Review of Scientific Instruments最新文献

The world's strongest bio-based filament is currently produced from the wet spinning of cellulose nanofibrils. Such filaments could provide sustainable alternatives to currently available reinforcement fibers for high performance composites. Finding the weakest point of such filaments is of critical importance to their final application. However, what constitutes the weakest point in these filaments has yet to be determined with any certainty. Laser diffraction in conjunction with the Fraunhofer (single-slit) approximation could provide a rapid, nondestructive defectoscopy technique. Finding the thinnest point is the most accurate estimate of the breakpoint, with a mean distance-to-breakpoint of 1100 ± 200 μm, whereas the most precise determination of the weakest point is establishing which point is the least slit-like (48% of all cases). Combining width and propensity to be more or less slit-like was attempted to provide an accurate and precise metric ('the failure factor'). With an accuracy of 1000 ± 200 μm, this is the best possible estimate using the methodology presented here. The results indicate a need for further refinement of the method. Incorporating machine learning algorithms would increase reliability by circumventing the need for approximations. Performing high-resolution tomograms of the samples to take into account the cross-sectional circularity could be implemented as an additional in-depth secondary method. With the technique already presenting advantages in terms of speed and cost compared to other methods, e.g., electron microscopy, such instruments could be integrated into a production line, providing real-time defectoscopy and quality control.

We present a method and an accompanying data analysis technique that provide direct displacement information of surfaces based on optical beam deflection. This approach improves measurement accuracy by simplifying the measurement procedure and avoiding the need for optical system modeling. With calibration, the spatially dependent displacement of a surface becomes available. This method is applied to a circularly symmetric deformation of a gold-silicon nitride membrane heterostructure whose motion is excited by a modulated laser, and results are presented. The general approach is applicable to other deformation profiles with known features other than circular symmetry, making it broadly useful for characterizing the mechanical behavior of micro-scale devices and for optomechanics and mechanical metamaterial studies.

We report on a setup for photoluminescence (PL) spectroscopy, allowing to perform time resolved, steady-state, and spatially resolved PL and PL imaging. Time domain information (with ≈50 ps resolution) is achieved via time-correlated single photon counting (TCSPC), while the spectral information (in the ≈1-4 eV NIR-UV energy range) is accessed through a common-path interferometer based on birefringence, with the PL spectrum being retrieved via a Fourier transform approach. The micro-PL approach allows us to measure the PL signal of micron-sized samples, such as exfoliated 2D semiconductors. Moreover, the high efficiency of signal collection and analysis allows us to resolve weak PL signals from indirect-bandgap semiconductors. We measure the time-, frequency-, and spatially resolved PL on exfoliated flakes of WSe2, MoS2, and WS2 as examples to display the potential of our new apparatus.

Transient absorption (TA) is the most prominent method to observe relaxation dynamics in the toolbox of ultrafast spectroscopy. Within the framework of time-dependent perturbation theory, TA is a third-order technique as it relies on two interactions with the pump and one with the probe field. Since the advent of ultrafast TA, researchers have struggled to limit or better quantify the contributions of higher orders, such as the fifth order, as they will emerge along the same phase matching direction as the desired third order. Intensity cycling is a recently demonstrated experimental approach to isolate third from higher order signals. It requires transient absorption spectra at a minimum of three different intensities. This is experimentally challenging as the conditions for these three experiments need to be as similar as possible for a meaningful comparison. We present a solution to this problem based on a Sagnac-interferometer. Our design allows for shot-to-shot variations of pump pulse intensities. An entire intensity cycling dataset with 290 delay times for three different pump excitation densities is recorded within 30 min. We demonstrate the feasibility of our setup on a cyanine dye in solution.

Hefei Advanced Light Facility is a diffraction-limited synchrotron radiation light source in the soft x-ray range. The BL04 beamline needs micro-focusing spots for spatial and time-resolving experiments, and the Kirkpatrick-Baez mirror system is adopted as a post-focusing system. In this paper, a high-precision mirror bender with flexure mechanism modules has been designed to dynamically bend the flat mirror to an elliptical form. Given the required high surface accuracy, the mirror bender is optimized with the variable mirror profile. The bending moments can be applied independently on the bender ends, so the mirror can be bent to a different elliptical form, meeting the needs of focusing on different experimental stations. Based on the optomechanical design, the mirror bender can bend a 500 mm long flat mirror to an elliptical form with a small radius of curvature (∼400 m). When focused on the photo emission electron microscopy station, the residual slope error of the bent mirror surface is optimized to 7.2 nrad (rms). This work introduces the bender's optomechanical design and simulation process for verification. In addition, the machining and assembly errors' influence on the bending surface is evaluated and the influence of mirror substrate manufacturing errors on surface accuracy is systematically discussed. The tolerance requirements for mirror manufacturing are specified based on the analysis results. The optomechanical design and optimization for the bender provide a reference for subsequent engineering design.

To solve light loss from dead zones between Geiger-mode avalanche photodiode cells in silicon photomultipliers (SiPMs), this paper proposes a dead-zone light recovery scheme using focon/tapered fiber arrays. A microlens-like alignment method achieves precise fiber-SiPM integration. A multi-physics coupling simulation model compares light transmission and photoelectric response of original SiPM, tapered fiber-SiPM, and focon-SiPM under 13/25 μm cell sizes. Simulations show that under 300-1100 nm incident light, both structures significantly optimize SiPM performance: Tapered fibers boost average photocurrent by 70.19% and effective fill factor by 69.93% for 13 μm cells and 35.56%/33.84% for 25 μm cells. Focons show slightly lower improvements (68.77%/68.90% for 13 μm and 32.04%/30.84% for 25 μm). Neither scheme affects SiPM electrical stability. Tapered fibers excel in light recovery under small incident angles and wide bands, with applications in low-light detection (PET imaging, automotive light detection and ranging, and bioluminescence detection).

Perfect laser mode is required in many research fields such as quantum computing and precision measurement. Fiber optics provides a useful tool for maintaining a high quality laser when transmitting the laser over a long distance. Fiber link between modular structures of complicated optical paths increases the effectiveness and robustness of the optical experiment. It is a key element in coupling the laser into fiber with high efficiency in fiber optics applications. However, in confined or vacuum environments, such as spacecraft cabins, manual alignment is nearly impossible, highlighting the need for automated solutions. In this study, we experimentally investigated several automatic coupling algorithms, including the iterative scanning method and three global optimization algorithms. The results show that Bayesian optimization, by exploiting multidimensional control and high-precision actuation, enabled the coupling efficiency to reach its maximum of higher than 93% within 10 s. These algorithms provide repeatable and high-precision fiber alignment solutions for all-optical experiments under different conditions.

Electric-Field-Induced Lyman-α Emission is a promising technique to measure the electric field strength in a plasma. It relies on a beam of metastable hydrogen atoms and the subsequent emission of Lyman-α radiation when atoms are quenched by the electric field. We present a four-level population kinetics model that accounts for both Stark and Zeeman effects, extending previous approaches limited to purely electric fields. The model is employed to predict the Lyman-α emission from a 500 eV hydrogen beam moving through a known configuration of electric and magnetic fields. An excellent agreement is found between the calculated and experimentally measured signals.

Lateral spatial resolution (LSR) is a key parameter of confocal Raman microscopy, determining the system's ability to resolve fine structural and chemical details at micro- to nanoscales. This study introduces a quantitative method to determine the LSR of a confocal Raman microscope using cross-edge one-dimensional Raman scan measurements of the area-sensitive G mode and edge-length-sensitive D mode intensity profiles at graphene edges. The measured LSR values for an objective with numerical aperture (NA) of 0.90 approach diffraction-limited estimates when the pinhole size is close to zero; however, LSR measurements with large confocal apertures yield values significantly larger than diffraction-limited predictions, as confirmed by measurements across objectives with varying NAs (NA = 0.25-0.90). The results demonstrate that achieving optimal resolution requires precise laser focusing, appropriate pinhole size selection, and beam expansion matching the objective's entrance pupil, while defocusing or reduced beam diameter degrades performance. This method provides a practical and quantitative approach for LSR evaluation in confocal Raman microscopy, applicable to diverse experimental conditions.

A platform for multi-GHz frame rate imaging using a single intensified gating camera that relies on staggered optical delays in high-resolution optical fibers is introduced. The diagnostic consists of a beam splitter assembly that partitions the image, varying-length high-resolution optical fibers that stagger the image in time, and a gated camera that simultaneously images the fiber outputs. The time delay of the fibers is calibrated using a laser pulser and a fast photodiode. Individual channels are rotated due to the orientation of their respective fibers and may be flipped in the beam splitter assembly, so a simple post-processing technique is used to extract the frames. An eight-channel, 4 GHz frame rate version of this diagnostic was constructed using an intensified charge-coupled device (ICCD) with 3 ns gate times and was fielded to image visible light emission from a developing high voltage vacuum flashover event. Potential improvements or variations in this diagnostic to achieve a range of imaging capabilities for pulsed power plasmas are discussed.