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Sizing (ahar) has been used extensively in Turkish-Islamic handwritten documents. In this study, we present comparative experimental results including femtosecond (fs) and nanosecond (ns) pulsed laser cleaning of model paper samples with various types of sizing. The samples were artificially soiled with graphite and graphite-kaolinite mixture. For aging, the samples were exposed to air at 90 C temperature and 50% relative humidity during 16 days. Thickness variations of corn starch sizing were determined, and absorbance and transmittance values of corn, wheat and alum-egg sizing types at UV, VIS and IR wavelengths were measured for comparison. Two different methods and lasers were used for cleaning. In the first method, Yb:Glass fs laser beam (1030 nm wavelength) was focused on the paper surface by using a cylindrical lens (25 mm focal length). Square regions were cleaned through scanning the samples under laser light. Laser fluence was varied in the range of 0.39 - 0.78 J/cm(2). In the second method, a Q-switched Nd:YAG ns laser was operated at fundamental (1064 nm) and second harmonic (532 nm) wavelengths. Laser fluence was varied from 0.24 to 1.24 J/cm(2). Samples were cleaned by means of 1 and 10 laser shots for each fluence. The effectiveness of cleaning was investigated through measurements of color variations, visual and microscopic observations.

A femtosecond mode-locked soliton erbium-doped fiber laser (EDFL) is demonstrated using a commercially available nonconductive graphene oxide paper as a saturable absorber. The paper that is sandwiched between two fiber ferrules acts as a mode-locker. The EDFL generates a soliton mode-locked pulse train with a repetition rate of 15.62 MHz and pulsewidth of 680 fs. It is observed that the fiber laser has a low pulsing threshold as well as low damage threshold. The pulse energy and peak power are 0.0085 nJ and 11.85 W, respectively. The easy fabrication of graphene oxide paper should promote its potential application in ultrafast photonics.

Femtosecond laser ablation of freestanding reduced graphene oxide (rGO) paper and its mechanisms were investigated. An abnormal phenomenon was discovered: the ablated area remained unchanged for the rGO paper with an increasing number of pulses, which was found to be a general feature for a large range of laser fluences. We also studied femtosecond laser ablation of graphene oxide paper and highly oriented pyrolytic graphite film for comparison. Experimental results indicated that the abnormal phenomenon was unique to the rGO paper. As revealed by a combination of SEM, TEM, XRD and Raman techniques, femtosecond laser nonthermal ablation through rolling up of rGO nanoflakes, induced by the distinctive multi-level layer-by-layer structures and the ultrafast energy relaxation of the rGO paper, were considered to be responsible for the non-incubation effect.

Manufacturing fine metal mask (FMM) is the biggest hurdle to realize UHD grade AMOLED pixels for smartphone applications and even higher resolutions such as virtual reality displays. We have developed 800ppi or more grade fine metal mask processing system via femtosecond laser with unique thermal damage free process. Thanks to the unique processing strategy, without sacrificing the processing speed, UHD grade FMM is realized for AMOLED mobile displays.

Femtosecond (fs) cylindrical vector beams (CVBs) have found use in many applications in recent years. However, the existing rigid generation methods seriously limit its development. Here, we propose a flexible method for generating fs-CVBs with arbitrary polarization order by employing half wave plates and vortex retarders. The polarization state, autocorrelation width, pulse width, and spectrum features of the input and generated CVB pulses are measured and compared. The results verify that the generated CVBs remain in the fs regime with no appreciable temporal distortion, and the energy conversion efficiency can reach as high as 96.5%, even for a third-order beam. As a flexible way to generate fs-CVBs, this method will have great significance for many applications.

In this study, we demonstrate the precise control of fluid flow using femtosecond (FS) laser-induced microstructures. A microgroove structure inscribed on a poly(methyl methacrylate) (PMMA) substrate functions as a superhydrophilic membrane similar to paper. We first estimated the flow rate for pure water on microgrooves fabricated at various laser fluences in the range from 9.2 to 100.8 J/cm2. The results showed that the flow rate could be tuned in the range from 0.30 to 12.07 μL/s by varying the laser irradiation parameters. The fluid flow was reproducible, with a calculated relative standard deviation (RSD%) of less than 8% in the flow rate. We then fabricated a microfilter for blood separation and estimated its filtration ability using artificial blood containing resin microparticles. This method would be useful in a technology related to a paper-based diagnostic device for precise reagent manipulation.

Lasers have served as cleaning tools for historical objects and artworks for about 40 years. In many cases, superior results of laser cleaning were achieved with respect to traditional methods. In this technique, contaminations on the surface of the object are ablated by laser irradiation. In order to apply laser cleaning method to fragile materials such as paper made of cellulose or parchment, heat deposition to the bulk should be minimal, to prevent damage. In this work, it is demonstrated that laser pulses with femtosecond (fs) duration can exhibit non-thermal ablation of contaminants on paper samples. In particular, laser cleaning studies are concentrated on paper samples with sizing. Fs laser cleaning is performed on artificially soiled and aged samples, as well as on historical ones. The laser used in the experiments has pulse duration of 550 fs and 1030 nm center wavelength. The fluence of the laser is varied and the post-cleaning statuses of samples are investigated. The analyses are color changes, fiber integrity, chemical composition changes and mechanical strengths. These results show that fs lasers can be very efficient in cleaning paper samples, yielding minimal discoloration and no damage to fibers distinguishable on microscopic examination. The presence of sizing also provides further protection against possible side effects.

Cleaning of cultural assets, especially fragile organic materials like paper, is a part of the conservation process. Laser radiation as a non-contact tool offers prospects for that purpose. For the studies presented here, paper model samples were prepared using three different paper types (pure cellulose, rag paper, and wood-pulp paper). Pure cellulose serves as reference material. Rag and wood-pulp paper represent essential characteristics of the basic materials of real-world artworks. The papers were mechanically soiled employing pulverized charcoal. Pure and artificially soiled paper samples were treated with laser pulses of 28 fs (800 nm wavelength) and 8–12 ns (532 nm) duration in a multi pulse approach. Additionally, the cellulose reference material was processed with 30 ps (532 nm) laser pulses. Damage and cleaning thresholds of pure and soiled paper were determined for the different laser regimes. Laser working ranges allowing for removal of contamination and avoiding permanent modification to the substrate were found. The specimens prior and after laser illumination were characterized by light-optical microscopy (OM) and scanning electron microscopy (SEM) as well as multi spectral imaging analysis. The work extends previous nanosecond laser cleaning investigations on paper into the ultra-short pulse duration domain.

An overview of the major techniques to generate and detect THz radiation so far, especially the major approaches to generate and detect coherent ultra-short THz pulses using ultra-short pulsed laser, has been presented. And also, this paper, in particularly, focuses on broadband THz spectroscopy and addresses on a number of issues relevant to generation and detection of broadband pulsed THz radiation as well as broadband time-domain THz spectroscopy (THz-TDS) with the help of ultra-short pulsed laser. The time-domain waveforms of coherent ultra-short THz pulses from photoconductive antenna excited by femtosecond laser with different pulse durations and their corresponding Fourier-transformed spectra have been obtained via the numerical simulation of ultrafast dynamics between femtosecond laser pulse and photoconductive material. The origins of fringes modulated on the top of broadband amplitude spectrum, which is measured by electric-optic detector based on thin nonlinear crystal and extracted by fast Fourier transformation, have been analyzed and the major solutions to get rid of these fringes are discussed.

Wide range grade of pencils were used to draw on variety of sheet of papers. Raman spectroscopy and multimeter evaluate graphite structure and resistance of the area on the drawn paper before laser irradiation. The 10B grade of lead pencil draw on silver-halide print paper, and femtosecond laser was employed to irradiate the area of various papers drown by 10B lead pencil with varied scanning speed and laser power. At optimal conditions of laser irradiation, Raman spectroscopy verified the multi-graphene on the B10 pencil drawn silver-halide print paper irradiated by femtosecond laser.

Laser ablation offers cleaning method for historical and art works effectively. Difference between ablation threshold of contamination layer and the surface yields to remove contaminants from surface without detriment to historical material. In particular, lasers with ultrashort pulse duration are very convenient for brittle historical papers, fibers of which should be intact after cleaning treatment. Since duration of laser irradiation and material interaction is very short, the possibility of damage to the paper is very low. One of the other crucial issues after paper cleaning treatment is color variation on the surface. Authentic color of the historical paper has to be preserved after the procedure. In this paper, we present results of paper cleaning via femtosecond (fs) laser running at a wavelength of 1030 nm. In the first stage of this experimental study, we determined optimum laser parameters on artificially soiled and aged paper samples, then cleaned a handwritten manuscript with ‘sizing’. In calligraphy, ornamentation and miniature arts, sizing is applied on paper as a protective layer which increases strength of paper and renders it more useful. Papers with sizing have been prevalently used in Islamic or Ottoman culture. We observed that after laser irradiation, artificial soling layer is effectively removed, while original color of the subs-layers did not alter. We used scanning electron microscopy (SEM) to examine fiber integrity, and determined that the sizing layer was not removed when optimized parameters were used, thus the fibers were not damaged.

The terahertz paper photonic crystals, including one-dimensional stacks, two-dimensional square and hexagonal lattices as well as three-dimensional body-centered cubic lattice, are designed and fabricated. Femtosecond laser direct writing is employed to process paper layers. The transmission properties of these photonic crystals in THz range are characterized using time-domain THz spectroscopy. The experimental results are in good agreement with the numerical simulations and well explained by the photonic band-structure calculated by the plane wave expansion method. Our results demonstrate that paper photonic crystals have a good performance on molding the flow of THz radiation. From another point of view, the fabrication method proposed in this work can be widely extended to manufacture different micro-structures on various materials.

We use a broadband microbolometer array to measure the full three-dimensional (3D) terahertz (THz) intensity profile emitted from a two- color femtosecond plasma and subsequently focused in a geometry useful for nonlinear spectroscopic investigations. Away from the immediate focal region we observe a sharp, conical intensity profile resembling a donut, and in the focal region the beam collapses to a central, Lorentz-shaped profile. The Lorentzian intensity profile in the focal region can be explained by considering the frequency-dependent spot size derived from measurements of the Gouy phase shift in the focal region, and the transition from the donut profile to a central peak is consistent with propagation of a Bessel-Gauss beam, as shown by simulations based on a recent transient photocurrent model (You et al 2012 Phys. Rev. Lett. 109 183902). We combine our measurements to the first full 3D visualization of the conical THz emission from the two-color plasma.

Drawings were made on various types of paper using lead pencils of grades from 4H through 10B. Raman spectroscopy verified both G and D peaks on all the drawings on PC print paper, PC photopaper, kent paper, and paper for silver halide print. After irradiation with a scanning femtosecond laser, silver halide paper drawn on with a 10B lead pencil maintained its surface flatness compared with the other types of paper. Raman spectroscopy on silver print paper showed a high-intensity G peak and a low-intensity D peak. After irradiating the scanning femtosecond laser on silver halide paper drawn on with a 10B lead pencil, Raman spectroscopy showed a high-intensity G peak and less intense of D peak together with a 2D peak around 2,700 cm−1 corresponding to the existence of multigraphene.

Short-pulse lasers of femtosecond and picosecond durations are used in ultrahigh precision processing of optical, electronic, and micro-mechanical devices. In this paper we discuss the fabrication of high quality photonic crystal band-pass filters with femtosecond laser pulses. We also discuss the parallel processing of inkjet nozzles with a picosecond laser. A laser milling algorithm and a high accuracy beam scanner allows the formation of precisely shaped holes as inkjet nozzles, and an efficient diffractive beam splitter allows the simultaneous drilling of many hundreds of holes for low cost manufacturing.

A procedure of inspection of femtosecond laser induced mass transfer processes has been suggested that is based on pump-probe Doppler tomography. In the experiments we used mode-locked Ti:sapphire laser with output power up to 150 mW.. In our experiments focused laser radiation induced on the surface of the target mass transfer processes (melting and convection). The Doppler shifted backscattered radiation was registered by heterodyne scheme based on Michelson interferometer. We have obtained information about depth and distribution of convection flows within melted paraffin bath with high spatial resolution (Dz~15mm). We propose optical heterodyning technique based on OCT for obtaining temporal distribution of backscattered photons from media irradiated by Cr:forsterite femtosecond laser. The temporal resolution is about 60 fs. The technique was used for sheet paper porosity diagnostics.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have performed theoretical and experimental researches of spatio-temporal structure of femtosecond laser pulses, scattered in suspension of polysterol beads in water. The spatio-temporal structure of scattered pulses was measured by means of nonlinear optical gating at noncollinear second harmonic generation with subpicosecond temporal resolutions. Testing of phototoxic action of high-intensity femtosecond pulses on biological tissues has been performed with serum of rat's blood. Samples were irradiated with trains of 50-fs Ti:sapphire laser pulses with intensity up to a threshold of optical breakdown. The phototoxic stress of blood serum was defined with a several techniques including biochemoluminescence, sonoluminescence, and morphology analysis of dehydrated droplet, total concentration of proteins, viscosity and proteins oxidation measurements. We have determined regimes of blood serum irradiation with JR femtosecond laser pulses, corresponding to nonivasive influence, phototoxic stress and optical damage.

Advances in high power fibre lasers and amplifiers and in novel non-linear fibres that can be readily integrated with such pumps have led to a family of high power super-continuum sources that extend throughout the complete window of transparency of silica based fibres. The systems have been operated femtosecond, picosecond and nanosecond as well as cw. Average powers of 10’s Watts can be easily achieved, giving flat spectral power densities in excess of 10’s mW per nm from 400 nm to beyond 2.2 μm.

We report on the high power fiber based amplification of parabolic pulses. The output is compressed using transmission gratings to 300 fs and an average power of 38 W at 75 MHz repetition rate.

The Gd(0001) surface is investigated by femtosecond pump-probe experiments using laser pulses at 740-860 nm wave length. By non-linear optical second harmonic generation a coherent phonon-magnon mode at a frequency of 3 THz is observed which is excited through the exchange-split surface state. In parallel, electron-electron and electron-phonon interaction and their magnetic counterparts lead to incoherent dynamics of the electron, lattice, and spin subsystems. Variation of the optical wave length shows that for longer wave lengths up to 860 nm the coherent mode is excited predominantly while for shorter ones (less than or equal to 740 nm) incoherent contributions are favored. This presents a strong indication that depopulation of the occupied surface state component drives the coherent excitation. We find identical time scales for damping of the coherent mode and for electron-lattice equilibration which identifies electron-phonon scattering as an important relaxation channel for the coherent contribution. Increasing the temperature results in faster damping indicating that scattering of coherent phonons with thermal ones is an active relaxation channel as well.

The excitation-fluence and magnetic-field dependence of terahertz (THz) radiation power from InAs is investigated. For magnetic-field dependence, two completely different behaviors were observed depending on the excitation fluence. At low excitation fluence, the enhanced THz-radiation mainly originates from the carrier acceleration by the surface electric field. The Lorentz force changes the direction of carrier acceleration toward surface parallel, and the THz-radiation power is enhanced regardless of magnetic field direction. In contrast, at high excitation fluence, the surface electric field is almost screened out and the diffusion process becomes significant. By applying a magnetic field, the dipole is rotated to the direction in which the THz-radiation is efficiently or inefficiently extracted from the surface, and the radiation power is either enhanced or reduced depending on the magnetic-field direction. Additionally, from the magnetic-field dependence up to 27 T, it is found that THz-radiation power saturates at approximately 3 T and also at 13 T, and that the THz-radiation power at 3 T is much higher than that at 13 T. For the generation of broadband THz-radiation, focus is made on n-type InAs irradiated by ultrafast optical pulses. From the magnetic-field dependence of THz-radiation power, using n-type InAs under magnetic field is found to be the practical method to generate broadband THz-radiation, and the origin of higher-frequency component is identified to the hybrid modes.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We study the charge dynamics in a double quantum well and in ballistic mesoscopic rings driven by half-cycle pulses. It is shown that such pulses can be utilized to localize, within femtoseconds, and control, for picoseconds, the electronic motion in a Ga 1- x Al x As based double quantum well. To identify the pulse parameters that appropriate for an efficient control process we developed a simplified analytical model and corroborated the results by performing full numerical calculations. We also show that when a thin ballistic mesoscopic ring is subjected to a linearly polarized HCP a post-pulse (and therefore field-free) polarization is induced in the ring. The non-equilibrium post-pulse polarization oscillates in the ring as long as the coherence is preserved and decays on a time scale determined by the relaxation time.

Advances in laser micromachining have resulted in considerable processing capabilities for the growing MEMS/MOMS applications currently being developed. The two distinct temporal regimes for processing that are employed currently are ultrafast timescales at ~150fs and nanosecond timescales at >5 < 250ns. Reported results from various laser interaction studies reveal that the absence of heat affected zones cannot be guaranteed when using ultrafast interactions. This work presents experimental results from ablation studies of Ni in the ns and fs regimes. An important processing parameter, average scanned intensity, is defined along with experimentally derived values for ablation thresholds and the 2ω0 beam diameter for each of the optical setups. We apply electron back scattering diffraction (EBSD) analysis to target machined Ni surfaces from the fs and ns interactions to identify the creation or absence heat affected zones. Results from the study of EBSD data suggest that low intensity ultrafast interactions are capable of eliminating heat affected zones on condition that surface plasmas are not sustained above the interaction site. There is clear evidence of substantial heat affected zones when using nanosecond pulses at a wavelength of 355nm.

In order to investigate the ultrafast dynamics of free carriers generated in bulk dielectrics by intense femtosecond laser pulses we have designed a setup for ultrafast time-resolved imaging Mach-Zehnder interferometry. The application of the 2D-Fourier-transform technique allows us to accurately reconstruct the actual laser-induced phase shifts and transmission changes for the probe pulses, which provide the properties of free carriers. Interferometric measurements in high-purity fused silica clearly demonstrate that the dominant ionization mechanism for intensities below 10 TW/cm 2 is multiphoton ionization.

A long plasma channel, formed due to the dynamic balance between the nonlinear self-focusing and the plasma defocusing in the propagation of intense femtosecond laser pulses in air, is demonstrated to be able to continuously propel a paper airplane without complicated focusing optics. The maximum coupling coefficient generated by the plasma channel is found to be more than 8.5 dyne/W. In the plasma channel, the detonation wave generation with the air ionization is found to be the propulsive source.

Femtosecond white-light continuum probe transient absorption and reflectivity measurements of bulk graphite and graphene paper are reported. In graphite, the relaxation of photoinduced electron–hole pairs happens through in-plane electron–electron and electron–phonon scattering in similar, equals200 fs, while the ps dynamics is due to the modulation of the electronic structure by out-of-plane structural motions. The ps dynamics of the optical signal is strongly reduced in graphene paper, where the out-of-plane bond is disrupted, while the short component of the dynamics is identical in both materials. These results show that in 2D-graphene, the carrier relaxation occurs in similar, equals200 fs.

IUCrJ 8(6), 905 - 920 (2021). doi:10.1107/S2052252521008046, Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables essentially radiation-damage-free macromolecular structure determination using microcrystals that are too small for synchrotron studies. However, SFX experiments often require large amounts of sample in order to collect highly redundant data where some of the many stochastic errors can be averaged out to determine accurate structure-factor amplitudes. In this work, the capability of the Swiss X-ray free-electron laser (SwissFEL) was used to generate large-bandwidth X-ray pulses [$����/��$ = 2.2% full width at half-maximum (FWHM)], which were applied in SFX with the aim of improving the partiality of Bragg spots and thus decreasing sample consumption while maintaining the data quality. Sensitive data-quality indicators such as anomalous signal from native thaumatin micro-crystals and de novo phasing results were used to quantify the benefits of using pink X-ray pulses to obtain accurate structure-factor amplitudes. Compared with data measured using the same setup but using X-ray pulses with typical quasi-monochromatic XFEL bandwidth (����/�� = 0.17% FWHM), up to fourfold reduction in the number of indexed diffraction patterns required to obtain similar data quality was achieved. This novel approach, pink-beam SFX, facilitates the yet underutilized de novo structure determination of challenging proteins at XFELs, thereby opening the door to more scientific breakthroughs., Published by Chester

IUCrJ 8(4), 665 - 677 (2021). doi:10.1107/S2052252521005297, The crystallization of recombinant proteins in living cells is an exciting new approach in structural biology. Recent success has highlighted the need for fast and efficient diffraction data collection, optimally directly exposing intact crystal-containing cells to the X-ray beam, thus protecting the in cellulo crystals from environmental challenges. Serial femtosecond crystallography (SFX) at free-electron lasers (XFELs) allows the collection of detectable diffraction even from tiny protein crystals, but requires very fast sample exchange to utilize each XFEL pulse. Here, an efficient approach is presented for high-resolution structure elucidation using serial femtosecond in cellulo diffraction of micometre-sized crystals of the protein HEX-1 from the fungus Neurospora crassa on a fixed target. Employing the fast and highly accurate Roadrunner II translation-stage system allowed efficient raster scanning of the pores of micro-patterned, single-crystalline silicon chips loaded with living, crystal-containing insect cells. Compared with liquid-jet and LCP injection systems, the increased hit rates of up to 30% and reduced background scattering enabled elucidation of the HEX-1 structure. Using diffraction data from only a single chip collected within 12 min at the Linac Coherent Light Source, a 1.8 Å resolution structure was obtained with significantly reduced sample consumption compared with previous SFX experiments using liquid-jet injection. This HEX-1 structure is almost superimposable with that previously determined using synchrotron radiation from single HEX-1 crystals grown by sitting-drop vapour diffusion, validating the approach. This study demonstrates that fixed-target SFX using micro-patterned silicon chips is ideally suited for efficient in cellulo diffraction data collection using living, crystal-containing cells, and offers huge potential for the straightforward structure elucidation of proteins that form intracellular crystals at both XFELs and synchrotron sources., Published by Chester

A method for determining the sample flow rate and concomitant light condition in time-resolved serial femtosecond crystallography is developed to analyze the intermediate-state structures of photosystem II., Photosystem II (PSII) catalyzes light-induced water oxidation through an Si-state cycle, leading to the generation of di-oxygen, protons and electrons. Pump–probe time-resolved serial femtosecond crystallography (TR-SFX) has been used to capture structural dynamics of light-sensitive proteins. In this approach, it is crucial to avoid light contamination in the samples when analyzing a particular reaction intermediate. Here, a method for determining a condition that avoids light contamination of the PSII microcrystals while minimizing sample consumption in TR-SFX is described. By swapping the pump and probe pulses with a very short delay between them, the structural changes that occur during the S1-to-S2 transition were examined and a boundary of the excitation region was accurately determined. With the sample flow rate and concomitant illumination conditions determined, the S2-state structure of PSII could be analyzed at room temperature, revealing the structural changes that occur during the S1-to-S2 transition at ambient temperature. Though the structure of the manganese cluster was similar to previous studies, the behaviors of the water molecules in the two channels (O1 and O4 channels) were found to be different. By comparing with the previous studies performed at low temperature or with a different delay time, the possible channels for water inlet and structural changes important for the water-splitting reaction were revealed.

The facile fabrication of free-floating organic nanocrystals (ONCs) was achieved via the kinetically controlled self-assembly of simple perylene diimide building blocks in aqueous medium. The ONCs have a thin rectangular shape, with an aspect ratio that is controlled by the content of the organic cosolvent (THF). The nanocrystals were characterized in solution by cryogenic transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering. The ONCs retain their structure upon drying, as was evidenced by TEM and atom force microscopy. Photophysical studies, including femtosecond transient absorption spectroscopy, revealed a distinct influence of the ONC morphology on their photonic properties (excitation energy transfer was observed only in the high-aspect ONCs). Convenient control over the structure and function of organic nanocrystals can enhance their utility in new and developed technologies.

A 1.5 Å resolution crystal structure of bovine trypsin at room temperature has been determined using 150 fs X-ray diffraction snapshots at the FemtoMAX beamline of the MAX IV facility., Protein dynamics contribute to protein function on different time scales. Ultrafast X-ray diffraction snapshots can visualize the location and amplitude of atom displacements after perturbation. Since amplitudes of ultrafast motions are small, high-quality X-ray diffraction data is necessary for detection. Diffraction from bovine trypsin crystals using single femtosecond X-ray pulses was recorded at FemtoMAX, which is a versatile beamline of the MAX IV synchrotron. The time-over-threshold detection made it possible that single photons are distinguishable even under short-pulse low-repetition-rate conditions. The diffraction data quality from FemtoMAX beamline enables atomic resolution investigation of protein structures. This evaluation is based on the shape of the Wilson plot, cumulative intensity distribution compared with theoretical distribution, I/σ, R merge/R meas and CC1/2 statistics versus resolution. The FemtoMAX beamline provides an interesting alternative to X-ray free-electron lasers when studying reversible processes in protein crystals.

A pixel-based approach for extracting structure factors from X-ray free-electron laser crystal diffraction measurements is presented., Most crystallographic data processing methods use pixel integration. In serial femtosecond crystallography (SFX), the intricate interaction between the reciprocal lattice point and the Ewald sphere is integrated out by averaging symmetrically equivalent observations recorded across a large number (104−106) of exposures. Although sufficient for generating biological insights, this approach converges slowly, and using it to accurately measure anomalous differences has proved difficult. This report presents a novel approach for increasing the accuracy of structure factors obtained from SFX data. A physical model describing all observed pixels is defined to a degree of complexity such that it can decouple the various contributions to the pixel intensities. Model dependencies include lattice orientation, unit-cell dimensions, mosaic structure, incident photon spectra and structure factor amplitudes. Maximum likelihood estimation is used to optimize all model parameters. The application of prior knowledge that structure factor amplitudes are positive quantities is included in the form of a reparameterization. The method is tested using a synthesized SFX dataset of ytterbium(III) lysozyme, where each X-ray laser pulse energy is centered at 9034 eV. This energy is 100 eV above the Yb3+ L-III absorption edge, so the anomalous difference signal is stable at 10 electrons despite the inherent energy jitter of each femtosecond X-ray laser pulse. This work demonstrates that this approach allows the determination of anomalous structure factors with very high accuracy while requiring an order-of-magnitude fewer shots than conventional integration-based methods would require to achieve similar results.

A new one-dimensional fixed-target sample delivery method combined with a real-time visual servo scan system has been developed for serial femtosecond crystallography. The developed high-throughput microcrystal delivery system shows significant improvements for microcrystal delivery efficiency at an optimal crystal stability and significantly reduced sample consumption to reveal protein structures utilizing X-ray free-electron laser pulses., Microcrystal delivery methods are pivotal in the use of serial femtosecond crystallography (SFX) to resolve the macromolecular structures of proteins. Here, the development of a novel technique and instruments for efficiently delivering microcrystals for SFX are presented. The new method, which relies on a one-dimensional fixed-target system that includes a microcrystal container, consumes an extremely low amount of sample compared with conventional two-dimensional fixed-target techniques at ambient temperature. This novel system can deliver soluble microcrystals without highly viscous carrier media and, moreover, can be used as a microcrystal growth device for SFX. Diffraction data collection utilizing this advanced technique along with a real-time visual servo scan system has been successfully demonstrated for the structure determination of proteinase K microcrystals at 1.85 Å resolution.

The interaction of picosecond laser pulses with solid surfaces is characterized by ultra-fast energy transfer from the electronic system to the lattice. The present understanding of the elementary mechanisms responsible for carrier thermalization and cooling is briefly reviewed. In semiconductors, the electron hole plasma acts as intermediate energy storage. Recombination limits the maximum density and determines lattice heating in degenerate conditions. Experiments with femtosecond and picosecond laser sources have unraveled the salient features of the energy dissipation routes from photons to lattice.

Significance: Recent advances in nonlinear optics in neuroscience have focused on using two ultrafast lasers for activity imaging and optogenetic stimulation. Broadband femtosecond light sources can obviate the need for multiple lasers by spectral separation for chromatically targeted excitation. Aim: We present a photonic crystal fiber (PCF)-based supercontinuum source for spectrally resolved two-photon (2P) imaging and excitation of GCaMP6s and C1V1-mCherry, respectively. Approach: A PCF is pumped using a 20-MHz repetition rate femtosecond laser to generate a supercontinuum of light, which is spectrally separated, compressed, and recombined to image GCaMP6s (930 nm excitation) and stimulate the optogenetic protein, C1V1-mCherry (1060 nm excitation). Galvanometric spiral scanning is employed on a single-cell level for multiphoton excitation and high-speed resonant scanning is employed for imaging of calcium activity. Results: Continuous wave lasers were used to verify functionality of optogenetic activation followed by directed 2P excitation. Results from these experiments demonstrate the utility of a supercontinuum light source for simultaneous, single-cell excitation and calcium imaging. Conclusions: A PCF-based supercontinuum light source was employed for simultaneous imaging and excitation of calcium dynamics in brain tissue. Pumped PCFs can serve as powerful light sources for imaging and activation of neural activity, and overcome the limited spectra and space associated with multilaser approaches.

New organic THz generators are designed herein by molecular engineering of the refractive index, phonon mode, and spatial asymmetry. These benzothiazolium crystals simultaneously satisfy the crucial requirements for efficient THz wave generation, including having nonlinear optical chromophores with parallel alignment that provide large optical nonlinearity; good phase matching for enhancing the THz generation efficiency in the near‐infrared region; strong intermolecular interactions that provide restraining THz self‐absorption; high solubility that promotes good crystal growth ability; and a plate‐like crystal morphology with excellent optical quality. Consequently, the as‐grown benzothiazolium crystals exhibit excellent characteristics for THz wave generation, particularly at near‐infrared pump wavelengths around 1100 nm, which is very promising given the availability of femtosecond laser sources at this wavelength, where current conventional THz generators deliver relatively low optical‐to‐THz conversion efficiencies. Compared to a 1.0‐mm‐thick ZnTe crystal as an inorganic benchmark, the 0.28‐mm‐thick benzothiazolium crystal yields a 19 times higher peak‐to‐peak THz electric field with a broader spectral bandwidth (>6.5 THz) when pumped at 1140 nm. The present work provides a valuable approach toward realizing organic crystals that can be pumped by near‐infrared sources for efficient THz wave generation., Organic crystals, which are designed through molecular engineering of the refractive index, phonon mode, and spatial asymmetry, simultaneously satisfy the crucial requirements for efficient and broadband THz wave generation, particularly at near‐infrared pump wavelengths near 1100 nm.

The ability to rapidly obtain structures of protein–ligand complexes using X-ray crystallography is central to drug discovery, but the typical cryocooling of samples and the effects of the X-ray beam may distort the observed ligand binding. X-ray free-electron lasers (XFELs) have the promise to solve these issues, but methods to rapidly produce structures of protein–ligand complexes at XFELs have not yet been realized. Here, an efficient solution using high-throughput, fixed-target serial femtosecond crystallography at an XFEL is demonstrated., High-throughput X-ray crystal structures of protein–ligand complexes are critical to pharmaceutical drug development. However, cryocooling of crystals and X-ray radiation damage may distort the observed ligand binding. Serial femtosecond crystallography (SFX) using X-ray free-electron lasers (XFELs) can produce radiation-damage-free room-temperature structures. Ligand-binding studies using SFX have received only modest attention, partly owing to limited beamtime availability and the large quantity of sample that is required per structure determination. Here, a high-throughput approach to determine room-temperature damage-free structures with excellent sample and time efficiency is demonstrated, allowing complexes to be characterized rapidly and without prohibitive sample requirements. This yields high-quality difference density maps allowing unambiguous ligand placement. Crucially, it is demonstrated that ligands similar in size or smaller than those used in fragment-based drug design may be clearly identified in data sets obtained from

A high-viscosity cartridge-type injector for serial femtosecond crystallography has been developed at SPring-8 Angstrom Compact Free-Electron Laser., A sample-injection device has been developed at SPring-8 Angstrom Compact Free-Electron Laser (SACLA) for serial femtosecond crystallography (SFX) at atmospheric pressure. Microcrystals embedded in a highly viscous carrier are stably delivered from a capillary nozzle with the aid of a coaxial gas flow and a suction device. The cartridge-type sample reservoir is easily replaceable and facilitates sample reloading or exchange. The reservoir is positioned in a cooling jacket with a temperature-regulated water flow, which is useful to prevent drastic changes in the sample temperature during data collection. This work demonstrates that the injector successfully worked in SFX of the human A2A adenosine receptor complexed with an antagonist, ZM241385, in lipidic cubic phase and for hen egg-white lysozyme microcrystals in a grease carrier. The injection device has also been applied to many kinds of proteins, not only for static structural analyses but also for dynamics studies using pump–probe techniques.

A method is described that enables both time- and sample-efficient X-ray crystallographic data collection from radiation-sensitive protein microcrystals and direct comparison of the resulting dose-resolved serial synchrotron and damage-free X-ray free-electron laser structures. It is demonstrated that real-space extrapolation from a synchrotron dose series reproduces key features of the damage-free structure obtained using an X-ray free-electron laser., An approach is demonstrated to obtain, in a sample- and time-efficient manner, multiple dose-resolved crystal structures from room-temperature protein microcrystals using identical fixed-target supports at both synchrotrons and X-ray free-electron lasers (XFELs). This approach allows direct comparison of dose-resolved serial synchrotron and damage-free XFEL serial femtosecond crystallography structures of radiation-sensitive proteins. Specifically, serial synchrotron structures of a heme peroxidase enzyme reveal that X-ray induced changes occur at far lower doses than those at which diffraction quality is compromised (the Garman limit), consistent with previous studies on the reduction of heme proteins by low X-ray doses. In these structures, a functionally relevant bond length is shown to vary rapidly as a function of absorbed dose, with all room-temperature synchrotron structures exhibiting linear deformation of the active site compared with the XFEL structure. It is demonstrated that extrapolation of dose-dependent synchrotron structures to zero dose can closely approximate the damage-free XFEL structure. This approach is widely applicable to any protein where the crystal structure is altered by the synchrotron X-ray beam and provides a solution to the urgent requirement to determine intact structures of such proteins in a high-throughput and accessible manner.

A two-bunch scheme to generate high-power, high-repetition-rate THz radiation for pump–probe experiments at LCLS II is studied. The two-bunch beam dynamics, the THz wiggler and radiation are described, as well as the transport system bringing the THz pulses from the wiggler to the X-ray experimental hall., Experiments using a THz pump and an X-ray probe at an X-ray free-electron laser (XFEL) facility like the Linac Coherent Light Source II (LCLS II) require frequency-tunable (3 to 20 THz), narrow bandwidth (∼10%), carrier-envelope-phase-stable THz pulses that produce high fields (>1 MV cm−1) at the repetition rate of the X-rays and are well synchronized with them. In this paper, a two-bunch scheme to generate THz radiation at LCLS II is studied: the first bunch produces THz radiation in an electromagnet wiggler immediately following the LCLS II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in THz transport. The two-bunch beam dynamics, the THz wiggler and radiation are described, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.

All‐optical helicity‐dependent switching in ferromagnetic layers has revealed an unprecedented route to manipulate magnetic configurations by circularly polarized femtosecond laser pulses. In this work, rare‐earth free synthetic ferrimagnetic heterostructures made from two antiferromagnetically exchange coupled ferromagnetic layers are studied. Experimental results, supported by numerical simulations, show that the designed structures enable all‐optical switching which is controlled, not only by light helicity, but also by the relative Curie temperature of each ferromagnetic layer. Indeed, through the antiferromagnetic exchange coupling, the layer with the larger Curie temperature determines the final orientation of the other layer and so the synthetic ferrimagnet. For similar Curie temperatures, helicity‐independent back switching is observed and the final magnetic configuration is solely determined by the initial magnetic state. This demonstration of electrically‐detected, optical control of engineered rare‐earth free heterostructures opens a novel route toward practical opto‐spintronics., All‐optical helicity‐dependent switching in synthetic ferrimagnetic samples made of two exchanged coupled ferromagnetic layers is shown to depend on the respective Curie temperature of each layer. By varying the CoFeB layer thickness, its Curie temperature can be tuned. Consequently, the switching is set not only by the light helicity but also by the CoFeB thickness.

The optical design of a soft X-ray spectrometer that utilizes Wolter mirrors to enable imaging-mode spectroscopy with a beam-size independent spatial resolution in, for example, tandem catalysts in reaction is presented. When such a spectrometer is used in pump–probe experiments to study the transient electron dynamics, the imaging capability of the Wolter mirrors can offer femtosecond time delay between the pump and probe beams with non-collinear wavefronts., The optical design of a Hettrick–Underwood-style soft X-ray spectrometer with Wolter type 1 mirrors is presented. The spectrometer with a nominal length of 3.1 m can achieve a high resolving power (resolving power higher than 10000) in the soft X-ray regime when a small source beam (