Lasers have long enchanted the scientific and industrial communities with their ability to produce highly concentrated beams of light. While most people envision a continuous and powerful light beam when they hear the term “laser,” the evolving needs of science and industry have ushered in the development of lasers that emit short and powerful light pulses. These short pulses serve a multitude of applications, from precision machining of materials to the creation of high harmonic frequencies, including X-rays, which illuminate quick phenomena in the attosecond range—truly a billionth of a billionth of a second. A remarkable innovation in this field recently emerged from ETH Zurich, where a dedicated team led by Professor Ursula Keller set a new benchmark for pulsed laser performance.
Breaking Records with Short Pulses
The research team’s breakthrough was nothing short of monumental. By achieving an average power of 550 watts, they exceeded the previous record for laser pulse strength by more than 50%. This significant leap not only positions their laser as the strongest ever created via a laser oscillator but also enables it to produce extremely brief pulses lasting less than a picosecond, at an impressive rate of five million pulses per second. The peak power of these pulses reaches an astonishing 100 megawatts—sufficient energy to power 100,000 vacuum cleaners momentarily. Their findings, recently published in the journal Optica, underline the advancements made after years of persistent research.
At the heart of these powerful lasers lies the cutting-edge design of short pulsed disk lasers, a project that has been under continuous investigation by Keller’s research group for over two decades. The technology uses a thin 100-micrometer disk of crystal containing ytterbium atoms as the laser medium. Throughout their research journey, Keller and her team encountered numerous challenges, with many experiments leading to unexpected technical failures. Each setback, however, was an opportunity for insight, ultimately enhancing the reliability of short pulsed lasers in industrial use.
Two critical innovations led to their recent accomplishments. Firstly, the researchers employed a unique arrangement of mirrors that effectively prolongs the light passage through the disk repeatedly before emanating from the outcoupling mirror. This ingenious configuration amplifies the light dramatically while maintaining stability—an essential feature for high-performance lasers. Secondly, they revitalized the introduction of a specialized semiconductor mirror known as the Semiconductor Saturable Absorber Mirror (SESAM), first developed by Keller three decades ago. Unlike traditional mirrors that reflect light uniformly, SESAM’s reflective properties vary with the light intensity, allowing the laser to produce focused pulses instead of a steady beam.
The transition to pulsed output achieved through these innovations offers several advantages over conventional laser systems. In prior applications, achieving similar power levels necessitated sending weaker laser pulses through multiple amplifiers, a setup that generated excess noise and instability, complicating precision measurements—crucial in numerous scientific explorations. The new system, in contrast, directly amplifies high-power output from the oscillator, significantly reducing noise and improving measurement accuracy.
One of the most exciting prospects stemming from this achievement is the ability to shorten the laser pulses efficiently to only a few cycles. This capability enhances the feasibility of generating attosecond pulses, which have the potential to revolutionize time-resolved measurements in fundamental physics and chemistry.
Keller envisions a broad range of practical applications for these high-power, finely-tuned laser pulses. One promising avenue is the development of frequency combs that operate within the ultraviolet to X-ray spectrum, which hold the potential to facilitate the creation of far more precise timekeeping devices. Additionally, terahertz radiation generated from this innovative laser can serve as a powerful tool for material testing, opening doors for advancements in various scientific fields.
Ultimately, Keller’s team believes their continuous improvement of laser oscillators demonstrates their viability as formidable alternatives to conventional amplifier-based laser systems. This paradigm shift opens up new pathways for experimentation and measurement, foreshadowing a future replete with enhanced technological capabilities that could reshape our understanding of fundamental constants in physics.
The accomplishments from the ETH Zurich team not only set a remarkable new standard for pulsed laser technology but also represent a significant milestone in scientific innovation. The implications of this work extend far beyond the initial breakthroughs, signifying a transformative leap that could shape fields ranging from fundamental research to applied industrial sciences. With their relentless pursuit of excellence and innovative spirit, Keller’s team is paving the way for a new era of laser technology that holds tremendous promise for the future.