The term “laser” typically evokes images of highly focused, continuous beams of light, a perception grounded in the traditional applications of laser technology. However, the landscape of laser research also encompasses a significant focus on generating brief, high-intensity bursts of light. Such short-pulsed laser technology enables remarkable advancements across various scientific and industrial domains. Researchers at ETH Zurich, led by the esteemed Professor Ursula Keller, have reached new heights in this segment by achieving unprecedented average power and pulse rates, marking a pivotal moment in laser technology history.
Recently, the team led by Keller attained a remarkable milestone: producing laser pulses at an average power of 550 watts, surpassing the previous record by over 50%. Notably, these pulses endure for less than a picosecond—equivalent to a millionth of a millionth of a second—demonstrating extraordinary speed. The laser emits approximately five million pulses per second, each exhibiting peak powers around 100 megawatts, enough to theoretically energize 100,000 vacuum cleaners momentarily. Such advancements are prominently documented in the journal Optica, underscoring the significance of this contribution to the field.
Keller’s team has been dedicated to the evolution of short-pulsed disk lasers for over 25 years, focusing on utilizing a thin crystal disk imbued with ytterbium atoms as the laser’s medium. Despite facing numerous technical challenges—some resulting in the destruction of various components—each setback contributed to a deeper understanding of laser mechanics, ultimately fostering advancements that enhance reliability and performance.
At the heart of this achievement lie two critical innovations. The first involves a sophisticated mirror arrangement that facilitates multiple internal reflections of light within the laser disk. This design amplifies the light effectively while ensuring stability, a common challenge typically encountered in high-power laser systems. According to Moritz Seidel, a Ph.D. student integral to the project, this strategy has proven invaluable in reaching the new power thresholds.
The second innovation centers on the Semiconductor Saturable Absorber Mirror (SESAM), conceived by Keller three decades ago. Differentiating itself from conventional mirrors, the SESAM’s reflectivity varies with the intensity of incoming light. This unique property allows the laser to naturally shift from emitting a continuous beam to generating short, high-intensity pulses. This transformation occurs because the SESAM reflects effectively under high light intensity, making it an essential component for achieving this cutting-edge functionality.
The recent advancements in short-pulsed laser technology open the door to numerous applications, particularly in the realm of precision measurement and frequency combs across a broad spectrum, including ultraviolet and X-ray regimes. Keller envisions these powerful, short pulses paving the way for enhanced measurement techniques, potentially leading to the creation of better atomic clocks. Such clocks may one day challenge the constancy of natural constants, presenting a fascinating avenue for exploration in fundamental physics.
Furthermore, this technology may facilitate the generation of terahertz radiation, which possesses significantly longer wavelengths than visible light. Terahertz radiation holds promise for material testing, offering a novel approach to non-destructive evaluation and characterization.
The groundbreaking work by Ursula Keller and her research team epitomizes a significant leap forward in laser technology. Their achievements in crafting powerful short-pulsed lasers position these systems as viable alternatives to traditional amplifier-based approaches. The implications of their work extend beyond merely harnessing enhanced power and speed; they herald a new era of precision and capability in measurements and applications across various scientific fields.
As this technology continues to evolve, researchers anticipate further innovations that will unlock even more possibilities, narrowing the gap between theoretical exploration and practical applications. The robust duality of power and pace achieved through short-pulsed lasers represents not only a scientific triumph but also a testament to persistent inquiry and ingenuity within the realm of quantum electronics.
Leave a Reply