High-performance 4-nm-resolution X-ray tomography using burst ptychography.

Advances in science, medicine and engineering rely on breakthroughs in imaging, particularly for obtaining multiscale, three-dimensional information from functional systems such as integrated circuits or mammalian brains. Achieving this goal often requires combining electron- and photon-based approaches. Whereas electron microscopy provides nanometre resolution through serial, destructive imaging of surface layers, ptychographic X-ray computed tomography offers non-destructive imaging and has recently achieved resolutions down to seven nanometres for a small volume.

Graphene-silicon Schottky diodes.

We have fabricated graphene-silicon Schottky diodes by depositing mechanically exfoliated graphene on top of silicon substrates. The resulting current-voltage characteristics exhibit rectifying diode behavior with a barrier energy of 0.41 eV on n-type silicon and 0.

Quantum fluctuations in small lasers.

The dominant role of quantum fluctuations in determining the steady-state and transient response of a laser is demonstrated when there is a small number of particles in the system. In this regime, quantum fluctuations are found to suppress the lasing threshold and create a non-Poisson probability distribution for n discrete excited electronic states and s discrete photons. The correlation between n and s damps the averaged dynamic response of laser emission.

Electromagnetic response of broken-symmetry nanoscale clusters.

A microscopic, nonlocal response theory is developed to model the interaction of electromagnetic radiation with inhomogeneous nanoscale clusters. The breakdown of classical continuum-field Mie theory is demonstrated at a critical coarse-graining threshold, below which macroscopic plasmon resonances are replaced by molecular excitations with suppressed spectral intensity.

All-optical timing restoration using a hybrid time-domain chirp switch.

We demonstrate a hybrid time-domain chirp switch (TDCS) in which the nonlinear chirper is an AlGaAs waveguide and the soliton dispersive delay line is a polarization-maintaining fiber. The hybrid TDCS can restore timing in a switching or transmission system, and when combined with an optical amplifier, it can act as an ultrafast, all-optical regenerator for soliton pulses. The timing restoration concept is applicable to other non-linear materials with negligible walk-off, and the acceptable time window can be tailored by adjusting the width and intensity of a reference pulse.

Picosecond pump and probe spectroscopy utilizing freely propagating terahertz radiation.

We demonstrate the feasibility of scaling up a terahertz-pulse generation scheme for use with a 10-Hz amplified femtosecond laser system. Visible pulsed excitation combined with a far-infrared probe should prove to be a powerful picosecond time-resolved technique.