Showing papers in "Review of Scientific Instruments in 2019"

The qPlus sensor, a powerful core for the atomic force microscope

Abstract: Atomic force microscopy (AFM) was introduced in 1986 and has since made its way into surface science, nanoscience, chemistry, biology, and material science as an imaging and manipulating tool with a rising number of applications. AFM can be employed in ambient and liquid environments as well as in vacuum and at low and ultralow temperatures. The technique is an offspring of scanning tunneling microscopy (STM), where the tunneling tip of the STM is replaced by using a force sensor with an attached tip. Measuring the tiny chemical forces that act between the tip and the sample is more difficult than measuring the tunneling current in STM. Therefore, even 30 years after the introduction of AFM, progress in instrumentation is substantial. Here, we focus on the core of the AFM, the force sensor with its tip and detection mechanism. Initially, force sensors were mainly micro-machined silicon cantilevers, mainly using optical methods to detect their deflection. The qPlus sensor, originally based on a quartz tuning fork and now custom built from quartz, is self-sensing by utilizing the piezoelectricity of quartz. The qPlus sensor allows us to perform STM and AFM in parallel, and the spatial resolution of its AFM channel has reached the subatomic level, exceeding the resolution of STM. Frequency modulation AFM (FM-AFM), where the frequency of an oscillating cantilever is altered by the gradient of the force that acts between the tip and the sample, has emerged over the years as the method that provides atomic and subatomic spatial resolution as well as force spectroscopy with sub-piconewton sensitivity. FM-AFM is precise; because of all physical observables, time and frequency can be measured by far with the greatest accuracy. By design, FM-AFM clearly separates conservative and dissipative interactions where conservative forces induce a frequency shift and dissipative interactions alter the power needed to maintain a constant oscillation amplitude of the cantilever. As it operates in a noncontact mode, it enables simultaneous AFM and STM measurements. The frequency stability of quartz and the small oscillation amplitudes that are possible with stiff quartz sensors optimize the signal to noise ratio. Here, we discuss the operating principles, the assembly of qPlus sensors, amplifiers, limiting factors, and applications. Applications encompass unprecedented subatomic spatial resolution, the measurement of forces that act in atomic manipulation, imaging and spectroscopy of spin-dependent forces, and atomic resolution of organic molecules, graphite, graphene, and oxides.

High-density diffuse optical tomography for imaging human brain function.

Abstract: This review describes the unique opportunities and challenges for noninvasive optical mapping of human brain function. Diffuse optical methods offer safe, portable, and radiation free alternatives to traditional technologies like positron emission tomography or functional magnetic resonance imaging (fMRI). Recent developments in high-density diffuse optical tomography (HD-DOT) have demonstrated capabilities for mapping human cortical brain function over an extended field of view with image quality approaching that of fMRI. In this review, we cover fundamental principles of the diffusion of near infrared light in biological tissue. We discuss the challenges involved in the HD-DOT system design and implementation that must be overcome to acquire the signal-to-noise necessary to measure and locate brain function at the depth of the cortex. We discuss strategies for validation of the sensitivity, specificity, and reliability of HD-DOT acquired maps of cortical brain function. We then provide a brief overview of some clinical applications of HD-DOT. Though diffuse optical measurements of neurophysiology have existed for several decades, tremendous opportunity remains to advance optical imaging of brain function to address a crucial niche in basic and clinical neuroscience: that of bedside and minimally constrained high fidelity imaging of brain function.

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Abstract: Time- and angle-resolved photoemission spectroscopy (trARPES) employing a 500 kHz extreme-ultraviolet light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification, and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of more than 1011 photons/s on the sample. Combined with a state-of-the-art ARPES chamber, this table-top experiment allows high-repetition rate pump-probe experiments of electron dynamics in occupied and normally unoccupied (excited) states in the entire Brillouin zone and with a temporal system response function below 40 fs.

SpraySyn-A standardized burner configuration for nanoparticle synthesis in spray flames.

Abstract: In many scientific communities, the definition of standardized experiments has enabled major progress in process understanding. The investigation of the spray-flame synthesis of nanoparticles at a well-defined standard burner by experiment and simulation makes it possible to produce a comprehensive data set with various established and novel measuring methods. In this work, we introduce the design of the SpraySyn burner as a new standard for a free-jet type burner that offers well-defined and simulation-friendly boundary conditions and geometries as well as accessibility for optical diagnostics. A combustible precursor solution is fed through a centrally located capillary and aerosolized with an oxygen dispersion gas flow. The spray flame is stabilized by a premixed flat methane/oxygen pilot flame fed via a porous bronze matrix surrounded by a stabilizing nitrogen coflow emanating through the same porous matrix, providing easy-to-calculate boundary conditions for simulations. This burner design enables the use of a wide choice of solvents, precursors, and precursor combinations. Best-practice operating instructions and parameters are given, and large-eddy simulations are performed demonstrating the suitability of the SpraySyn burner for computational fluid dynamics simulations. For ensuring reproducible operation across labs, we define a consumer-camera-based flame characterization scheme for the quantitative assessment of the flame geometry such as flame length, diameter, tilt angle, and photometric distribution of visible chemiluminescence along the center axis. These parameters can be used for benchmarking the pilot and spray flame by each user of the SpraySyn burner with the reference flames.

An improved laboratory-based x-ray absorption fine structure and x-ray emission spectrometer for analytical applications in materials chemistry research

Abstract: X-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) are advanced x-ray spectroscopies that impact a wide range of disciplines. However, unlike the majority of other spectroscopic methods, XAFS and XES are accompanied by an unusual access model, wherein the dominant use of the technique is for premier research studies at world-class facilities, i.e., synchrotron x-ray light sources. In this paper, we report the design and performance of an improved XAFS and XES spectrometer based on the general conceptual design of Seidler et al. [Rev. Sci. Instrum. 85, 113906 (2014)]. New developments include reduced mechanical degrees of freedom, much-increased flux, and a wider Bragg angle range to enable extended x-ray absorption fine structure (EXAFS) measurement and analysis for the first time with this type of modern laboratory XAFS configuration. This instrument enables a new class of routine applications that are incompatible with the mission and access model of the synchrotron light sources. To illustrate this, we provide numerous examples of x-ray absorption near edge structure (XANES), EXAFS, and XES results for a variety of problems and energy ranges. Highlights include XAFS and XES measurements of battery electrode materials, EXAFS of Ni with full modeling of results to validate monochromator performance, valence-to-core XES for 3d transition metal compounds, and uranium XANES and XES for different oxidation states. Taken en masse, these results further support the growing perspective that modern laboratory-based XAFS and XES have the potential to develop a new branch of analytical chemistry.

A steady-state thermoreflectance method to measure thermal conductivity

Abstract: We demonstrate a steady-state thermoreflectance-based optical pump-probe technique to measure the thermal conductivity of materials using a continuous wave laser heat source. The technique works in principle by inducing a steady-state temperature rise in a material via long enough exposure to heating from a pump laser. A probe beam is then used to detect the resulting change in reflectance, which is proportional to the change in temperature at the sample surface. Increasing the power of the pump beam to induce larger temperature rises, Fourier’s law is used to determine the thermal conductivity. We show that this technique is capable of measuring the thermal conductivity of a wide array of materials having thermal conductivities ranging from 1 to >2000 W m−1 K−1, in excellent agreement with literature values.

A microfocus x-ray computed tomography based gas hydrate triaxial testing apparatus.

Abstract: Gas hydrate-bearing sediment shows complex mechanical characteristics. Its macroscopic deformation process involves many microstructural changes such as phase transformation, grain transport, and cementation failure. However, the conventional gas hydrate triaxial testing apparatus is not possible to obtain the microstructure in the samples. In this study, a novel, low-temperature (-35 to 20 °C), high-pressure (>16 MPa confining pressure and >95.4 MPa vertical stress) triaxial testing apparatus suitable for X-ray computed tomography scanning is developed. The new apparatus permits time-lapse imaging to capture the role of hydrate saturation, effective stress, strain rate, hydrate decomposition on hydrate-bearing sediment characteristic, and cementation failure behavior. The apparatus capabilities are demonstrated using in situ generation of hydrate on a xenon hydrate-bearing glass bead sample. In the mentioned case, a consolidated drained shear test was conducted, and the imaging reveals hydrate occurrence with a saturation of 37.3% as well as the evolution of localized strain (or shear band) and cementation failure along with axial strain.

A direct comparison of high-speed methods for the numerical Abel transform.

Abstract: The Abel transform is a mathematical operation that transforms a cylindrically symmetric three-dimensional (3D) object into its two-dimensional (2D) projection. The inverse Abel transform reconstructs the 3D object from the 2D projection. Abel transforms have wide application across numerous fields of science, especially chemical physics, astronomy, and the study of laser-plasma plumes. Consequently, many numerical methods for the Abel transform have been developed, which makes it challenging to select the ideal method for a specific application. In this work, eight published transform methods have been incorporated into a single, open-source Python software package (PyAbel) to provide a direct comparison of the capabilities, advantages, and relative computational efficiency of each transform method. Most of the tested methods provide similar, high-quality results. However, the computational efficiency varies across several orders of magnitude. By optimizing the algorithms, we find that some transform methods are sufficiently fast to transform 1-megapixel images at more than 100 frames per second on a desktop personal computer. In addition, we demonstrate the transform of gigapixel images.

Cavity-enhanced high harmonic generation for extreme ultraviolet time- and angle-resolved photoemission spectroscopy.

Abstract: With its direct correspondence to electronic structure, angle-resolved photoemission spectroscopy (ARPES) is a ubiquitous tool for the study of solids. When extended to the temporal domain, time-resolved (TR)-ARPES offers the potential to move beyond equilibrium properties, exploring both the unoccupied electronic structure as well as its dynamical response under ultrafast perturbation. Historically, ultrafast extreme ultraviolet sources employing high-order harmonic generation (HHG) have required compromises that make it challenging to achieve a high energy resolution—which is highly desirable for many TR-ARPES studies—while producing high photon energies and a high photon flux. We address this challenge by performing HHG inside a femtosecond enhancement cavity, realizing a practical source for TR-ARPES that achieves a flux of over 1011 photons/s delivered to the sample, operates over a range of 8–40 eV with a repetition rate of 60 MHz. This source enables TR-ARPES studies with a temporal and energy resolution of 190 fs and 22 meV, respectively. To characterize the system, we perform ARPES measurements of polycrystalline Au and MoTe2, as well as TR-ARPES studies on graphite.

6 Gbps real-time optical quantum random number generator based on vacuum fluctuation.

Abstract: We demonstrate a 6 Gbps real-time optical quantum random number generator by measuring vacuum fluctuation. To address the common problem that speed gap exists between fast randomness generation and slow randomness extraction in most high-speed real-time quantum random number generator systems, we present an optimized extraction algorithm based on parallel implementation of Toeplitz hashing to reduce the influence of classical noise due to the imperfection of devices. Notably, the real-time rate of randomness extraction we have achieved reaches the highest speed of 12 Gbps by occupying less computing resources, and the algorithm has the ability to support hundreds of Gbps randomness extraction. By assuming that the eavesdropper with complete knowledge of the classical noise, our generator has a randomness generation speed of 6.83 Gbps and this supports the generation of 6 Gbps information-theoretically provable quantum random numbers, which are output in real-time through peripheral component interconnect express interface.

The upgraded Polaris powder diffractometer at the ISIS neutron source.

Abstract: This paper describes the design and operation of the Polaris time-of-flight powder neutron diffractometer at the ISIS pulsed spallation neutron source, Rutherford Appleton Laboratory, UK. Following a major upgrade to the diffractometer in 2010–2011, its detector provision now comprises five large ZnS scintillator-based banks, covering an angular range of 6° ≤ 2θ ≤ 168°, with only minimal gaps between each bank. These detectors have a substantially increased solid angle coverage (Ω ∼ 5.67 sr) compared to the previous instrument (Ω ∼ 0.82 sr), resulting in increases in count rate of between 2× and 10×, depending on 2θ angle. The benefits arising from the high count rates achieved are illustrated using selected examples of experiments studying small sample volumes and performing rapid, time-resolved investigations. In addition, the enhanced capabilities of the diffractometer in the areas of in situ studies (which are facilitated by the installation of a novel design of radial collimator around the sample position and by a complementary programme of advanced sample environment developments) and in total scattering studies (to probe the nature of short-range atomic correlations within disordered crystalline solids) are demonstrated.This paper describes the design and operation of the Polaris time-of-flight powder neutron diffractometer at the ISIS pulsed spallation neutron source, Rutherford Appleton Laboratory, UK. Following a major upgrade to the diffractometer in 2010–2011, its detector provision now comprises five large ZnS scintillator-based banks, covering an angular range of 6° ≤ 2θ ≤ 168°, with only minimal gaps between each bank. These detectors have a substantially increased solid angle coverage (Ω ∼ 5.67 sr) compared to the previous instrument (Ω ∼ 0.82 sr), resulting in increases in count rate of between 2× and 10×, depending on 2θ angle. The benefits arising from the high count rates achieved are illustrated using selected examples of experiments studying small sample volumes and performing rapid, time-resolved investigations. In addition, the enhanced capabilities of the diffractometer in the areas of in situ studies (which are facilitated by the installation of a novel design of radial collimator around the sample pos...

A setup for extreme-ultraviolet ultrafast angle-resolved photoelectron spectroscopy at 50-kHz repetition rate.

Abstract: Time- and angle-resolved photoelectron spectroscopy (trARPES) is a powerful method to track the ultrafast dynamics of quasiparticles and electronic bands in energy and momentum space. We present a setup for trARPES with 22.3 eV extreme-ultraviolet (XUV) femtosecond pulses at 50-kHz repetition rate, which enables fast data acquisition and access to dynamics across momentum space with high sensitivity. The design and operation of the XUV beamline, pump-probe setup, and ultra-high vacuum endstation are described in detail. By characterizing the effect of space-charge broadening, we determine an ultimate source-limited energy resolution of 60 meV, with typically 80-100 meV obtained at 1-2 × 1010 photons/s probe flux on the sample. The instrument capabilities are demonstrated via both equilibrium and time-resolved ARPES studies of transition-metal dichalcogenides. The 50-kHz repetition rate enables sensitive measurements of quasiparticles at low excitation fluences in semiconducting MoSe2, with an instrumental time resolution of 65 fs. Moreover, photo-induced phase transitions can be driven with the available pump fluence, as shown by charge density wave melting in 1T-TiSe2. The high repetition-rate setup thus provides a versatile platform for sensitive XUV trARPES, from quenching of electronic phases down to the perturbative limit.

The Velociprobe: An ultrafast hard X-ray nanoprobe for high-resolution ptychographic imaging.

Abstract: Motivated by the advanced photon source upgrade, a new hard X-ray microscope called "Velociprobe" has been recently designed and built for fast ptychographic imaging with high spatial resolution. We are addressing the challenges of high-resolution and fast scanning with novel hardware designs, advanced motion controls, and new data acquisition strategies, including the use of high-bandwidth interferometric measurements. The use of granite, air-bearing-supported stages provides the necessary long travel ranges for coarse motion to accommodate real samples and variable energy operation while remaining highly stable during fine scanning. Scanning the low-mass zone plate enables high-speed and high-precision motion of the probe over the sample. With an advanced control algorithm implemented in a closed-loop feedback system, the setup achieves a position resolution (3σ) of 2 nm. The instrument performance is evaluated by 2D fly-scan ptychography with our developed data acquisition strategies. A spatial resolution of 8.8 nm has been demonstrated on a Au test sample with a detector continuous frame rate of 200 Hz. Using a higher flux X-ray source provided by double-multilayer monochromator, we achieve 10 nm resolution for an integrated circuit sample in an ultrafast scan with a detector's full continuous frame rate of 3000 Hz (0.33 ms per exposure), resulting in an outstanding imaging rate of 9 × 104 resolution elements per second.

Unifying obstacle detection, recognition, and fusion based on millimeter wave radar and RGB-depth sensors for the visually impaired.

Abstract: It is very difficult for visually impaired people to perceive and avoid obstacles at a distance. To address this problem, the unified framework of multiple target detection, recognition, and fusion is proposed based on the sensor fusion system comprising a low-power millimeter wave (MMW) radar and an RGB-Depth (RGB-D) sensor. In this paper, the Mask R-CNN and the single shot multibox detector network are utilized to detect and recognize the objects from color images. The obstacles' depth information is obtained from the depth images using the MeanShift algorithm. The position and velocity information on the multiple target is detected by the MMW radar based on the principle of a frequency modulated continuous wave. The data fusion based on the particle filter obtains more accurate state estimation and richer information by fusing the detection results from the color images, depth images, and radar data compared with using only one sensor. The experimental results show that the data fusion enriches the detection results. Meanwhile, the effective detection range is expanded compared to using only the RGB-D sensor. Moreover, the data fusion results keep high accuracy and stability under diverse range and illumination conditions. As a wearable system, the sensor fusion system has the characteristics of versatility, portability, and cost-effectiveness.

Automated image processing method to quantify rotating detonation wave behavior.

Abstract: An image processing technique is developed to automatically determine both average and instantaneous detonation wave properties within a rotating detonation rocket engine (RDRE) using high-speed imaging. This method entails segmenting the imaged RDRE annulus into 200 azimuthal bins and tracking integrated pixel intensity in each bin. By combining individual pixel intensity temporal histories across the azimuthal bins, this provides what is termed a detonation surface that visualizes the propagation of the individual detonation fronts azimuthally around the annulus. Average detonation modal properties including wave speed Ūwv, operational frequency fdet, and the number of waves m are determined automatically through a two-dimensional Fourier analysis of the detonation surface data. Also, instantaneous wave speeds Uwv for each individual detonation are determined by taking the numerical derivative of each waves’ angular position temporal history from the detonation surface. This provides useful insight into wave-to-wave variability for an operating condition, as well as denoting modal transitions and mode stability. For the flow conditions investigated, the number of waves ranges from 2 to 14, with Ūwv varying between 900 and 1700 m/s, corresponding to 33%–71% of the ideal Chapman-Jouguet detonation speed; these modes exhibit an operational frequency of 20–45 kHz, with an average of 40 kHz. Overall, these measurements advance the understanding of RDRE’s and may lead to performance gains above those achievable from constant pressure engines.

Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10-1.

Abstract: We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resolution, high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a maximum detection solid angle of 2 × 10-3 sr. The energy resolution of all pixels combined is 1.5 eV full width at half maximum at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resolution and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering experiments obtained with the spectrometer are presented.

Magnetic field stabilization system for atomic physics experiments.

Abstract: Atomic physics experiments commonly use millitesla-scale magnetic fields to provide a quantization axis. As atomic transition frequencies depend on the magnitude of this field, many experiments require a stable absolute field. Most setups use electromagnets, which require a power supply stability not usually met by commercially available units. We demonstrate the stabilization of a field of 14.6 mT to 4.3 nT rms noise (0.29 ppm), compared to noise of >100 nT without any stabilization. The rms noise is measured using a field-dependent hyperfine transition in a single 43Ca+ ion held in a Paul trap at the center of the magnetic field coils. For the 43Ca+ "atomic clock" qubit transition at 14.6 mT, which depends on the field only in second order, this would yield a projected coherence time of many hours. Our system consists of a feedback loop and a feedforward circuit that control the current through the field coils and could easily be adapted to other field amplitudes, making it suitable for other applications such as neutral atom traps.

Upgrade to the MAPS neutron time-of-flight chopper spectrometer.

Abstract: The MAPS direct geometry time-of-flight chopper spectrometer at the ISIS pulsed neutron and muon source has been in operation since 1999, and its novel use of a large array of position-sensitive neutron detectors paved the way for a later generations of chopper spectrometers around the world. Almost two decades of experience of user operations on MAPS, together with lessons learned from the operation of new generation instruments, led to a decision to perform three parallel upgrades to the instrument. These were to replace the primary beamline collimation with supermirror neutron guides, to install a disk chopper, and to modify the geometry of the poisoning in the water moderator viewed by MAPS. Together, these upgrades were expected to increase the neutron flux substantially, to allow more flexible use of repetition rate multiplication and to reduce some sources of background. Here, we report the details of these upgrades and compare the performance of the instrument before and after their installation as well as to Monte Carlo simulations. These illustrate that the instrument is performing in line with, and in some respects in excess of, expectations. It is anticipated that the improvement in performance will have a significant impact on the capabilities of the instrument. A few examples of scientific commissioning are presented to illustrate some of the possibilities.

Laser heating setup for diamond anvil cells for in situ synchrotron and in house high and ultra-high pressure studies

Abstract: The diamond anvil cell (DAC) technique combined with laser heating is one of the major methods for studying materials at high pressure and high temperature conditions. In this work, we present a transferable double-sided laser heating setup for DACs with in situ temperature determination. The setup allows precise heating of samples inside a DAC at pressures above 200 GPa and could be combined with synchrotron beamline equipment. It can be applied to X-ray diffraction and X-ray transmission microscopy experiments. In the setup, we use high-magnification and low working distance infinity corrected laser focusing objectives that enable us to decrease the size of the laser beam to less than 5 µm and achieve the maximum optical magnification of 320 times. All optical components of the setup were chosen to minimize chromatic and spatial aberrations for accurate in situ temperature determination by multiwavelength spectroscopy in the 570–830 nm spectral range. Flexible design of our setup allows simple interchange of laser sources and focusing optics for application in different types of studies. The setup was successfully tested in house and at the high-pressure diffraction beamline ID15B at the European Synchrotron Radiation Facility. We demonstrate an example of application of the setup for the high pressure–high temperature powder diffraction study of PdH and X-ray transmission microscopy of platinum at 22(1) GPa as a novel method of melting detection in DACs.

Towards a transportable aluminium ion quantum logic optical clock

Abstract: With the advent of optical clocks featuring fractional frequency uncertainties on the order of 10−17 and below, new applications such as chronometric leveling with few-centimeter height resolution emerge. We are developing a transportable optical clock based on a single trapped aluminum ion, which is interrogated via quantum logic spectroscopy. We employ singly charged calcium as the logic ion for sympathetic cooling, state preparation, and readout. Here, we present a simple and compact physics and laser package for manipulation of 40Ca+. Important features are a segmented multilayer trap with separate loading and probing zones, a compact titanium vacuum chamber, a near-diffraction-limited imaging system with high numerical aperture based on a single biaspheric lens, and an all-in-fiber 40Ca+ repump laser system. We present preliminary estimates of the trap-induced frequency shifts on 27Al+, derived from measurements with a single calcium ion. The micromotion-induced second-order Doppler shift for 27Al+ has been determined to be δνEMMν=−0.4−0.3+0.4×10−18 and the black-body radiation shift is δνBBR/ν = (−4.0 ± 0.4) × 10−18. Moreover, heating rates of 30 (7) quanta per second at trap frequencies of ωrad,Ca+ ≈ 2π × 2.5 MHz (ωax,Ca+ ≈ 2π × 1.5 MHz) in radial (axial) direction have been measured, enabling interrogation times of a few hundreds of milliseconds.

A high-pressure x-ray photoelectron spectroscopy instrument for studies of industrially relevant catalytic reactions at pressures of several bars

Abstract: We present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures of multiple bars. The instrument builds aroun ...

Resonant ultrasound spectroscopy: The essential toolbox.

Abstract: Resonant Ultrasound Spectroscopy (RUS) is an ultrasound-based minimal-effort high-accuracy elastic modulus measurement technique. RUS as described here uses the mechanical resonances (normal modes of vibration or just modes) of rectangular parallelepiped or cylindrical specimens with a dimension of from a fraction of a millimeter to as large as will fit into the apparatus. Provided here is all that is needed so that the reader can construct and use a state-of-the-art RUS system. Included are links to open-source circuit diagrams, links to download Los Alamos National Laboratory open-source data acquisition software, links to request free analysis software, procedures for acquiring measurements, considerations on building transducers, 3-D printed stage designs, and a full mathematical explanation of how the analysis software extracts elastic moduli from resonances.

Vibration isolation with high thermal conductance for a cryogen-free dilution refrigerator

Abstract: We present the design and implementation of a mechanical low-pass filter vibration isolation used to reduce the vibrational noise in a cryogen-free dilution refrigerator operated at 10 mK, intended for scanning probe techniques. We discuss the design guidelines necessary to meet the competing requirements of having a low mechanical stiffness in combination with a high thermal conductance. We demonstrate the effectiveness of our approach by measuring the vibrational noise levels of an ultrasoft mechanical resonator positioned above a superconducting quantum interference device. Starting from a cryostat base temperature of 8 mK, the vibration isolation can be cooled to 10.5 mK, with a cooling power of 113 µW at 100 mK. We use the low vibrations and low temperature to demonstrate an effective cantilever temperature of less than 20 mK. This results in a force sensitivity of less than 500 zN/Hz and an integrated frequency noise as low as 0.4 mHz in a 1 Hz measurement bandwidth.

Closed-cycle, low-vibration 4 K cryostat for ion traps and other applications

Abstract: In vacuo cryogenic environments are ideal for applications requiring both low temperatures and extremely low particle densities. This enables reaching long storage and coherence times, for example, in ion traps, essential requirements for experiments with highly charged ions, quantum computation, and optical clocks. We have developed a novel cryostat continuously refrigerated with a pulse-tube cryocooler and providing the lowest vibration level reported for such a closed-cycle system with 1 W cooling power for a <5 K experiment. A decoupling system suppresses vibrations from the cryocooler by three orders of magnitude down to a level of 10 nm peak amplitudes in the horizontal plane. Heat loads of about 40 W (at 45 K) and 1 W (at 4 K) are transferred from an experimental chamber, mounted on an optical table, to the cryocooler through a vacuum-insulated massive 120 kg inertial copper pendulum. The 1.4 m long pendulum allows installation of the cryocooler in a separate, acoustically isolated machine room. At the experimental chamber, we measured the residual vibrations using an interferometric setup. The positioning of the 4 K elements is reproduced to better than a few micrometer after a full thermal cycle to room temperature. Extreme high vacuum on the 10-15 mbar level is achieved. In collaboration with the Max-Planck-Institut fur Kernphysik, such a setup is now in operation at the Physikalisch-Technische Bundesanstalt for a next-generation optical clock experiment using highly charged ions.

The laser shock station in the dynamic compression sector. I.

Abstract: The Laser Shock Station in the Dynamic Compression Sector (DCS) [Advanced Photon Source (APS), Argonne National Laboratory] links a laser-driven shock compression platform with high energy x-ray pulses from the APS to achieve in situ, time-resolved x-ray measurements (diffraction and imaging) in materials subjected to well-characterized, high stress, short duration shock waves. This station and the other DCS experimental stations provide a unique and versatile facility to study condensed state phenomena subjected to shocks with a wide range of amplitudes (to above ∼350 GPa) and time-durations (∼10 ns-1 µs). The Laser Shock Station uses a 100 J, 5-17 ns, 351 nm frequency tripled Nd:glass laser with programmable pulse shaping and focal profile smoothing for maximum precision. The laser can operate once every 30 min. The interaction chamber has multiple diagnostic ports, a sample holder to expose 14 samples without breaking vacuum, can vary the angle between the x-ray and laser beams by 135°, and can translate to select one of the two types of x-ray beams. The x-ray measurement temporal resolution is ∼90 ps. The system is capable of reproducible, well-characterized experiments. In a series of 10 shots, the absolute variation in shock breakout times was less than 500 ps. The variation in peak particle velocity at the sample/window interface was 4.3%. This paper describes the entire DCS Laser Shock Station, including sample fabrication and diagnostics, as well as experimental results from shock compressed tantalum that demonstrate the facility's capability for acquiring high quality x-ray diffraction data.

A system for the synthesis of nanoparticles by laser ablation in liquid that is remotely controlled with PC or smartphone.

Abstract: Nanoparticles find applications in multiple technological and scientific fields, and laser ablation in liquid (LAL) emerged as a versatile method for providing colloidal solutions of nanomaterials with various composition, by a low cost, simple, self-standing, and "green" procedure. However, the use of high energy and high power laser beams is harmful, especially when coupled with flammable or toxic liquids, and in situ operation is required for starting, monitoring the LAL synthesis, and stopping it at the desired point. Here we describe the hardware and software design and the test results of a system for the production of nanoparticles by laser ablation synthesis in liquid solution (LASiS), which is remotely controllable with a personal computer or a smartphone. In this system, laser energy and solution flux are selectable, and the synthesis status can be monitored and managed at any time off site. Only commercially available components and software are employed, making the whole apparatus easily reproducible in any LAL laboratory. The system has proven its reliability in various conditions, including intercontinental remote control experiments. Overall, this apparatus represents a step forward to improve the safety and to more efficiently exploit the time of people working with LASiS, thus contributing to the increasing demand for off-site real time monitoring of experimental equipment in many scientific and industrial laboratories, due to safety and efficiency requirements.

MANTIS: A real-time quantitative multispectral imaging system for fusion plasmas

Abstract: This work presents a novel, real-time capable, 10-channel Multispectral Advanced Narrowband Tokamak Imaging System installed on the TCV tokamak, MANTIS. Software and hardware requirements are presented together with the complete system architecture. The image quality of the system is assessed with emphasis on effects resulting from the narrowband interference filters. Some filters are found to create internal reflection images that are correlated with the filters’ reflection coefficient. This was measured for selected filters where significant absorption (up to 65% within ∼70 nm of the filter center) was measured. The majority of this was attributed to the filter’s design, and several filters’ performance is compared. Tailored real-time algorithms exploiting the system’s capabilities are presented together with benchmarks comparing polling and event based synchronization. The real-time performance is demonstrated with a density ramp discharge performed on TCV. The behavior of spectral lines’ emission from different plasma species and their interpretation are qualitatively described.

A high-performance compact magnetic shield for optically pumped magnetometer-based magnetoencephalography.

Abstract: The rapid development of the optically pumped magnetometer (OPM) has offered a much more flexible method for magnetoencephalography (MEG). Without using liquid helium and its associated dewar device in the OPM detectors, the large and expensive magnetically shielded room (MSR) for traditional MEG systems could be replaced by a compact shield. In the present work, an economic and compact cylindrical shield was designed and built to meet the low-field working requirement of the OPM in detecting human brain neuronal activities. The performance of the compact shield was evaluated and further compared with that of a commercial MSR. Our results showed that the residual magnetic fields and background noise of the compact shield were lower than or comparable to those of the MSR. The remnant field in the shield is found to be 4.2 nT, a factor of 13 000 smaller than the geomagnetic field which is applied to the transverse direction of the shield, and the longitudinal shielding factors measured using a known alternating-current magnetic field are approximately 191, 205, and 3130 at 0.1 Hz, 1 Hz, and 10 Hz, respectively; in addition, the evoked dynamic waveforms in the human auditory cortex that were recorded separately in these two shields demonstrated consistency. Our findings suggested that a compact shield is feasible for OPM-based MEG applications with high performance and low cost.

Characterizing atomic magnetic gradiometers for fetal magnetocardiography.

Abstract: Atomic magnetometers (AMs) offer many advantages over superconducting quantum interference devices due to, among other things, having comparable sensitivity while not requiring cryogenics. One of the major limitations of AMs is the challenge of configuring them as gradiometers. We report the development of a spin-exchange relaxation free vector atomic magnetic gradiometer with a sensitivity of 3 fT cm−1 Hz−1/2 and common mode rejection ratio >150 in the band from DC to 100 Hz. We introduce a background suppression figure of merit for characterizing the performance of gradiometers. It allows for optimally setting the measurement baseline and for quickly assessing the advantage, if any, of performing a measurement in a gradiometric mode. As an application, we consider the problem of fetal magnetocardiography (fMCG) detection in the presence of a large background maternal MCG signal.

J-NSE-Phoenix, a neutron spin-echo spectrometer with optimized superconducting precession coils at the MLZ in Garching

Abstract: A novel set of superconducting main precession coils has been built and installed in the Julich-neutron spin-echo (J-NSE) spectrometer at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. These unique new coils comprise a field-integral optimizing field shape, fringe field compensation, and high stability. They yield an enhancement of a factor of 2.5 in the intrinsic field-integral homogeneity, i.e., the resolution. The coil concept has been developed for the ESSENSE instrument proposal for the European Spallation Source. We report on the construction of and on the first results from the new superconducting neutron spin-echo spectrometer at the MLZ in Garching where the coils are the main part of a refurbishment of the J-NSE spectrometer after twenty years of operation.