- 标题
- 摘要
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- 实验方案
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The effect of target thickness on the efficiency of high-order harmonics generated from laser-driven overdense plasma target
摘要： In this paper, we analytically and numerically studied the impact of the target thickness on the efficiency of laser-plasma based high-order harmonics generation (HHG). The optimal parametric region is acquired where the laser normalized amplitude a0, the target density ne and thickness d0 satisfy the relation: a0nc/ne < d0 < a0nc/2ne. In this region, the laser can partially penetrate the target, leading to efficient acceleration of the target. Meanwhile, the target is thick enough to oscillate along the rising edge of the laser without being broken, which guarantees the occurrence of HHG. Both one-dimensional and two-dimensional particle-in-cell simulation results verify our optimal target thickness theory, and a single attosecond pulse with I = 3.0 × 1020 W cm?2 is generated under the driving of 8.6 × 1020 W cm?2, which is several hundred times more intense than that from a thick target.
关键词： the Doppler effect,conversion efficiency,high-order harmonics,intense laser
更新于2025-09-23 15:19:57
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[IEEE 2018 28th International Telecommunication Networks and Applications Conference (ITNAC) - Sydney, Australia (2018.11.21-2018.11.23)] 2018 28th International Telecommunication Networks and Applications Conference (ITNAC) - Wi-Fi Based Device-free Microwave Ghost Imaging Indoor Surveillance System
摘要： In this paper, we propose an Wi-Fi based device-free microwave ghost imaging (GI) indoor surveillance system. Wireless-Fidelity (Wi-Fi) signals originally designed for communication purposes are employed as the incoherent illumination source in the framework of microwave GI. The object reconstruction procedure of microwave GI is modified to fit indoor scenarios where both stationary and moving objects are presented. Numerical simulation validates that the proposed Wi-Fi based microwave GI scheme can effectively isolate indoor targets reflections with different velocities and obtain focused images respectively. Since the proposed system takes the advantage of existing Wi-Fi access points (APs) as its transceivers, it can be regarded as a device-free system and its complexity and operational cost have been significantly reduced.
关键词： device-free,microwave ghost imaging,Wi-Fi,Doppler effect
更新于2025-09-19 17:15:36
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Influence of the Doppler Effect on the Carrier-Envelope Phase
摘要： Carrier-envelope phase (CEP) stabilization plays an important role in the field of attosecond pulse generation and high-field physics [1]. Low-jitter CEP stabilization of ultrashort pulses typically relies on active stabilization schemes, either employing feedback or feed-forward control. However, both established methods come with a detrimental side effect. Feedback control directly modulates pump power or intracavity loss, which causes unwanted power fluctuations of the laser output. While feed-forward control does not corrupt the output stability, it nevertheless induces beam pointing variations in the acousto-optic frequency shifter employed. Here we demonstrate a novel method for modulating the CEP of a laser oscillator, which is based on the Doppler effect and displays neither of the above-mentioned side-effects.
关键词： Doppler effect,CEP stabilization,ultrashort pulses,carrier-envelope phase,laser oscillator
更新于2025-09-16 10:30:52
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[Laser Institute of America ICALEO? 2016: 35th International Congress on Applications of Lasers & Electro-Optics - San Diego, California, USA (October 16–20, 2016)] International Congress on Applications of Lasers & Electro-Optics - Velocity and range measurement optical frequency stepped chirp modulated coherent LIDAR for space application
摘要： The spacecraft landing on Mars or other planets generally requires measuring relative velocity and distance between itself and the land. The measurement demands high accuracy and high reliability. This paper presents an optical frequency stepped chirp modulated pulse train coherent lidar technology for range and velocity measurement. This paper advances an all-fiber structure lidar. It has advantages of small size, high efficiency, low power consumption and stable performance. This paper introduces the optical frequency stepped chirp modulation technology. It gives the semiconductor seed laser theoretical model of driver current versus laser frequency, and computes the modulation waveform. We use an AWG (arbitrary waveform generator) to load the waveform and get the optical stepped chirp modulated pulse train. This paper derives the ambiguous function of the lidar. This function provides a powerful tool to analyze the property and find the highlight property of this lidar: high effective time-bandwidth products. The property gives high range accuracy and velocity accuracy. The signal processing method is advanced. The algorithm can get the range and velocity simultaneously. The Doppler effect caused by target motion is analyzed. The rang walk error caused by Doppler effect is compensated by special algorithm.
关键词： Optical coherence,detection,frequency modulation,lidar,Doppler effect,fiber laser
更新于2025-09-16 10:30:52
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Fiber Optic and Atmospheric Optical Communication || Fading in Optical Communication Channels
摘要： As was mentioned in [1, 2], in most optical wired and wireless systems operated in the atmosphere [3, 4], there occur multiple diffraction, multiple reflection, and multiple scattering effects, due to artificial features inside fibers and dispersion of the inner material, or due to natural obstructions (aerosols, hydrometeors, such as rain, snow and clouds, etc.) filled in the atmosphere. All these effects, which cause not only addition losses (with respect to those obtained in line-of-sight [LOS] above-the-terrain conditions) but also addition fading of the signal strength observed at the detector, can be separated into two independent effects, the slow and the fast fading [5–10]. In real situations occurring in the atmospheric communication links, the various optical signals arriving at the moving or stationary detector via their respective paths have individual phases, which change continuously and randomly. Therefore, both the resultant signal envelope and its phase will also be random variables. Moreover, the Doppler effect can also be explained by random frequency modulation [11–14] due to different Doppler shifts of each of the received signals as multi-ray components. Therefore, to describe slow and fast signal fading, we need to introduce the corresponding mathematical description of the statistical effects that accompany real signal fading in multipath communication channels.
关键词： statistical description,optical communication,Doppler effect,multipath,fading
更新于2025-09-12 10:27:22
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The Analysis of Starlight (Two Centuries of Astronomical Spectroscopy) || The Doppler effect
摘要： An important chapter in the history of astronomical spectroscopy opened on 25 May 1842. On this day Christian Doppler (1803–53) (Fig. 6.1), the professor of mathematics at the University of Prague (then part of Austria), delivered a lecture to the Royal Bohemian Scientific Society entitled ‘Concerning the coloured light of double stars and of some other heavenly bodies’ [1]. By analogy both with sound and waves in the sea, Doppler maintained that light waves undergo a change in frequency of oscillation, and hence of colour, either when the luminous source or the observer is in motion relative to the aether (whose existence was at that time supposed necessary for the transport of light waves). He gave formulae for the frequency change (cid:5)ν when either the source or observer were in motion, and these amounted to a statement of the now familiar equation (cid:5)ν/ν0 = V /c. Here V is the relative speed in the line of sight, c is the speed of light, and ν0 is the light wave’s frequency for sources at rest.
关键词： frequency change,Doppler effect,astronomical spectroscopy,Christian Doppler,light waves
更新于2025-09-10 09:29:36
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Photon-recoil spectroscopy: Systematic shifts and nonclassical enhancements
摘要： In photon-recoil spectroscopy, signals are extracted from recoils imparted by the spectroscopy light on the motion of trapped ions as demonstrated by Hempel et al. [C. Hempel et al., Nat. Photon. 7, 630 (2013)] and Wan et al. [Y. Wan et al., Nat. Commun. 5, 3096 (2014)]. The method exploits the exquisite efficiency in the detection of phonons achievable in ion crystals and is thus particularly suitable for species with broad noncycling transitions where detection of fluorescence photons is impractical. Here we develop a theoretical model for the description of photon-recoil spectroscopy based on a Fokker-Planck equation for the Wigner function of the phonon mode. Our model correctly explains systematic shifts due to Doppler heating and cooling as observed in the experiment. Furthermore, we investigate quantum metrological schemes for enhancing the spectroscopic sensitivity based on the preparation and detection of nonclassical states of the phonon mode.
关键词： Wigner function,quantum metrology,Doppler effect,nonclassical states,Fokker-Planck equation,trapped ions,photon-recoil spectroscopy
更新于2025-09-09 09:28:46
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[IEEE 2018 International Conference on Indoor Positioning and Indoor Navigation (IPIN) - Nantes, France (2018.9.24-2018.9.27)] 2018 International Conference on Indoor Positioning and Indoor Navigation (IPIN) - Moving Object Tracking Based on High Precision Opto-Acoustic BPSK-CDMA Distance Measurement
摘要： Opto-acoustic indoor localization systems based on ultrasound and infrared allow the tracking of tools and hand movements in complex manual industrial assembly and handling processes, e. g. the application of glue or adhesive sealing material. However, this requires a localization system that is able to track the position of multiple objects simultaneously during movement when the system is affected by Doppler effects and noise. The amplitude shift keying (ASK) modulation method within the code division multiple access (CDMA) environment using Gold codes is focused in previous publications for unilateral distance measurement of non-moving objects. The novelty of this contribution is the implementation of the binary phase shift keying (BPSK) modulation method and the consideration of moving objects with a Doppler effect mitigation algorithm. This algorithm can be performed in real time with an acquisition and a tracking step. Moreover, BPSK provides a permanently available phase information that can be used for exact positioning of multiple moving transmitters and ensures more robustness to modeling errors and noise. In this publication unilateral distance measurement results for up to four moving objects simultaneously with various speeds up to 0.54 m/s are presented showing the superiority of BPSK-CDMA with Doppler effect mitigation (mean errors below 6.9 mm) compared to ASK-CDMA and BPSK-CDMA without Doppler effect consideration.
关键词： Doppler effect,time-of-flight,distance measurement,BPSK,ultrasound,Localization,CDMA,indoor positioning
更新于2025-09-09 09:28:46
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Optoacoustic microscopy at multiple discrete frequencies
摘要： Optoacoustic (photoacoustic) sensing employs illumination of transient energy and is typically implemented in the time domain using nanosecond photon pulses. However, the generation of high-energy short photon pulses requires complex laser technology that imposes a low pulse repetition frequency (PRF) and limits the number of wavelengths that are concurrently available for spectral imaging. To avoid the limitations of working in the time domain, we have developed frequency-domain optoacoustic microscopy (FDOM), in which light intensity is modulated at multiple discrete frequencies. We integrated FDOM into a hybrid system with multiphoton microscopy, and we examine the relationship between image formation and modulation frequency, showcase high-fidelity images with increasing numbers of modulation frequencies from phantoms and in vivo, and identify a redundancy in optoacoustic measurements performed at multiple frequencies. We demonstrate that due to high repetition rates, FDOM achieves signal-to-noise ratios similar to those obtained by time-domain methods, using commonly available laser diodes. Moreover, we experimentally confirm various advantages of the frequency-domain implementation at discrete modulation frequencies, including concurrent illumination at two wavelengths that are carried out at different modulation frequencies as well as flow measurements in microfluidic chips and in vivo based on the optoacoustic Doppler effect. Furthermore, we discuss how FDOM redefines possibilities for optoacoustic imaging by capitalizing on the advantages of working in the frequency domain.
关键词： Doppler effect,Frequency-domain,Multiphoton microscopy,Optoacoustic microscopy,Microcirculatory blood flow
更新于2025-09-04 15:30:14