20. Jun. 2014
Article in Laser Focus World: "MIXSEL: Ultrafast goes simple"
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We explore and push the frontiers in ultrafast science and technology, using interdisciplinary understanding of the physics of lasers, semiconductors, and measurement technologies. Taking this competitive know-how, we understand and are able to control fundamental charge and energy transport with atomic spatial and attosecond temporal resolution.
Professor Keller invented and demonstrated a key new device - the semiconductor saturable absorber mirror (SESAM) - which demonstrated the first passively mode-locked diode-pumped solid-state laser in 1992 and solved a 25-year-old challenge. For almost two decades since then, the Keller group has continued to define and push the frontier in ultrafast solid-state lasers both with detailed theoretical models and with world-leading experimental results, demonstrating orders of magnitude improvement in key features such as pulse duration, energy, and repetition rate. Prof. Keller also helped to spearhead industrial transfer of this technology. Today most ultrashort lasers are based on SESAM modelocking, with important industrial applications ranging from optical communication, precision measurements, microscopy, ophthalmology, and micromachining. More recent work has expanded this approach to a new class of semiconductor lasers with wafer-scale integration of both the gain and the absorber into a vertical emitting structure, allowing the technology to potentially scale into high-volume markets.
Prof. Keller’s cutting edge laser technology enabled the world’s most accurate clocks – the optical clock and the attoclock. She made significant contributions to frequency comb generation and stabilization, which was also noted by the Nobel committee for Physics in 2005. In collaboration with Dr. Telle (PTB, Braunschweig), they pioneered self-referencing frequency comb stabilization from modelocked lasers. They introduced and made first feasibility demonstrations for several novel techniques to measure and stabilize the carrier envelope offset phase (i.e. CEO phase or CEP) fluctuations – which was published in 1999 well before the two first publications by Hall and Hänsch in 2000. For example Keller and Telle proposed the f-to-2f heterodyne technique which is being used today.
The stabilized frequency comb enabled her to invent the attoclock: a powerful, new, and unconventional tool to study fundamental processes in quantum mechanics – with attosecond accuracy using 1000 times longer laser pulses. She established the attoclock to measure the electron tunneling time for the first time in 2008 which is a highly debated topic in theoretical physics for the last 60 years. Attosecond pulses are generated with the attoline and attosecond transient absorption measurements reveal new insight in very fundamental processes such as the virtual dipole transition.
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