higher average power, the researchers employed a multi-channel fiber-laser-coherent beam combination (CBC) to simultaneously produce ultrashort laser pulses with high peak and average power levels. Specifically, fiber lasers can achieve high conversion efficiency (more than 30% electro-optical efficiency) through flexible and compact configurations due to the large surface-to-volume ratio and excellent thermo-optical properties due to the unique waveguide structure of the fiber, which is conducive to the realization of multi-channel CBC systems. However, demonstrating the CBC of ultrafast fiber lasers is challenging due to the need for high-precision control of multi-dimensional parameters such as delay, phase, beam direction, and polarization. Over the past 15 years, tremendous efforts have been made to address these issues, and significant progress has been made in scaling the average power and energy of ultrafast fiber laser CBC systems. Specifically, CBC has been further enhanced by the development of fiber laser time-domain CBC and multi-dimensional parameter control technology, reflecting the integrated development of ultrafast intensity laser technology and fiber laser CBC technology. Based on this viewpoint, this paper comprehensively reviews the research progress and development status of ultrafast fiber laser CBC at home and abroad in recent years, and looks forward to the development trend of domestic high-power ultrafast intensity lasers based on CBC technology.
progress
In the early stages of ultrafast fiber laser CBC, the general scheme was similar to that of CW lasers, i.e., spatial domain CBC, including tiled aperture and filler aperture configurations. The tiled aperture CBC was originally proposed for the International Coherent Amplification Network (ICAN) project (Figure 2), which aims to achieve a single pulse energy of 10 J and a repetition rate of 10 kHz by combining tens of thousands of fiber-chirped pulse amplifiers (CPAs). To date, the researchers have achieved a tiled aperture CBC for 61 channels (Figure 3), with a corresponding average power of only 25 W for a single channel. In addition, carding efficiency is inherently limited by the spatial duty cycle of the fiber laser array (up to 67%). At the same time, the filled-aperture CBC is based on a continuous combination of two collimated beams using spatial optics with a combined efficiency of 100% under ideal conditions (Figure 5). To date, ultrafast lasers with an average power of more than 10 kW have been achieved with 12 packed aperture CBCs of high-power CPAs (Figure 6), and power is expected to reach 100 kW.
For time-domain CBC, the main scheme is split-pulse amplification (DPA) and passive resonator-assisted pulse stacking. In principle, DPA utilizes polarization beam splitting and delay control to split a pulse into several discrete sub-pulses, which are then amplified (most likely in a single-channel CPA), and then combined into a single pulse by the opposite process of pulse splitting to achieve power and energy scaling (Figure 8). Pulse stacking includes two representative techniques, the stacking and pouring reinforcement chamber (Figure 10) and the Gires-Tournois interferometer (Figure 11), which stacks pulse trains into individual pulses to increase pulse energy at the cost of reducing repetition rate and average power. In recent years, in order to achieve high-power and high-energy ultrafast lasers, researchers have developed spatiotemporal CBC technology, which combines the advantages of spatiotemporal CBC. Currently, the technology has a maximum average power of 700 W and a pulse energy of 32 mJ. In addition, ultrafast lasers with an average power of several hundred kilowatts and pulse energies of tens of joules are considered compatible with this scheme .
Conclusions and prospects
The development of ultrafast fiber laser CBC technology in recent years has made it possible for fiber lasers to exhibit high power, high energy, and narrow pulse widths at the same time, enabling new applications. Nonetheless, the differences between relevant domestic and international research advances are significant. However, the ultrafast fiber laser CBC is expected to develop rapidly in China, and solid research results have been achieved in related cell technologies.