Glass-based detector characterizes waveform of ultrafast few-cycle laser pulses
Garching, Germany--Characterizing the few-cycle femtosecond laser pulses used to produce extreme nonlinear optical phenomena for attosecond science is difficult; in particular, the relation of the pulses's carrier wave to the its envelope (the carrier-envelope phase, or CEP) is tough to measure. Now, researchers at the Laboratory for Attosecond Physics (LAP) at the Max-Planck-Institute of Quantum Optics, together with colleagues based at Ludwig-Maximilians-Universität München and the Technische Universität München (TUM), have created a detector that provides a detailed picture of the waveforms of few-cycle laser pulses.1
Unlike conventional gas-phase detectors, this one is made of glass, and measures the flow of electric current between two electrodes that is generated when the electromagnetic field associated with the laser pulse impinges on the glass. The researchers can then deduce the precise waveform of the pulse from the properties of the induced current. Knowledge of the exact waveform of the femtosecond pulse in turn makes it possible to reproducibly generate attosecond-scale (1 as = 10-18 s) light pulses for attosecond science.1
The few-cycle (1 to 2 complete cycles) pulses that can be produced by mode-locked lasers are preceded and followed by waves of lower amplitude that are rapidly attenuated. Knowing more about the precise form of the high-amplitude oscillations allows laser physicists to use them in an optimal manner to produce attosecond pulses.
The glass-based detector allows accurate determination of the form of the light waves that make up an individual femtosecond pulse. Over the past several years, physicists in the group have learned that when pulsed high-intensity laser light irradiates glass, it induces measurable amounts of electric current in the material (see Nature, 3 January 2013). Ferenc Krausz and his colleagues have now found that the direction of flow of the current generated by an incident femtosecond pulse depends on the exact form of its wave packet.
Glass versus high-vacuum setup
To calibrate the new glass detector, the researchers coupled their system with a conventional instrument, which measures the currents caused by the motions of liberated electrons in xenon gas. By comparing the currents induced in the new solid-state detector with the data obtained using the conventional apparatus, the team was able to characterize the performance of their new glass-based setup. The new instrument enormously simplifies measurements in the domain of ultrafast physical processes, because one can dispense with the use of cumbersome vacuum chambers.
REFERENCE: Tim Paasch-Colberg et al., Nature Photonics (2014); doi: 10.1038/nphoton.2013.348
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.