High-speed fixed-target serial virus crystallography.

We report a method for serial X-ray crystallography at X-ray free-electron lasers (XFELs), which allows for full use of the current 120-Hz repetition rate of the Linear Coherent Light Source (LCLS). Using a micropatterned silicon chip in combination with the high-speed Roadrunner goniometer for sample delivery, we were able to determine the crystal structures of the picornavirus bovine enterovirus 2 (BEV2) and the cytoplasmic polyhedrosis virus type 18 polyhedrin, with total data collection times of less than 14 and 10 min, respectively. Our method requires only micrograms of sample and should therefore broaden the applicability of serial femtosecond crystallography to challenging projects for which only limited sample amounts are available. By synchronizing the sample exchange to the XFEL repetition rate, our method allows for most efficient use of the limited beam time available at XFELs and should enable a substantial increase in sample throughput at these facilities.

Cerenkov-type second-harmonic spectroscopy in random nonlinear photonic structures.

We report on experimental and theoretical studies of Cerenkov-type second-harmonic generation in random nonlinear photonic structures with different two-dimensional distributions of the ferroelectric domains. We utilize Cerenkov-type second-harmonic generation spectroscopy to estimate the average ferroelectric domain size by analyzing the spatial Fourier spectrum of the domain patterns. This is measured by scanning the Cerenkov second-harmonic signal for different angles of incidence and light polarizations of the fundamental wave. By comparing the experimental results with numerically simulated Fourier spectra, the corresponding domain patterns are retrieved, which are in a good correspondence with images obtained by Cerenkov-type second-harmonic generation microscopy.

Domain-shape-based modulation of Cerenkov second-harmonic generation in multidomain strontium barium niobate.

We study experimentally and numerically the second-harmonic Cerenkov emission with two different characteristic azimuthal intensity distributions in strontium barium niobate with a random structure of χ2 nonlinearity. We monitor in situ the Cerenkov emission during domain switching and show that a change of domain size and shape results in a fourfold azimuthal modulation of the Cerenkov cone.

Room-temperature macromolecular crystallography using a micro-patterned silicon chip with minimal background scattering.

Recent success at X-ray free-electron lasers has led to serial crystallography experiments staging a comeback at synchrotron sources as well. With crystal lifetimes typically in the millisecond range and the latest-generation detector technologies with high framing rates up to 1 kHz, fast sample exchange has become the bottleneck for such experiments. A micro-patterned chip has been developed from single-crystalline silicon, which acts as a sample holder for up to several thousand microcrystals at a very low background level. The crystals can be easily loaded onto the chip and excess mother liquor can be efficiently removed. Dehydration of the crystals is prevented by keeping them in a stream of humidified air during data collection. Further sealing of the sample holder, for example with Kapton, is not required. Room-temperature data collection from insulin crystals loaded onto the chip proves the applicability of the chip for macromolecular crystallography. Subsequent structure refinements reveal no radiation-damage-induced structural changes for insulin crystals up to a dose of 565.6 kGy, even though the total diffraction power of the crystals has on average decreased to 19.1% of its initial value for the same dose. A decay of the diffracting power by half is observed for a dose of D1/2 = 147.5 ±â€…19.1 kGy, which is about 1/300 of the dose before crystals show a similar decay at cryogenic temperatures.

TakeTwo: an indexing algorithm suited to still images with known crystal parameters.

The indexing methods currently used for serial femtosecond crystallography were originally developed for experiments in which crystals are rotated in the X-ray beam, providing significant three-dimensional information. On the other hand, shots from both X-ray free-electron lasers and serial synchrotron crystallography experiments are still images, in which the few three-dimensional data available arise only from the curvature of the Ewald sphere. Traditional synchrotron crystallography methods are thus less well suited to still image data processing. Here, a new indexing method is presented with the aim of maximizing information use from a still image given the known unit-cell dimensions and space group. Efficacy for cubic, hexagonal and orthorhombic space groups is shown, and for those showing some evidence of diffraction the indexing rate ranged from 90% (hexagonal space group) to 151% (cubic space group). Here, the indexing rate refers to the number of lattices indexed per image.