Laser Pulses with 1.2 Terawatt Peak Power

Impression of the compressor beamline to produce the short terawatt laser pulses. (Source: MBI)

In order to shed light on complex charge transfer mechanisms during the formation of a chemical bond or in biologi­cally relevant processes, one needs tools with exceptional temporal resolution in the attosecond realm. Single attosecond light pulses can be generated in the extreme ultra­violet (XUV) spectral range by focusing intense few-cycle laser pulses encom­passing only a few oscil­lations of the electric field onto noble gas atoms, using high-harmonic generation (HHG). However, the conversion effi­ciency is low, yielding very weak atto­second pulses, insuffi­cient for nonlinear spectro­scopic appli­cations. In order to create more intense isolated atto­second pulses, high-energy, near infrared, few-cycle driving laser pulses are required.

Now, researchers at the Max Born Institute MBI in Berlin have made a big step forward in the energy scaling of the driver pulses. The group succeeded to spectrally broaden and sub­sequently compress pulses of a titanium sapphire laser, which emits at a wavelength of 790 nm, to 3.8 fs duration (1.5 optical cycles) at an energy of 6.1 mJ, which is unpre­cedented at kilohertz repetition rate. Thus the peak power of the pulses exceeds the terawatt level. This result breaks a 10-year-old record achieved at RIKEN in Japan.

In order to achieve these results, a new 8.2 meter long compressor beamline was built around a 3.75 meter long, stretched flexible hollow-core fiber where spectral broade­ning took place as a result of nonlinear inter­action between the intense light pulses and helium atoms admitted into the capillary. The spectrally broadened pulses were then compressed by a set of chirped mirrors and charac­terized by an in-line dispersion scan device that was directly placed into the vacuum beamline that is constructed for subsequent high-harmonic gene­ration and XUV experiments. The new HCF compressor is an up-scaled version of a device that was recently developed in the frame­work of an inter­national colla­boration with partici­pation of the MBI. This new develop­ment paves the way towards table-top nonlinear attosecond XUV spectro­scopy.

Reference: T. Nagy et al.: Generation of above-terawatt 1.5-cycle visible pulses at 1 kHz by post-compression in a hollow fiber, Opt. Lett. 45, 3313 (2020); DOI: 10.1364/OL.395830

Link: Ultrafast Lasers and Nonlinear Optics, Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Berlin, Germany