Displacement measurement is a fundamental functionality in modern science and technology. Although there has been remarkable progress in the precision of such measurements with various laser ranging ...methods1–8, they are incapable of capturing fast and complex mechanical displacements. Here, we have established a displacement measurement method using time-of-flight detection9 with femtosecond optical pulses and frequency-locked electrical waveforms. This method uniquely combines ultrafast measurement speed, sub-nanometre precision and non-ambiguity range of more than several millimetres. The achieved performance features unprecedented detection speed and precision. Starting from 24 nm precision for 4 ns acquisition time, the precision can reach 180 pm for 5 ms acquisition time. Using this method, we show real-time detection of single-event, fast and high-dynamic-range mechanical displacements. This capability can lead to the realization of new measurement and analysis platforms for studying broadband, transient and nonlinear mechanical dynamics in real time, which will be useful for directly probing optomechanics10, the onset of cracks11, dynamic deformations12, nonlinear vibrations13, ultrasonic phenomena14 and cell-generated forces15.Using a femtosecond mode-locked laser and a frequency-locked electric signal, a displacement measurement method that offers a >MHz measurement speed, sub-nanometre precision and a measurement range of more than several millimetres is achieved, facilitating the study of broadband, transient and nonlinear mechanical dynamics in real time.
Distribution of a high-stability clock signal is an important topic for many applications. Recently, optical frequency comb transfer through outdoor atmosphere has become a valuable tool for the ...clock distribution due to its versatility. To extend the benefits of comb-based open-air clock distribution, one-way radiofrequency (RF) transfer with a single optical frequency comb is an attractive approach due to its simplicity and broad application span. Here, we transfer an L-band RF signal across 820-m-scale outdoor beam path with a single optical frequency comb. We measured the absolute phase noise of the transferred RF signal, and analyzed it with Kolmogorov’s
f
−8/3
power law and Taylor’s hypothesis of frozen turbulence. We also show that the residual-phase noise of the transferred RF signal can be suppressed to the femtosecond regime by a delay-locked loop. Our results may benefit remote ranging at km-range, inter-building clock distribution, and optical communication through aerial drones.
Stroboscopic visualization of nuclear or electron dynamics in atoms, molecules or solids requires ultrafast pump and probe pulses and a close to perfect synchronization between the two. We have ...developed a 3 MeV ultrafast electron diffraction (UED) probe technology that nominally reduces the electron bunch duration and the arrival time jitter to the subfemtosecond level. This simple configuration uses a radiofrequency photogun and a 90° achromatic bend and is designed to provide effectively jitter-free conditions. Terahertz streaking measurements reveal an electron bunch duration of 25 fs, even for a charge as high as 0.6 pC, and an arrival time jitter of 7.8 fs, the latter limited by only the measurement accuracy. From pump–probe measurements of photoexcited bismuth films, the instrument response function was determined to be 31 fs. This pioneering jitter-free technique paves the way towards UED of attosecond phenomena in atomic, molecular and solid-state dynamics.An ultrafast electron diffraction facility with an overall temporal resolution of 31 fs root mean square is developed. Even for a charge as high as 0.6 pC, the electron bunch duration and timing jitter are 25 fs and less than 10 fs, respectively.
The demand for high-resolution and large-area imaging systems for non-destructive wafer inspection has grown owing to the increasing complexity and extremely fine nature of semiconductor processes. ...Several studies have focused on developing high-resolution imaging systems; however, they were limited by the tradeoff between image resolution and field of view. Hence, computational imaging has arisen as an alternative method to conventional optical imaging, aimed at enhancing the aforementioned parameters. This study proposes a method for improving the resolution and field of view of an image in a lens-less reflection-type system. Our method was verified by computationally restoring the final image from diffraction images measured at various illumination positions using a visible light source. We introduced speckle illumination to expand the numerical aperture of the entire system, simultaneously improving image resolution and field of view. The image reconstruction process was accelerated by employing a convolutional neural network. Using the reconstructed phase images, we implemented high-resolution topography and demonstrated its applicability in wafer surface inspection. Furthermore, we demonstrated an ideal diffraction-limited spatial resolution of 1.7 μm over a field of view of 1.8 × 1.8 mm
for the topographic imaging of targets with various surface roughness. The proposed approach is suitable for applications that simultaneously require high throughput and resolution, such as wafer-wide integrated metrology, owing to its compact design, cost-effectiveness, and mechanical robustness.
The increase in <inline-formula> <tex-math notation="LaTeX">{R} _{DUT} </tex-math></inline-formula>, the on-state resistance of power semiconductor devices, is used to estimate the remaining useful ...life (RUL) of the devices. Conventional online measurement of <inline-formula> <tex-math notation="LaTeX">R_{DUT} </tex-math></inline-formula> involves on-state voltage measurement of the on-state device, which is easily polluted by switching noise to limit the measurement accuracy. This paper proposes a new noise-robust method to measure the increment of <inline-formula> <tex-math notation="LaTeX">R_{DUT} </tex-math></inline-formula> by inductor current and input/output DC voltage of DC-DC converters. The proposed method features higher accuracy in predicting RUL than the conventional one because the inductor current is immune to switching noise. The aging of MOSFET is emulated in this paper by adding a series resistor <inline-formula> <tex-math notation="LaTeX">R_{ext} </tex-math></inline-formula>. Experiments showed that the resistance increment measured by the proposed method is up to 99.2% accurate to value of <inline-formula> <tex-math notation="LaTeX">R_{ext} </tex-math></inline-formula>.
Abstract
The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen ...visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed “single-shot oscilloscope” will open up new avenue for developing the real-time petahertz (PHz) metrology.
Timing jitter is one of the most important properties of femtosecond mode-locked lasers and optical frequency combs. Accurate measurement of timing jitter power spectral density (PSD) is a critical ...prerequisite for optimizing overall noise performance and further advancing comb applications both in the time and frequency domains. Commonly used jitter measurement methods require a reference mode-locked laser with timing jitter similar to or lower than that of the laser-under-test, which is a demanding requirement for many laser laboratories, and/or have limited measurement resolution. Here we show a high-resolution and reference-source-free measurement method of timing jitter spectra of optical frequency combs using an optical fibre delay line and optical carrier interference. The demonstrated method works well for both mode-locked oscillators and supercontinua, with 2 × 10
fs
/Hz (equivalent to -174 dBc/Hz at 10-GHz carrier frequency) measurement noise floor. The demonstrated method can serve as a simple and powerful characterization tool for timing jitter PSDs of various comb sources including mode-locked oscillators, supercontinua and recently emerging Kerr-frequency combs; the jitter measurement results enabled by our method will provide new insights for understanding and optimizing timing noise in such comb sources.
Criteria Based Content Analysis (CBCA) is a forensic tool that analyzes victim statements. It involves the categorization of victims' statements into 19 distinct criteria classifications, playing a ...crucial role in evaluating the authenticity of testimonies by discerning whether they are rooted in genuine experiences or fabricated accounts. The exclusion of subjective opinions becomes imperative to assess statements through this forensic tool objectively. This study proposes developing an objective classification model for CBCA-based statement analysis using natural language processing techniques. Nevertheless, achieving optimal classification performance proves challenging due to imbalances in data distribution among the various criterion classifications. To enhance the accuracy and reliability of the classification model, this research employs data augmentation techniques and dual contrastive learning methods for fine-tuning the RoBERTa language model. Furthermore, model-based optimization techniques are also applied to identify augmented hyper-parameters and maximize the model's classification performance. The study's findings, including an 8.5% improvement in macro F1 score compared to human classification results, a 24% improvement in macro F1 score, and a 13% improvement in accuracy compared to previous human classification results, suggest that the proposed model is highly effective in reducing the influence of human subjectivity in statement analysis. The proposed model has significant implications for legal proceedings and criminal investigations, as it can provide a more objective and reliable method for evaluating the credibility of victim statements. Reducing human subjectivity in the statement analysis process can increase the accuracy of verdicts and help ensure that justice is served.
In cases of child sexual abuse, interviewing and obtaining trustworthy statements from victims and witnesses is essential because their statements are the only evidence. It is crucial to ascertain ...objectively the credibility of the victim’s statements, which may vary based on the nature of the questions posed by the forensic interviewer. Therefore, interview skills that eliminate subjective opinions require a high level of training for forensic interviewers. To reduce high-risk subjective interviews, objectively analyzing statements is essential. Understanding the victim’s intent and named entity recognition (NER) in the statements is necessary to give the victim open-ended questions and memory recall. Therefore, the system provides an intent classification and NER method that follows the National Institute of Child Health and Human Development Investigative Interview Protocol, which outlines the collection of objective statements. Large language models such as BERT and KoBERT, along with data augmentation techniques, were proposed using a restricted training dataset of limited size to achieve effective intent classification and NER performance. Additionally, a system that can collect objective statements with the proposed model was developed and it was confirmed that it could assist statement analysts. The verification results showed that the model achieved average F1-scores of 95.5% and 97.8% for intent classification and NER, respectively, which improved the results of the limited data by 3.4% and 3.7%, respectively.
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