Non equilibrium studies on femtosecond timescales of quantum material systems are now offering a new avenues to further enhance understanding of equilibrium conditions, create new transient quantum phases, and disentangle energy/electron transport processes. In collaboration with QMI PIs S. Burke and A. Damascelli as well as MP-Stuttgart PI Kaiser we are continuing to develop new ultrafast lasers sources and related spectroscopy techniques to push these lines of study. Specific projects available for UTokyo students include:
Flexible VUV femtosecond lasers sources for time-resolved photoemission: Currently most all photon sources for time-resolved photoemission students have a fixed set of specific parameters (photon energy, repetition rate, polarization, spectral/temporal resolution, flux, etc.) that restrict each source to specific materials/physics studies. We are developing a new femtosecond VUV source based on based on phase-matching with soliton dispersion waves in gas-filled hollow core optical fibre which will expand opportunities for material studies
k-space optical tweezers: Through controlling the relative phase between a pair of optical pulses, it is possible to create (and control) asymmetric, excited-state electronic populations. While such effects have been measured macroscopically, a direct mapping of k-space using time-resolved angle-resolved photoemission has not been reported. By directly examining these artificial state preparations in k-space, we are pursuing transport and relaxation measurements that ultimately could offer applications toward spin-tronic and valley-tronic applications.
Spatio-temporal characterization of interfacial charge separation in organic photovoltaics:
We seek to improving the charge transfer (and hence efficiency) of organic photovoltaics (PV) by studying the coupled spatial-temporal dynamics of PV interfaces at the molecular level. Employing scanning probe microscopy (SPM) in tandem with time-resolved, angle-resolved photoemission spectroscopy (tr-ARPES) we seek to optimize PV’s conversion efficiencies by tracking (at the nanoscale) electronic and vibrational coupling in metal organic PV molecules and maximizing charge transfer at surface interfaces. Through these efforts we seek to record (simultaneously in both in the spatial and temporal domains) reaction pathways and associated quantum coherences through vibrational and electronic states following photoexcitation with goals of uncovering the mechanisms (and thus improving) energy transport in PVs.
Depending on choice of projects, students will get experience in
- femtosecond laser system design construction and optimization using both optical fibre and solid state components as well as a wide variety of laser diagnostic and characterization tools
- Molecular beam epitaxial growth of model organic photo-voltaic systems
- Scanning probe microscopy techniques.
- Photoemission spectroscopy measurement protocols and data analysis