EXPERIMENTAL SIGNATURE OF REGISTRATION NOISE IN PULSED TERAHERTZ SYSTEMS

2006 ◽  
Vol 06 (01) ◽  
pp. L77-L84 ◽  
Author(s):  
NETTA COHEN ◽  
J. W. HANDLEY ◽  
R. D. BOYLE ◽  
SAMUEL L. BRAUNSTEIN ◽  
ELIZABETH BERRY
Keyword(s):  
Imaging System ◽  
Noise Signal ◽  
Johnson Noise ◽  
Pump Probe ◽  
Terahertz Pulsed Imaging ◽  
Narrowband Signal ◽  
Probe Delay ◽  
Physical Limitations ◽  
Comparison Of The Results ◽  
General Signature

This Letter reports results from time domain measurements in a terahertz pulsed imaging system and suggests that a mechanical resetting mechanism in the pump-probe delay stage results in a small but resolvable noise signal. In the setup described here, this effect dominates all other sources of noise such as the background Johnson noise or shot noise, and can hence be isolated and analysed in detail. An analysis of the noise signal is used to estimate the physical limitations of the pump-probe system being employed. A comparison of the results with an analytic prediction allows us to formulate a useful and general signature of registration noise, that should make it easy to detect in any sufficiently narrowband signal.

scholarly journals Pump-Probe Delay Controlled by Laser-dressed Ionization with Isolated Attosecond Pulses

2021 ◽  
Vol 255 ◽  
pp. 13004
Author(s):  
Martin Luttmann ◽  
David Bresteau ◽  
Thierry Ruchon
Keyword(s):  
Pulse Train ◽  
Femtosecond Pulse ◽  
Photoelectron Spectrum ◽  
Large Range ◽  
Extreme Ultraviolet ◽  
Pump Probe ◽  
Gas Target ◽  
Probe Delay ◽  
Attosecond Pulses ◽  
The Mean

In a recent work [1], we demonstrated how laser-dressed ionization can be harnessed to control with attosecond accuracy the time delay between an extreme-ultraviolet (XUV) attosecond pulse train and an infrared (IR) femtosecond pulse. In this case, the comb-like photoelectron spectrum obtained by ionizing a gas target with the two superimposed beams exhibits peaks oscillating with the delay. Two of them can be found to oscillate in phase quadrature, allowing an optimal measurement and stabilization of the delay over a large range. Here we expand this technique to isolated attosecond pulses, by taking advantage of the delay-modulation of attosecond streaking traces. Although the photoelectron spectrum contains no peaks in that case, it is possible to reconstruct the pump-probe delay by simply monitoring the mean energy of the spectrum and the amplitude at this energy. In general, we find that active delay stabilization based on laser-dressed ionization is possible as long as the XUV pulses are chirped.

Fundamental Comparison of Image Quality Metrics

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 81-81
Author(s):  
P G J Barten
Keyword(s):  
Image Quality ◽  
Spatial Frequency ◽  
Imaging System ◽  
Quality Metrics ◽  
Sensitivity Function ◽  
Just Noticeable Difference ◽  
Modulation Transfer ◽  
Image Quality Metrics ◽  
Comparison Of The Results ◽  
The Right

In most image quality metrics (eg MTFA, ICS, SQF, DDD, SQRI) use is made of the modulation transfer function (MTF) of the imaging system and the contrast sensitivity function (CSF) of the human visual system. All metrics usually show a positive correlation with perceived image quality. This does not, however, say much about the correctness of the underlying equations. Defocusing experiments where an image is defocused by one just-noticeable difference can give information about the contribution of different spatial-frequency ranges to image quality. By performing defocusing experiments with images where contrast is also varied, information can be obtained about the dependence of image quality on contrast. In our investigation defocusing measurements from Baldwin (1940), Carlson and Cohen (1980) and Watt and Morgan (1983) were used. Comparison of the results with the fundamental dependence of some image quality metrics on spatial frequency and contrast indicates that only the SQRI (square-root integral) showed the right behaviour with respect to these parameters.

scholarly journals Analysis of a measurement scheme for ultrafast hole dynamics by few femtosecond resolution X-ray pump–probe Auger spectroscopy

2014 ◽  
Vol 171 ◽  
pp. 93-111 ◽  
Author(s):  
Bridgette Cooper ◽  
Přemysl Kolorenč ◽  
Leszek J. Frasinski ◽  
Vitali Averbukh ◽  
Jon P. Marangos
Keyword(s):  
Auger Spectroscopy ◽  
X Rays ◽  
Core Hole ◽  
Pump Probe ◽  
X Ray ◽  
Molecular Systems ◽  
The Core ◽  
Probe Delay ◽  
Valence Region ◽  
Hole Migration

Ultrafast hole dynamics created in molecular systems as a result of sudden ionisation is the focus of much attention in the field of attosecond science. Using the molecule glycine we show through ab initio simulations that the dynamics of a hole, arising from ionisation in the inner valence region, evolves with a timescale appropriate to be measured using X-ray pulses from the current generation of SASE free electron lasers. The examined pump–probe scheme uses X-rays with photon energy below the K edge of carbon (275–280 eV) that will ionise from the inner valence region. A second probe X-ray at the same energy can excite an electron from the core to fill the vacancy in the inner-valence region. The dynamics of the inner valence hole can be tracked by measuring the Auger electrons produced by the subsequent refilling of the core hole as a function of pump–probe delay. We consider the feasibility of the experiment and include numerical simulation to support this analysis. We discuss the potential for all X-ray pump-X-ray probe Auger spectroscopy measurements for tracking hole migration.

scholarly journals In-situ diagnostic of femtosecond laser probe pulses for high resolution ultrafast imaging

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Chen Xie ◽  
Remi Meyer ◽  
Luc Froehly ◽  
Remo Giust ◽  
Francois Courvoisier
Keyword(s):  
Spatial Frequency ◽  
Probe Pulse ◽  
Imaging Techniques ◽  
Frame Rate ◽  
Pulse Front ◽  
Pump Probe ◽  
Ultrafast Imaging ◽  
Probe Delay

AbstractUltrafast imaging is essential in physics and chemistry to investigate the femtosecond dynamics of nonuniform samples or of phenomena with strong spatial variations. It relies on observing the phenomena induced by an ultrashort laser pump pulse using an ultrashort probe pulse at a later time. Recent years have seen the emergence of very successful ultrafast imaging techniques of single non-reproducible events with extremely high frame rate, based on wavelength or spatial frequency encoding. However, further progress in ultrafast imaging towards high spatial resolution is hampered by the lack of characterization of weak probe beams. For pump–probe experiments realized within solids or liquids, because of the difference in group velocities between pump and probe, the determination of the absolute pump–probe delay depends on the sample position. In addition, pulse-front tilt is a widespread issue, unacceptable for ultrafast imaging, but which is conventionally very difficult to evaluate for the low-intensity probe pulses. Here we show that a pump-induced micro-grating generated from the electronic Kerr effect provides a detailed in-situ characterization of a weak probe pulse. It allows solving the two issues of absolute pump–probe delay determination and pulse-front tilt detection. Our approach is valid whatever the transparent medium with non-negligible Kerr index, whatever the probe pulse polarization and wavelength. Because it is nondestructive and fast to perform, this in-situ probe diagnostic can be repeated to calibrate experimental conditions, particularly in the case where complex wavelength, spatial frequency or polarization encoding is used. We anticipate that this technique will enable previously inaccessible spatiotemporal imaging in a number of fields of ultrafast science at the micro- and nanoscale.

Research on Acoustic Source Localization Technology Based on Cross-Correlation

2013 ◽  
Vol 819 ◽  
pp. 244-248
Author(s):  
Zhi Jiang Xie ◽  
Hai Zeng ◽  
Ping Chen
Keyword(s):  
Source Localization ◽  
Cross Correlation ◽  
Microphone Array ◽  
Noise Signal ◽  
Acoustic Source ◽  
Localization Accuracy ◽  
Correlation Algorithm ◽  
Acoustic Source Localization ◽  
Narrowband Signal ◽  
Improved Accuracy

In order to realize acoustic source localization, we proposed to use microphone array and time delay based on crosscorrelation algorithm,and analyzed the factors to influence the locating accuracy, and established a realtime acoustic source localizationsystem on the NI CompactRIO system. By experiments, cross-correlation algorithm for wideband signal(sweep signal, noise signal) localization is more accurate, for narrowband signal (organ signal) localization is less significant. After analyzed factors to influence the localization accuracy, we improved sound source system, and the factors that affected the organ signal localization is verified by experiment , and improved accuracy of narrowband signal localization .

scholarly journals Negative photoconductance in 150 GHz transients from irradiated p-type Cz-Silicon

2021 ◽  
Author(s):  
Biswadev Roy ◽  
Marvin Wu
Keyword(s):  
Laser Fluence ◽  
Time Resolved ◽  
Pump Probe ◽  
Boron Doped ◽  
Probe Delay ◽  
Probe Voltage ◽  
Probe Spectroscopy ◽  
P Type ◽  
Chlorine Ion ◽  
Beam Damage

Boron doped (p-type) silicon wafers of the same type are irradiated with gamma, proton and chlorine ion beams. This causes radiation damage in the form of migration of vacancies, traps to photoelectrons. We use time-resolved millimeter wave pump-probe spectroscopy (150 GHz CW probe signal) and 532 nm ultrafast laser as pump source with variable fluence. Upon studying the transient response of the detector probe voltage as function of the pump-probe delay period we note a good positive (absorption) photoconductance peak and soon after recombination of photocarriers there occurs a negative photoconductance (NPC) transient. We consistently find that the NPC lasts for about 36 microseconds and this study points out that the positive to NPC peaks for each laser fluence varies with the type of radiation damaged samples.2 MeV proton beam damage create damage that trap carriers very effectively, and enhances the resistivity of the silicon wafer from 15 Ohms to 150 Ohms. The Chlorine ion damaged silicon responds consistently to the 150 GHz probe beam and correlates strongly with the laser fluence.

scholarly journals Remote Hyperspectral Imaging Acquisition and Characterization for Marine Litter Detection

2021 ◽  
Vol 13 (13) ◽  
pp. 2536
Author(s):  
Sara Freitas ◽  
Hugo Silva ◽  
Eduardo Silva
Keyword(s):  
Hyperspectral Imaging ◽  
Hyperspectral Image ◽  
Imaging System ◽  
Spectral Response ◽  
Ground Truth ◽  
Supervised Machine Learning ◽  
Support Vector ◽  
Observation Data ◽  
Marine Litter ◽  
Comparison Of The Results

This paper addresses the development of a remote hyperspectral imaging system for detection and characterization of marine litter concentrations in an oceanic environment. The work performed in this paper is the following: (i) an in-situ characterization was conducted in an outdoor laboratory environment with the hyperspectral imaging system to obtain the spatial and spectral response of a batch of marine litter samples; (ii) a real dataset hyperspectral image acquisition was performed using manned and unmanned aerial platforms, of artificial targets composed of the material analyzed in the laboratory; (iii) comparison of the results (spatial and spectral response) obtained in laboratory conditions with the remote observation data acquired during the dataset flights; (iv) implementation of two different supervised machine learning methods, namely Random Forest (RF) and Support Vector Machines (SVM), for marine litter artificial target detection based on previous training. Obtained results show a marine litter automated detection capability with a 70–80% precision rate of detection in all three targets, compared to ground-truth pixels, as well as recall rates over 50%.

Time-resolved coherent Raman spectroscopy by high-speed pump-probe delay scanning

2014 ◽  
Vol 39 (14) ◽  
pp. 4124 ◽  
Author(s):  
S. R. Domingue ◽  
D. G. Winters ◽  
R. A. Bartels
Keyword(s):  
Raman Spectroscopy ◽  
High Speed ◽  
Time Resolved ◽  
Pump Probe ◽  
Probe Delay ◽  
Coherent Raman

scholarly journals Negative photoconductance in 150 GHz transients from irradiated p-type Cz-Silicon

2021 ◽  
Author(s):  
Biswadev Roy ◽  
Marvin Wu
Keyword(s):  
Laser Fluence ◽  
Time Resolved ◽  
Pump Probe ◽  
Boron Doped ◽  
Probe Delay ◽  
Probe Voltage ◽  
Probe Spectroscopy ◽  
P Type ◽  
Chlorine Ion ◽  
Beam Damage

Boron doped (p-type) silicon wafers of the same type are irradiated with gamma, proton and chlorine ion beams. This causes radiation damage in the form of migration of vacancies, traps to photoelectrons. We use time-resolved millimeter wave pump-probe spectroscopy (150 GHz CW probe signal) and 532 nm ultrafast laser as pump source with variable fluence. Upon studying the transient response of the detector probe voltage as function of the pump-probe delay period we note a good positive (absorption) photoconductance peak and soon after recombination of photocarriers there occurs a negative photoconductance (NPC) transient. We consistently find that the NPC lasts for about 36 microseconds and this study points out that the positive to NPC peaks for each laser fluence varies with the type of radiation damaged samples.2 MeV proton beam damage create damage that trap carriers very effectively, and enhances the resistivity of the silicon wafer from 15 Ohms to 150 Ohms. The Chlorine ion damaged silicon responds consistently to the 150 GHz probe beam and correlates strongly with the laser fluence.

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