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- 摘要
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- 实验方案
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Dechirping Compression Method for Nonlinear Frequency Modulation Waveforms
摘要： This letter proposes a novel dechirp processing method for wideband nonlinear frequency modulation (NLFM) waveform which enables low sampling rate of data. As we know, NLFM waveform can easily realize optimal shape of power spectral density which helps to achieve better pulse compression result with low range sidelobes without signal-to-noise ratio degradation caused by weighting as we usually do for LFM waveforms. In the approach, hamming window is adopted in the generation of the NLFM waveform for better balance on the low range sidelobes and a relative small bandwidth. In dechirp operation, the NLFM radar echoes are mixed with a local reference LFM signal, and thus narrowband signals are resulted and only low sampling rate is needed. The dechirped NLFM signals are then up-sampled and inverse dechirped by software and ?nally matched ?ltering is conducted to complete pulse compression. Both numerically simulated data and real radar data are processed to verify the effectiveness of the proposed method.
关键词： nonlinear frequency modulation (NLFM),sampling rate,pulse compression,Dechirp processing
更新于2025-09-23 15:23:52
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Compression of femtosecond pulses in a wide wavelength range using a large-mode-area tapered fiber
摘要： We report the design of a tapered fiber that can be used for the compression of pulses at different central wavelengths. The proposed fiber is a three-layer W-type large-mode-area fiber, which has been tapered to transform the mode area from 1700 μm2 to 900 μm2. We determine the exact length of the maximum pulse compression and numerically demonstrate the compression of a 250 fs, 100 kW peak power input pulse to 15 fs, 850 kW at 1.55 μm wavelength and compression of 250 fs, 120 kW peak power input pulses to 28 fs, 700 kW and to 46 fs, 500 kW at 1.8 μm and 2 μm wavelengths, respectively. Such a fiber can find wide ranging applications, including in communication, spectroscopy and medicine.
关键词： ultrafast processes in fiber,large-mode-area fiber,high peak power femtosecond pulses,pulse shaping,tapered fiber,pulse compression
更新于2025-09-23 15:22:29
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Sparse Reconstruction-Based Thermal Imaging for Defect Detection
摘要： This paper proposes an idea of employing sparse reconstruction-based technique for thermal imaging defect detection. The implementation of the reconstruction technique is tested on a carbon fiber reinforced polymer test piece with artificially drilled defects and the test results are compared with the established cross correlation method. The two processes are compared in terms of defect detectability, their SNR variation with defect depth and their computation complexity. When compared with cross correlation algorithm, the technique is expected to solve memory space problems by compressing all information from large cross-correlated pulse video into a single reconstructed image as an output. Furthermore, in existing cross correlation methods, the pulse peak time shifts with defect depth. Hence, defect quantification algorithms, such as SNR calculation, require multiple frame analysis. Such algorithms are comparatively simplified in sparse reconstruction technique. This paper explores sparse reconstruction algorithm for resolving close-spaced defects. This paper further describes cross-validation method for optimization of a user parameter in sparse reconstruction method.
关键词： thermal nondestructive testing,sparse reconstruction,pulse compression,nondestructive evaluation and remote sensing,frequency modulated thermal wave imaging,Cross correlation algorithm
更新于2025-09-23 15:22:29
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SBS pulse compression using bulk fused silica by diode-pumped solid-state lasers at 1??kHz repetition rate
摘要： This study is focused on constructing a highly stable diode-pumped solid-state laser system by conducting experiments on high-repetition-rate SBS pulse compression using bulk fused silica. A multi-rod serial-connection structure is adopted for SBS expriments by comparing K8 glass and fused silica medium at a 10 Hz repetition rate. The optimized structure is obtained according to variation of the pump power density. Based on the optimized structure, fused silica-based SBS pulse compression is carried out in the range of 100–1000 Hz and the parameter performance of laser system after compression is also evaluated by comparing a HT270 liquid medium. Experimental results indicate that the energy e?ciency of fused silica-based SBS is improved by approximately 40% compared with that of K8 glass. Further, the energy relative standard deviation of fused silica-based SBS is reduced by approximately 88% compared with HT270 medium, indicating that bulk fused silica is advantageous for high-repetition-rate SBS pulse compression because of its un-?uidity, high thermal conductivity and power-load ability. In addition, a 1 kHz highly-stable sub-nanosecond compressed pulse is achieved using bulk fused silica medium at a pump energy of 50 mJ. Furthermore, the SBS energy e?ciency can be further improved by increasing the input energy.
关键词： Pulse compression,High repetition rate,Solid-state lasers,Sub-nanosecond pulse,Stimulated Brillouin scattering (SBS)
更新于2025-09-23 15:21:01
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Ytterbium laser system for studying parametric amplification of femtosecond pulses with a centre wavelength of a??2 ??m
摘要： A laser system is developed with an optical synchronisation of a femtosecond signal with a pump channel. The signal of a driving ytterbium fibre laser with a 60 MHz repetition rate of stretched femtosecond pulses is amplified in energy from several nanojoules to 0.4 mJ at a pulse repetition rate of 3 kHz in a wide-band amplifier and then is compressed in time to 250 fs. The obtained radiation is used for generating femtosecond laser pulses with a centre wavelength of ~2 mm, pulse energy of above 20 mJ, duration of several field oscillations, and phase stabilisation between the electromagnetic field and envelope. The other pulse of the driving fibre laser provides optical synchronisation and a minimal time delay and is directed to a regenerative Yb : YAG disk amplifier for amplification to an energy of 4 mJ at a pulse repetition rate of 3 kHz and duration of 20 ps. A multipass disk amplifier is developed for further increasing the energy of pump chirped pulses to an energy of 70 mJ at a pulse repetition rate of 10 Hz and duration of 400 ps for studying parametric amplification under sub-nanosecond pumping.
关键词： parametric amplification,Yb :YAG disk amplifier,ytterbium fibre laser,femtosecond pulses,pulse compression
更新于2025-09-23 15:19:57
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Threshold decrease and output-power improvement in dual-loss Q-switched laser based on few-layer WTe<sub>2</sub> saturable absorber
摘要： A dual-loss Q-switched laser was realized by applying a home-made 2.5 nm-thick WTe2 to an acoustic-optic (AO) modulated laser. Besides conventional pulse compression, the participation of WTe2 could obviously improve the average output power by 29.6% and reduce the laser threshold by 20%, even with the introduced 8% nonsaturable loss. The average-output-power improvement and pulse compression in this dual-loss modulated laser resulted in a 113.7% increase of peak power. According to the measured spectra of laser and photoluminescence of WTe2, the laser-induced excitonic light-emission may be the reason of this laser gain.
关键词： WTe2 saturable absorber,laser threshold decrease,pulse compression,output-power improvement,dual-loss Q-switched laser
更新于2025-09-23 15:19:57
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[IEEE 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Singapore (2018.7.16-2018.7.19)] 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - High Sensitivity Ultrasonic Inspection Technique Using Pulse Compression Method
摘要： We developed an ultrasonic inspection technique using a pulse compression method for detecting bonding defects with interfaces of stacked wafers. This technique can detect the minute echoes reflected from the bonding interfaces by computing the correlation function between transmitted and received signals. We designed a measurement condition for pulse compression with a transmitted signal and took an ultrasonic measurement of a 3-layer stacked sample. We compared the defect detection sensitivity of the pulse compression method with the ultrasonic inspection using pulse waves. The experimental results showed that the noise of an ultrasonic image was reduced and minute defects could be detected by applying developed method.
关键词： multi-layer staked sample,Correlation function,Defect detection,Ultrasonic inspection,Pulse compression
更新于2025-09-19 17:15:36
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Nonlinear compression of high-power laser pulses: compression after compressor approach
摘要： The peak power of present-day lasers is limited by the pulse energy that the diffraction gratings of an optical compressor can withstand. A promising method to overcome this limitation is reviewed: the pulse power is increased by shortening its duration rather than increasing the pulse energy, the pulse being shortened after passing a compressor (Compression after Compressor Approach (CafCA)). For this purpose, the pulse spectrum is broadened as a result of self-phase modulation, and the pulse is then compressed by dispersion mirrors. Application of this idea, known since the 1960s, to lasers whose power is over 1 TW has been restrained until recently by a number of physical problems. These problems and possible methods to solve them are discussed in detail. The experimental results obtained over the past few years demonstrate the efficiency of the technique (compression by a factor of 5) in the range up to 250 TW. CafCA features three undisputed merits: simplicity and low cost, negligible loss of pulse energy, and applicability to any high-power laser.
关键词： nonlinear laser pulse compression,ultrahigh power femtosecond lasers,phase self-modulation,small-scale self-focusing
更新于2025-09-19 17:13:59
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[IEEE 2019 Workshop on Recent Advances in Photonics (WRAP) - Guwahati, India (2019.12.13-2019.12.14)] 2019 Workshop on Recent Advances in Photonics (WRAP) - Picosecond Fundamental Soliton Pulse Compression in Self-similarly designed Chalcogenide Taper Photonic Crystal Fiber
摘要： We numerically demonstrate a pulse compression scheme to compress picosecond fundamental soliton at 2500 nm using Self-similarly designed chalcogenide tapered photonic crystal fiber. Exponentially decreasing dispersion along the length of the fiber act as a tool for the compression process. Dynamics of propagating fundamental soliton has been studied by utilizing nonlinear Schr?dinger equation. Quality analysis has also been investigated for different fiber length to achieve efficient compression condition to achieve high quality IR regime pulses.
关键词： Photonic crystal fiber,Chalcogenide fiber,Supercontinuum generation,Pulse Compression,self-similar Analysis
更新于2025-09-19 17:13:59
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Influences of nanosecond pulse pre-irradiation on femtosecond laser damage resistance of gold pulse compression grating
摘要： The gold pulse compression gratings (PCG) used in the Bidirectional Grating Compressor (BGC) suffers a nano- and femtosecond dual pulses irradiation. In the case that the ns pre-pulse comes 10 nanoseconds early before the fs pulse, experiments were conducted to investigate damage behaviors under the dual pulse irradiation. 1-on-1 laser induced damage threshold (LIDT) of the ns–fs dual pulses and fs single pulse were tested and compared. Scanning Electron Microscope (SEM) was employed to capture damage onset and exam the damage macro- and micro-morphologies. The mono-shot method, comparison between the damage zone and spatial distribution of laser pulses, was employed to analyze the difference of the damage onset fluences for the two cases thoroughly. It was found that there is no degradation of laser damage resistance due to the ns pre-pulse. Instead, a slightly increase (～10%) of fs LIDT caused by the ns pre-pulse was found.
关键词： Femtosecond laser damage,Nano- and femtosecond dual beam processing,Nanosecond pre-pulse,Gold-coated pulse compression gratings,Bidirectional grating compressor
更新于2025-09-16 10:30:52