Ultrafast electron localization and screening in a transition metal dichalcogenide.

The coupling of light to electrical charge carriers in semiconductors is the foundation of many technological applications. Attosecond transient absorption spectroscopy measures simultaneously how excited electrons and the vacancies they leave behind dynamically react to the applied optical fields. In compound semiconductors, these dynamics can be probed via any of their atomic constituents with core-level transitions into valence and conduction band.

Charge Carrier Inversion in a Doped Thin Film Organic Semiconductor Island.

Inducing an inversion layer in organic semiconductors is a highly nontrivial, but critical, achievement for producing organic field-effect transistor (OFET) devices, which rely on the generation of inversion, accumulation, and depletion regimes for successful operation. Here, we develop a pulsed bias technique to characterize the dopant type of any organic material system, without prior knowledge or characterization of the material in question. We use this technique on a pentacene/PTCDI heterostructure and thus deduce that pentacene is exhibiting -doped like response.

Nanoscale force sensing of an ultrafast nonlinear optical response.

The nonlinear optical response of a material is a sensitive probe of electronic and structural dynamics under strong light fields. The induced microscopic polarizations are usually detected via their far-field light emission, thus limiting spatial resolution. Several powerful near-field techniques circumvent this limitation by employing local nanoscale scatterers; however, their signal strength scales unfavorably as the probe volume decreases.

Phase stabilization of an attosecond beamline combining two IR colors.

We present a phase-stabilized attosecond pump-probe beamline involving two separate infrared wavelengths for high-harmonic generation (HHG) and pump or probe. The output of a Ti:sapphire laser is partly used to generate attosecond pulses via HHG and partly to pump an optical parametric amplifier (OPA) that converts the primary Ti:sapphire radiation to a longer wavelength. The attosecond pulse and down-converted infrared are recombined after a more than 20-m-long Mach-Zehnder interferometer that spans across two laboratories and separate optical tables.