Current Status of High-Power Ultrashort Pulse Lasers And Laser Processing Systems: State-of-the-Art Developments

01 Introduction
Ultrashort pulse lasers, with pulse durations in the picosecond and femtosecond range, are becoming increasingly popular in precision laser micromachining. This article briefly outlines the current state of high-power ultrashort pulse lasers and laser processing systems, and summarizes the application fields of ultrashort pulse lasers.

02 kW-Class and GHz-Class Lasers
The average power of an ultrashort pulse laser is determined by the repetition rate and the single pulse energy, with average power being the product of pulse energy and repetition rate. High repetition rates and high pulse energies can result in extremely high laser powers. Currently, ultrashort pulse lasers used in research offer powers between 10W and 100W, which can be used to control irradiation on materials with a single laser spot. High-power lasers reaching 1kW are still under development. Thin-disk multi-pass amplifiers used for picosecond lasers can increase average output power to 1kW. Multi-pass, non-CPA ultrashort pulse Yb-doped thin-disk laser systems can deliver up to 1.9kW output power at a 400kHz repetition rate. At 25kHz in a four-pulse burst mode, the total energy can reach 46.7mJ. Using the Innoslab architecture, average powers up to 5kW and pulse energies in the joule range are achievable.
Besides high pulse energy, high repetition rate lasers offer new potential for material processing. Ultrahigh pulse repetition rates improve process efficiency. Lasers can reach GHz repetition rates and microjoule-level pulse energies in burst mode. Currently, industrial-grade 100W femtosecond GHz lasers have been developed, capable of delivering 1mJ total pulse energy at 100kHz, with adjustable number of pulses per burst. The intra-burst repetition rate can vary between 0.88 and 3.52 GHz.

03 Laser Processing Systems
Once the laser source is determined, the use of ultrashort pulse lasers in material processing also requires control by mechanical and optical systems to direct the position, orientation, and shape of the laser beam on the material.

3.1 Galvanometric and Polygon Scanners
The most convenient and rapid method of positioning a laser beam is via galvanometric scanners and polygon scanners. These work by tilting two mirrors without inertia in the vertical direction to quickly move the beam within a defined area. For example, a galvo scanner with an f-theta lens of 160mm focal length can move the beam at 20m/s within a 100mm×100mm area.
Polygon scanners, widely used in imaging, can move the beam at speeds up to 100m/s. Synchronised high-speed beam deflection using polygon scanners allows ultrashort pulse lasers to overcome plasma shielding and heat accumulation limits. With such high scanning speeds, pulse overlap is reduced, making high average power lasers highly effective for high-throughput material processing. Figure 1 shows the process of combining galvo and polygon scanners to deflect a laser beam in a 2D plane.
Studies have also shown that combining an acousto-optic deflector (AOD) with galvo scanners can extend dynamic performance over small ranges. AODs can deflect the beam pulse-by-pulse within their scanning field and modulate beam intensity simultaneously. Since AODs contain no mechanical components, they are also used to compensate for vibrations and overshoot from rapidly moving mirrors, reducing processing time and improving quality.

The rotating mirror is combined with a galvanometer scanner to achieve fast 2D laser beam deflection.

3.2 Beam Shaping
Most lasers emit beams with a Gaussian profile. This distribution, with high central intensity and low edges, often poses challenges in thin film processing. Beam shaping can optimize the beam profile for many laser material processing applications.
Diffractive optical elements (DOEs) can convert a Gaussian beam into a rectangular flat-top beam, concentrating intensity in the most useful part of the beam. However, this inevitably introduces some stray diffracted light, reducing shaping efficiency.
Free-form optics are increasingly used for beam shaping and can efficiently generate application-specific profiles. Spatial light modulators (SLMs), using computer-generated holograms, control the phase and amplitude of the beam. When combined with femtosecond lasers, SLMs can produce multiple diffracted beams for parallel processing, improving micromachining efficiency for silicon and titanium alloys by over tenfold.

04 Applications of Ultrafast Lasers in Micromachining
In ultrashort pulse laser processing, too little energy fails to produce permanent modifications such as ablation pits, while too much energy causes heating and plasma shielding, adversely affecting the workpiece. There exists an optimal irradiation condition for effective material removal.
The volume of laser ablation pits is influenced by the ablation threshold fluence of the material and the beam diameter at 1/e² intensity along with the corresponding central fluence. This model has been proven effective in various material processing applications.
Material removal rate is directly related to average laser power and can be increased by raising the pulse repetition rate. By adjusting focus offset and changing pulse energy, optimal ablation can be achieved.
Moreover, the parameter window for most efficient ablation also corresponds to the highest surface quality.

The influence of scanning speed and scanning line spacing on laser ablation performance: (a) The relationship between the surface roughness of the cavity bottom and the scanning speed and scanning spacing after a single scan. (b) The relationship between the ablation rate and the scanning speed and scanning spacing.

The figure below lists typical applications for different pulse energies and repetition rates. For example, perforating metal foils requires less than 10W average power, while glass cutting and interference patterning demand higher powers and pulse energies.

Typical ultrashort pulse laser applications based on pulse energy and repetition frequency.

05 Conclusion
Significant advancements have been made in the reliable generation, amplification, and shaping of ultrashort laser pulses in recent years. kW-class and GHz-class lasers enable high processing efficiency, while optimization of laser processing systems has broadened the application range of ultrashort pulse laser machining, greatly improving quality and throughput.
Under the guidance of theoretical frameworks, ultrashort pulse laser processing shows promising prospects and is expected to see broader industrial application in the future.

**--Cite the article published by 高能束加工技术 on April 23, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."