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  • Laser Design Brings Attosecond Spectroscopy Closer

Photonics.com
May 2015
MUNICH, May 7, 2015 — A new laser design could enable high-energy attosecond mid-wave IR and vacuum UV spectroscopy systems and faster optoelectronics.

The device is a diode-pumped Kerr-lens mode-locked Yb:YAG thin-disk laser combined with extracavity pulse compression. It was developed at the Laboratory for Attosecond Physics, which is run jointly by Ludwig Maximilian University of Munich and and the Max Planck Institute of Quantum Optics.

The Yb:YAG disk laser emits pulses lasting 7.7 fs, which corresponds to 2.2 wave periods. The average pulse power is 6 W, and each pulse carries 0.15 μJ of energy, 1.5 orders of magnitude greater than that attainable with commercial Ti:sapphire lasers.

Physicists already are able to control the waveform of the emitted pulses with considerable precision, but the new system extends this capacity even further.

Precise control of the temporal shape of the electromagnetic fields of the light waves is crucial for switching of electron flows in condensed matter and in single atoms, and hence for optoelectronics. Pulse lengths must be limited to a few femtoseconds.

The team's previous experiments showed it is possible to switch electric currents on and off using phase-controlled laser pulses. However, the maximum switching rates achieved in these experiments were on the order of a few thousands per second.

Their new laser is capable of producing tens of millions of high-power pulses per second. The approach is scalable to pulse energies of several microjoules and near-gigawatt peak powers, the researchers said, bringing generation of attosecond pulses at the full repetition rate of the oscillator into reach.

This field of ultrafast physics focuses on phenomena such as electron motions in molecules and atoms, which can take place on attosecond timescales. The ability to generate attosecond laser pulses would effectively permit electron motions to be "photographed."

Characterization of rare events at the microscale with the Ti:sapphire systems now used in attosecond laboratories requires observation times of hours or even days, assuming they can be captured at all. The new instrument improves data acquisition rates by a factor of 1000 to 100,000, making it possible to study such phenomena in far less time and in much greater detail.

Attosecond lasers could also be utilized to explore the elementary processes that underlie natural phenomena. Extreme UV pulses are sufficiently energetic to excite helium ions, which would allow the frequency of the associated emission to be precisely determined via the frequency-comb technique. This type of laser spectroscopy would provide a means of determining the values of constants of nature with extremely high precision, the researchers said.

Their research was published in Nature Communications (doi: 10.1038/ncomms7988).

For more information, visit www.en.uni-muenchen.de.


GLOSSARY
optoelectronics
A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.
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