When we think of lasers, we often visualize a continuous, focused beam of light. This common perception reflects the capabilities of traditional lasers, which have widespread applications across various fields, including medicine, manufacturing, and telecommunications. However, the scientific community’s quest for innovation has led to a significant development: the need for short, powerful laser pulses. These brief bursts of light allow researchers to observe rapid processes in physics and chemistry, including phenomena taking place at the attosecond scale—one quintillionth of a second. A recent breakthrough from a team at ETH Zurich, led by Professor Ursula Keller, has established new benchmarks in laser technology, showcasing the potential of short pulsed lasers.
The ETH Zurich researchers have made strides that set a new record in the realm of laser pulses. With an impressive average power output of 550 watts, their laser surpasses earlier achievements by over 50%. This signifies the strongest pulse ever successfully generated from a laser oscillator. Remarkably, these pulses—and one must not overlook this detail—are not only the most powerful recorded but also extremely brief, lasting less than a picosecond. The laser operates at a rapid succession, emitting an astounding five million pulses per second. Such capabilities translate to peak powers estimated at 100 megawatts, enough to theoretically power 100,000 vacuum cleaners simultaneously.
The innovation behind this technological advancement lies in the meticulous engineering of short pulsed disk lasers, a focus of Keller’s research for over a quarter of a century. The thin disk of crystal, mere 100 micrometers thick and infused with ytterbium atoms, forms the core of the system. Throughout the years, Keller’s team faced various challenges that hindered further increases in power, often resulting in catastrophic failures of internal components. However, confronting these obstacles has provided invaluable insights, ultimately enhancing the reliability of short pulsed lasers and their industrial applications.
Moritz Seidel, a Ph.D. candidate in Keller’s lab, elaborates on the innovative mechanisms that allowed their record-setting performance. The researchers designed a unique arrangement of mirrors that ricocheted light multiple times within the laser medium before allowing it to exit. This setup enables significant amplification without sacrificing stability, a critical balance often challenging to strike in high-power laser systems.
Another groundbreaking aspect of this research is the use of a specialized mirror developed three decades ago—known as the Semiconductor Saturable Absorber Mirror (SESAM). Unlike standard mirrors, which reflect light uniformly, SESAM’s reflectivity is contingent upon the light’s intensity levels. This clever design plays an essential role in initiating concentrated light pulses instead of a steady beam.
For a laser to emit light effectively, the internal intensity must cross a predefined threshold. The SESAM mirror adeptly facilitates this transition by reflecting light energy already amplified several times, ensuring that when conditions are ripe, the system shifts into pulsed operation. Historically, systems capable of producing such high-intensity pulses relied on cumbersome external amplifiers, which often introduced noise and power fluctuations. By making these advancements directly within the laser oscillator, the ETH Zurich team has established a new paradigm with potential benefits for precision measurement applications.
The ramifications of these breakthroughs extend beyond increased laser efficiencies. Keller envisions exciting possibilities, including applications that encompass the development of frequency combs operating in the ultraviolet to X-ray range. Such innovations could revolutionize timekeeping, enabling the creation of ultra-precise clocks and offering the potential to challenge our understanding of natural constants.
Additionally, terahertz radiation—generated from this cutting-edge laser—could be harnessed for material testing in various settings, opening new avenues in research and quality control. Keller emphasizes that the significance of these pulse lasers extends to demonstrating that laser oscillators can serve as viable alternatives to traditional amplifier-based systems, enhancing the accuracy and dependability of measurements across scientific disciplines.
The advances made by Ursula Keller’s team at ETH Zurich mark a pivotal step forward in the realm of laser technology. With the ability to generate unprecedented short pulses at remarkable power levels, this research not only propels our scientific understanding forward but encourages innovation in practical applications. As these new laser systems continue to evolve, they promise to unlock further mysteries of the physical world, redefine measurement standards, and foster enhancements across multiple industries. In the continuing journey of laser science, we are just beginning to scratch the surface.