Review of Scientific Instruments最新文献

We present the combination of a broadband terahertz time-domain spectroscopy system (0.1-8 THz), a diamond anvil cell (DAC) capable of generating high pressure conditions of up to 10 GPa, and a cryostat reaching temperatures as low as 10 K. This combination allows us to perform equilibrium and time-resolved THz spectroscopy measurements of a sample while continuously tuning its temperature and pressure conditions. In this study, the procedures and characterizations necessary to carry out such experiments in a tabletop setup are presented. Due to the large modifications of the terahertz beam as it goes through the DAC, standard terahertz time-domain spectroscopy analysis procedures are no longer applicable. New methods to extract the pressure dependent material parameters are presented, both for samples homogeneously filling the DAC sample chamber as well as for bulk samples embedded in pressure media. Different pressure media are tested and evaluated using these new methods, and the obtained material parameters are compared to literature values. Time resolved measurements under pressure are demonstrated using an optical pump-THz probe scheme.

High-voltage (HV) DC power supplies, defined here as sources providing DC output in the kilovolt range (typically a few to a few tens of kilovolts), are critical in scientific and industrial applications that demand low ripple, high efficiency, precise voltage regulation, and low stored energy. Achieving these requirements is challenging due to the significant parasitic elements of HV high-frequency transformers, such as leakage inductance (Lleak), reflected winding capacitance (Cp), and magnetizing inductance (Lp), which increase circulating currents and reduce efficiency. To address these challenges, this work proposed an optimal design methodology for a fourth-order LCLC resonant converter that gainfully integrates Lleak, Cp, and Lp into the resonant tank circuit. A steady-state analysis and design methodology is developed to ensure unity power factor (UPF) operation, soft-switching in entire load range (ZCS turn-onturn-off), and load-independent constant voltage output characteristics. In addition, a kVA/kW size optimization technique is presented to minimize stored reactive power at the optimal quality factor (Qs,opt=1/γ, where γ = Lp/Ls denotes the magnetizing to series inductance ratio. A scaled down -5 kV prototype validates the proposed research, demonstrating UPF operation, soft-switching, a peak efficiency of 97.26%, and ∼6.4% voltage regulation at 20% load, thereby confirming the validity of the theoretical analysis.

Circular dichroism spectroscopy is known to provide important insights into the interplay of different degrees of freedom in quantum materials, and yet spectroscopic study of the optoelectronic responses of quantum materials to structured optical fields, such as light with finite spin and orbital angular momentum, has not yet been widely explored, particularly at cryogenic temperature. Here, we demonstrate the design and application of a novel instrument that integrates scanning spectroscopic photocurrent measurements with structured light of controlled spin and orbital angular momentum. For structured photons with wavelengths between 500 and 700 nm, this instrument can perform spatially resolved photocurrent measurements of two-dimensional materials or thin crystals under magnetic fields up to ±14 T, at temperatures from 400 K down to 3 K, with either spin angular momentum ±h or orbital angular momentum ± ℓh (where ℓ = 1, 2, 3… is the topological charge), and over a (35 × 25) μm2 area with ∼1 μm spatial resolution when coupling with a f = 75 mm objective lens at 3 K. These capabilities of the instrument are exemplified by magneto-photocurrent spectroscopic measurements of monolayer 2H-MoS2 field-effect transistors, which not only reveal the excitonic spectra but also demonstrate monotonically increasing photocurrents with increasing |ℓ| and excitonic Zeeman splitting and an enhanced Landé g-factor due to the enhanced formation of intervalley dark excitons under magnetic field. These studies thus demonstrate the versatility of the scanning photocurrent spectrometry for investigating excitonic physics, optical selection rules, and optoelectronic responses of novel quantum materials and engineered quantum devices to structured light.

We have developed a new laser desorption scheme coupled to a supersonic expansion able to operate at several kHz rates. We demonstrate that it can be used to perform cold spectroscopy of flexible or fragile molecules. We also demonstrate its ability to study non-covalent complexes, such as hydrated molecules, which can be formed in the beam.

Levitated optical mechanical systems have demonstrated excellent force and impulse sensitivity and are currently being developed for the creation of non-classical states of motion in these new quantum systems. An important requirement in the design of these systems is the ability to independently control and cool all three translational degrees of freedom. Here, we describe the design and implementation of a stable and robust 3D velocity feedback cooling scheme with particular emphasis on creating minimal crosstalk between the independent oscillatory modes when cooling.

Hard x-rays generated by bremsstrahlung from low-energy electrons have a wide distribution of emission angles, which inherently limits radiation utilization efficiency. This study proposes a Compton-scattering-based augmentation technique that increases utilization efficiency by partially scattering laterally escaping photons into the detection region and reducing their average energy. The augmentation characteristics of various Compton scattering layer (CSL) materials and geometries were analyzed theoretically, validated numerically, and used to establish a practical selection method for CSL design. A graphite CSL tailored for a cylindrical virtual-cathode reflex triode array was developed and experimentally tested. The experimental data show a 13.9% increase in radiation utilization efficiency-consistent with the 13.5% predicted by simulation-and a 28.4% increase in uniform-dose area.

We present a custom sample holder system (SHS) enabling high-fidelity reflectance and transmittance ([R, T]) measurements of small (3-7 mm) diamond samples using dual-beam spectrophotometry. Through precision alignment, standard reference material-based correction strategies, and aperture-induced distortion cancellation, the SHS achieves sub-percent absolute photometric accuracy, allowing direct inversion of [R, T] for optical constants [n, k] via a Newton-Raphson (N-R) method. This process eliminates reliance on curve-fitting, instead using branch topology-physical (p-) and mathematical (m-) branch crossings-to extract thickness, roughness, and vertical non-uniformity from fringe behavior. Applied to boron-doped diamond (BDD) homoepitaxial films, the method reduces thickness variance by over 3× compared to mass-gain measurements and reveals carrier density gradients in thin layers consistent with secondary ion mass spectroscopy (SIMS). Notably, ripple-like discontinuities in [n, k]-often dismissed as artifacts-are shown to encode real growth physics. This enables optical retrieval of effective hole mass (∼0.48 m0), carrier lifetime, and depth-dependent doping profiles non-destructively and with nanoscale sensitivity. Beyond diamond, this approach reframes spectrophotometry not as a passive measurement but as an epistemic filter: a falsification engine that tests the adequacy of optical models. Inversion-aware metrology thus enables new modes of structural verification, diagnostic clarity, and growth-process insight across small-scale and high-optical density material systems.

In situ x-ray mirror surface figure metrology under vacuum and high heat loads is essential for monitoring deformations and enabling adaptive corrections. This study introduces a high-precision vacuum metrology system based on a pentaprism long trace profiler, designed to monitor clamping and thermal deformations while enabling adaptive wavefront corrections. The pentaprism and scanning stage are vacuum-internal, with an external detector to minimize window errors. Two different optical configurations were studied: the Internal Optical Path with External Detector (IOP-ED) configuration and the external optical head configuration. Vacuum evaluations improved to sub-0.1 μrad RMS slope repeatability, yielding 0.23 μrad RMS systematic errors for the IOP-ED configuration, with a scan range of 150 mm on a flat mirror at a vacuum level of 200 Pa. Future enhancements include full-vacuum integration to eliminate residual instabilities.

The 3ω technique is a prominent thermal conductivity measurement methodology for thin films, substrates, nanowires, and thermal boundary conductance. The extraction of the thermal conductivity typically relies on measuring the thermal response across a wide range of frequencies and determining the slope within acceptable limiting conditions, which can be a time-consuming process prone to error from the amplification of noise when taking the derivative of discrete temperature data to determine thermal conductivity. Here, we develop and demonstrate a frequency-modulated 3ω method (FM-3ω) with which we directly measure the derivative of the 3ω signal by varying the center frequency ω, eliminating the need to postprocess the data, thereby reducing the time to take such measurements from hours to minutes. Our modulation approach is a frequency modulation method in which the frequency ω of the excitation current is sinusoidally varied over time. We show that our new method produces results with similar accuracy to the traditional method on bulk sapphire and borofloat 33 samples, and we further explore the limitations of modulation depth and center frequency on the results. We find that thermal conductivity measurements from the FM-3ω method agree well with thermal conductivities extracted through linear fits to temperature data over similar frequency windows of the traditional method. Our method provides a new strategy using frequency modulation and tandem demodulation to directly measure the derivative of temperature, thus contributing to the advancement of thermal transport sciences by increasing the ease and pace of measuring the thermal conductivity of thin films and multilayer structures.