K-M Group

Science and technology are inextricably linked and continue to drive each other. Ultrafast lasers have revolutionized our understanding of how molecules and materials work and how charges, spins, phonons and photons interact dynamically. In past research, our group designed Ti:sapphire lasers that operate at the limits of pulse duration and stability, with adjustable pulse durations from 7 fs on up. 

The demand for faster, more efficient, and more compact nanoelectronic devices, like smartphone chips, requires engineers to develop increasingly complex designs. To achieve this, engineers use layer upon layer of very thin films – as thin as only a couple strands of DNA – with impurities added, to tailor the function. 

Nanoparticles exhibit a surface-area-to-volume ratio many orders of magnitude higher than bulk materials, allowing them to serve as powerful catalysts for chemical reactions, both in the laboratory and as atmospheric aerosols.

Heat transport is driven by a thermal gradient, flowing from hot to cold regions in a material. However, at dimensions <100nm, bulk models no longer accurately predict the transport properties of materials. Because no complete models of nanoscale heat transport were available, it was assumed instead that bulk-like diffusive heat transport was valid—provided that an effective parameter, such as a size-dependent thermal conductivity, was incorporated.

Although x-ray imaging has been explored for decades, and visible-wavelength microscopy for centuries, it is only recently that the spectral region in between―the extreme ultraviolet (EUV)―has been explored for imaging nanostructures and nanomaterials.

High harmonics are ideal as the illumination source for time- and angle-resolved photoemission spectroscopy (trARPES), which can measure the full electronic band structure of a material. Moreover, a new generation of ultrafast (~50-100fs), MHz rep rate, VUV (1-20eV) highly-cascaded high harmonics driven by compact fiber lasers have 10-100meV energy resolution, and are ideal for spin-resolved ARPES (Optica 7, 832 (2020).

Magnetism has been the subject of scientific inquiry for more than 2000 years. However, it is still an incompletely understood phenomenon. The fundamental length and time scales for magnetic phenomena range from Å (exchange lengths) and sub-femtoseconds (exchange splitting) on up.