Optics-on-a-chip for ultrafast manipulation of 350-MHz hard x-ray pulses.

Microelectromechanical systems (MEMS) are miniature devices integrated into a vast range of industrial and consumer applications. Optical MEMS are developed for dynamic spatiotemporal control in lightwave manipulation and communication as modulators, switches, multiplexers, spectrometer, etc. However, they have not been shown to function similarly in sub-nm wavelength regimes, namely, with hard x-rays, as high-brilliance pulsed x-rays have proven powerful for addressing challenges in time-domain science, from energy conversion to neurobiological control. While desirable temporal properties of x-ray pulses can be enhanced by optics, conventional x-ray optics are inherently massive in size, hence, never dynamic. We demonstrate highly ultrafast x-ray optics-on-a-chip based on MEMS capable of modulating hard x-ray pulses exceeding 350 MHz, 103× higher than any other mechanical modulator, with a pulse purity >106 without compromising the spectral brilliance. Moreover, the timing characteristics of the devices can be tuned on-the-fly to deliver optimal pulse properties to create a host of dynamic x-ray instruments and applications, impossible with traditional optics of 109× bulkier and more massive. The advent of the ultrafast optics-on-a-chip heralds a new paradigm of x-ray photonics, time-domain science, and accelerator diagnostics, especially at not only the future-generation light sources that offer coherent and high-frequency pulses but also lab-based facilities that normally do not offer timing structures.

Ultrafast photonic micro-systems to manipulate hard X-rays at 300 picoseconds.

Time-resolved and ultrafast hard X-ray imaging, scattering and spectroscopy are powerful tools for elucidating the temporal and spatial evolution of complexity in materials. However, their temporal resolution has been limited by the storage-ring timing patterns and X-ray pulse width at synchrotron sources. Here we demonstrate that dynamic X-ray optics based on micro-electro-mechanical-system resonators can manipulate hard X-ray pulses on time scales down to 300 ps, comparable to the X-ray pulse width from typical synchrotron sources. This is achieved by timing the resonators with the storage ring to diffract X-ray pulses through the narrow Bragg peak of the single-crystalline material. Angular velocities exceeding 107 degrees s-1 are reached while maintaining the maximum linear velocity well below the sonic speed and material breakdown limit. As the time scale of the devices shortens, the devices promise to spatially disperse the temporal width of X-rays, thus generating a temporal resolution below the pulse-width limit.

Getting to the core of the problem: origin of the luminescence from (Mg,Zn)O heterostructured nanowires.

We have measured the time-resolved, X-ray excited optical luminescence spectra from two types of MgxZn(1-x)O core-shell, heterostructured nanowires: type I, with a small x, wurtzite core, encased in a larger x, wurtzite sheath; and type II, with a wurtzite core (x approximately 0), encased in a rock-salt sheath (x>0.62). By monitoring the X-ray energy dependence of the various luminescence peaks, we have determined the local environment of the sites where these peaks originate.