Synchrotron beamlines typically use macroscopic, quasi-static optics to manipulate x-ray beams. We present the use of dynamic microelectromechanical systems-based optics (MEMS) to temporally modulate synchrotron x-ray beams. We demonstrate this concept using single-crystal torsional MEMS micromirrors oscillating at frequencies of 75 kHz. Such a MEMS micromirror, with lateral dimensions of a few hundred micrometers, can interact with x rays by operating in grazing-incidence reflection geometry; x rays are deflected only when an x-ray pulse is incident on the rotating micromirror under appropriate conditions, i.e., at an angle less than the critical angle for reflectivity. The time window for such deflections depends on the frequency and amplitude of the MEMS rotation. We demonstrate that reflection geometry can produce a time window of a few microseconds. We further demonstrate that MEMS optics can isolate x rays from a selected synchrotron bunch or group of bunches. With ray-trace simulations we explain the currently achievable time windows and suggest a path toward improvements.
Time-resolved synchrotron x-ray measurements often rely on using a mechanical chopper to isolate a set of x-ray pulses. We have started the development of micro electromechanical systems (MEMS)-based x-ray optics, as an alternate method to manipulate x-ray beams. In the application of x-ray pulse isolation, we recently achieved a pulse-picking time window of half a nanosecond, which is more than 100 times faster than mechanical choppers can achieve. The MEMS device consists of a comb-drive silicon micromirror, designed for efficiently diffracting an x-ray beam during oscillation. The MEMS devices were operated in Bragg geometry and their oscillation was synchronized to x-ray pulses, with a frequency matching subharmonics of the cycling frequency of x-ray pulses. The microscale structure of the silicon mirror in terms of the curvature and the quality of crystallinity ensures a narrow angular spread of the Bragg reflection. With the discussion of factors determining the diffractive time window, this report showed our approaches to narrow down the time window to half a nanosecond. The short diffractive time window will allow us to select single x-ray pulse out of a train of pulses from synchrotron radiation facilities.
We demonstrate the use of electrostatically driven micro-electromechanical systems (MEMS) devices to control and deliver synchrotron x-ray pulses at high repetition rates. Torsional MEMS micromirrors, rotating at duty cycles of 2 kHz and higher, were used to modulate grazing-incidence x rays, producing x-ray bunches shorter than 10 μs. We find that dynamic deformation of the oscillating micromirror is a limiting factor in the duration of the x-ray pulses produced, and we describe plans for reaching higher operating frequencies using mirrors designed for minimal deformation.
Over the past few decades, scientists have focused their attention on the development of concepts and designs, leading to demonstrations, of unique x-ray sources to perform femtosecond and attosecond science. The rewards of such an effort in the x-ray wavelength range will revolutionize the subfields of atomic physics, molecular physics, biology, condensed matter physics and material science. A brief review of this subject and its impact on emerging areas of science will be presented.
The storage-ring-based synchrotron radiation sources are today's workhorses in providing both time-averaged and time-resolved structural and chemical information with subnanosecond to subsecond resolution using x-ray imaging, spectroscopy and scattering techniques. On the other hand, many phenomena are ultrafast with characteristic periods of a few femtoseconds to tens of picoseconds. These include electronic motions around a nucleus in an atom, atomic and molecular vibrational motions in matter, spin dynamics, chemical and biological reactions, and phase transitions in response to photoexcitation. Probing such phenomena using photon-excited pump-probe experiments will require both optical and x-ray sources with comparable resolution. In the future, sources based on atypical concepts in storage-rings, table-top plasma sources, laser-based high harmonic generation (HHG) sources, linac-based sources, such as energy-recovery linacs (ERLs) and x-ray free-electron lasers (FELs), will likely meet these demands.