Serupweber8601

We design and develop a scanning probe microscope (SPM) system based on the qPlus sensor for atomic-scale optical experiments. The microscope operates under ultrahigh vacuum and low temperature (6.2 K). In order to obtain high efficiency of light excitation and collection, two front lenses with high numerical apertures (N.A. = 0.38) driven by compact nano-positioners are directly integrated on the scanner head without degrading its mechanical and thermal stability. The electric noise floor of the background current is 5 fA/Hz1/2, and the maximum vibrational noise of the tip height is below 200 fm/Hz1/2. The drift of the tip-sample spacing is smaller than 0.1 pm/min. Such a rigid scanner head yields small background noise (oscillation amplitude of ∼2 pm without excitation) and high quality factor (Q factor up to 140 000) for the qPlus sensor. Atomic-resolution imaging and inelastic electron tunneling spectroscopy are obtained under the scanning tunneling microscope mode on the Au(111) surface. The hydrogen-bonding structure of two-dimensional (2D) ice on the Au(111) surface is clearly resolved under the atomic force microscope (AFM) mode with a CO-terminated tip. Finally, the electroluminescence spectrum from a plasmonic AFM tip is demonstrated, which paves the way for future photon-assisted SPM experiments.Laser powder bed fusion (LPBF) is a highly dynamic multi-physics process used for the additive manufacturing (AM) of metal components. Improving process understanding and validating predictive computational models require high-fidelity diagnostics capable of capturing data in challenging environments. Synchrotron x-ray techniques play a vital role in the validation process as they are the only in situ diagnostic capable of imaging sub-surface melt pool dynamics and microstructure evolution during LPBF-AM. In this article, a laboratory scale system designed to mimic LPBF process conditions while operating at a synchrotron facility is described. The system is implemented with process accurate atmospheric conditions, including an air knife for active vapor plume removal. Significantly, the chamber also incorporates a diagnostic sensor suite that monitors emitted optical, acoustic, and electronic signals during laser processing with coincident x-ray imaging. The addition of the sensor suite enables validation of these industrially compatible single point sensors by detecting pore formation and spatter events and directly correlating the events with changes in the detected signal. Experiments in the Ti-6Al-4V alloy performed at the Stanford Synchrotron Radiation Lightsource using the system are detailed with sufficient sampling rates to probe melt pool dynamics. X-ray imaging captures melt pool dynamics at frame rates of 20 kHz with a 2 µm pixel resolution, and the coincident diagnostic sensor data are recorded at 470 kHz. This work shows that the current system enables the in situ detection of defects during the LPBF process and permits direct correlation of diagnostic signatures at the exact time of defect formation.The influence of the light source noise can be reduced by subtracting the signal of the light source noise (reference signal) from that of the probe light (probe signal). Here, it is essential that the intensities of the signals are equated. To equate the intensities, an auto-balancing method is widely employed, where the gain of the probe signal is feedback-controlled, regarding the DC component in the subtraction as an error signal. However, DC-offset drift causes a deviation from the optimal intensity balance. Additionally, the DC component is often several orders of magnitude larger than the sample signal, which requires a high-dynamic range in the circuitry. Furthermore, if the feedback control is too fast, it cancels out the sample signal. In this study, we formulate a noise correlation auto-balancing method, where the correlation of the reference signal and residual noise in the subtraction is employed as the error signal. With this scheme, all the above problems are avoided. The feasibility of the algorithm was demonstrated by a prototype circuitry and signals emulating the probe and reference signals. It did not suffer from the DC-offset drift, while a 44-dB canceling rate with auto-balancing of a 1.3-MHz cutoff frequency was demonstrated. We foresee, such as in pump/probe measurements, that this scheme improves the robustness, dynamic range, and response time required to follow changes in transmittance and the measurement position of the sample while employing a light source that is advantageous in wavelength selectivity, coherence, and cost but is noisy.Deuterium-tritium neutron yield has reached up to about 1013 at the 100 kJ-level laser facility, which makes measurement of neutron emission images possible with the neutron imaging system. There are two methods to collect neutron images from the scintillator array, optical fiber taper and the lens system. Here, we report a design of the lens system for the neutron imaging system at the 100 kJ-level laser facility. The lens system, which consists of a nine-element collecting lens, with a spatial resolution of 20 µm and a light-collection efficiency of 5.9% has been designed.In powder-bed-based metal additive manufacturing (AM), the visualization and analysis of the powder spreading process are critical for understanding the powder spreading dynamics and mechanisms. Unfortunately, the high spreading speeds, the small size of the powder, and the opacity of the materials present a great challenge for directly observing the powder spreading behavior. Here, we report a compact and flexible powder spreading system for in situ characterization of the dynamics of the powders during the spreading process by high-speed x-ray imaging. The system enables the tracing of individual powder movement within the narrow gap between the recoater and the substrate at variable spreading speeds from 17 to 322 mm/s. The instrument and method reported here provide a powerful tool for studying powder spreading physics in AM processes and for investigating the physics of granular material flow behavior in a confined environment.We present a self-locking laser system that does not require operator interventions. The system automatically finds a desired atomic transition and subsequently locks to it. Moreover, it has the ability to automatically detect if the laser is out of lock and activate the re-locking process. The design was implemented on two different diode lasers, a distributed Bragg reflector (DBR) diode laser and a Fabry Perot (FP) diode laser, used as a repump laser for a magneto-optical trap in a laser cooling experiment and a Raman laser for a four-level Raman transition experiment, respectively. The design relies on frequency modulation transfer spectroscopy to obtain a sub-Doppler atomic spectrum of rubidium-85. This spectrum is then demodulated to obtain zero-crossing linear slopes at the exact points of each atomic and crossover transition. The frequency modulation, the signal analysis, and the automatic locking and re-locking of the lasers are all implemented using an Arduino Due microcontroller. The lock loop has a bandwidth of 7 kHz. The lasers used for the design are characterized, and the robustness of the lock is analyzed. The achieved linewidths of DBR and FP lasers are 1.4 and 5.5 MHz, respectively. The frequency drifts of both lasers are a few 100 kHz over a course of days. The capture range of the locking system is up to 4.9 GHz for the DBR laser and 725 MHz for the FP laser. Both lasers performed well under actual experimental conditions.In this paper, a high-power ultra-wideband radiation system, composed of multiply radiation modules, is developed based on the space-synthesis method. The radiation module mainly consists of a transistorized pulser, a 2 × 2 combined antenna array, and a power divider. To improve the out parameters [the amplitude, the pulse repetition frequency (PRF), and the rise time] of the transistorized pulser based on the Marx circuit, the influence of the traveling wave process on the output pulse must be concerned. Based on the theoretical analysis, the printed circuit board circuit parameters and the circuit structure of the pulser are optimized. selleck inhibitor To improve the power synthesis efficiency, the pulse jitter characteristic of the pulser is improved by replacing the conventional base triggering mode with the collector voltage ramp triggering mode for the first-stage avalanche transistor in the pulser. The previous optimized antenna array is utilized in this radiation system, which has a better radiation performance in the prescribed aperture area. In addition, based on the gradient microstrip structure, the power divider integrated with the pulser is designed, which has the advantages of wide bandwidth, low loss, and light weight. Experimental results show that the peak effective potential rEp of the radiation system of 20 radiation modules is 221.8 kV, the maximum PRF could reach 10 kHz, and the half-power radiation angles of its radiation field are about 5° in both the E plane and the H plane. More radiation modules could be integrated into the system to achieve a higher electric field in the future.Laser power stabilization systems with liquid crystal variable retarders have been employed in miniaturized atomic gyroscopes for the merits of low power consumption and easy integration. However, the long-term power drift of the system output with ambient temperature significantly decreases the long-term performance of atomic gyroscopes. Here, we demonstrated a method of dynamic closed-loop control based on the combination of optical power drift and ambient temperature modeling. For a continuous 45 min operation within an ambient temperature variation range of 23.7-25.3 °C, the relative Allan deviation of the output optical power was decreased by one order of magnitude from 2.29 × 10-4 to 3.35 × 10-5 after 100 s averaging time. The long-term stability of the system was significantly improved. In addition, the scheme requires no additional thermal control device, preventing the introduction of extra electromagnetic interference, which is desirable in a miniaturized atomic gyroscope.In this paper, an image-based visual servoing (IBVS) controller with a 6 degree-of-freedom robotic manipulator that tracks moving objects is investigated using the proposed Deep Q-Networks and proportional-integral-derivative (DQN-PID) controller. First, the classical IBVS controller and the problem of feature loss and large steady-state error for tracking moving targets are introduced. Then, a DQN-PID based IBVS method is proposed to solve the problem of feature loss and large steady-state error and improve the servo precision, as the existing methods are hard to use for solve the problems. Specifically, the IBVS method is inherited by our controller to build the tracking model, and a value-based reinforcement learning method is proposed as an adaptive law for dynamically tuning the PID parameters in the discrete space, which can track the moving target and keep the servo feature in the field of the camera. Finally, compared with the different existing methods, the DQN-PID based IBVS method has merits of higher accuracy and more stable tracking, or generalization.