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Laser-wavelength and intensity dependence of electron-nuclear energy sharing in dissociative ionization of
摘要： We experimentally and theoretically study the photoelectron-nuclear energy sharing mechanism of the correlated dynamics between the photoelectrons and the fragmented ions in the dissociative ionization of H2 with respect to the laser intensity at the wavelengths λ = 395 nm and λ = 790 nm. We show that the prominent photoelectron-nuclear energy sharing along the back-diagonal lines is only observed for 395 nm at lower intensities, which is absent for increased intensities at 395 nm and for 790 nm lasers over a wide range of intensities. Based on a quantum mechanical model that includes the correlation between the photoelectron and the parent ion, we show that bond hardening has a significant effect on the photoelectron-nuclear energy sharing. The resonant states of the neutral hydrogen molecule during strong-field ionization and the distribution of vibrational states of molecular ions determine the joint energy spectrum of photoelectrons and nuclei. The study provides an intuitive and comprehensive description and understanding of the correlated photoelectron-nuclear dynamics in the dissociative ionization.
关键词： dissociative ionization,photoelectron-nuclear energy sharing,wavelength dependence,laser intensity,H2
更新于2025-09-23 15:21:01
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Diagnostics of peak laser intensity by pair production from thin foil target
摘要： It is known that in the small quantum parameter regime the Breit-Wheeler electron-positron pair creation cross section is extremely sensitive on the photon energy and on the background field. We present the dependence of positron yield on laser intensity in laser-foil interactions with the help of analytical theory and particle-in-cell simulaitons. These particles are emitted in a relatively narrow range of cone angles close to perpendicular direction relative to the laser beam axis. This allows for establishing an in situ intensity diagnostic by measuring the positron current in experiments where peta-watt class lasers are used.
关键词： high power lasers,QED in plasmas,laser intensity diagnostics
更新于2025-09-23 15:21:01
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The mean energy transfer and collisional absorption coefficient of high power laser in plasma
摘要： The absorption coefficient of high power laser incident normally onto a plasma medium is studied when electron energy distribution obeys non-extensive function. The variation of the absorption coefficient with the incident laser intensity is investigated for different electron temperatures as well as different non-extensive distribution parameter (q). The variation of the absorption coefficient with plasma density is also investigated for different q values for constant temperature. Furthermore the mean rate of energy absorption is evaluated as function of the incident laser intensity for different electron temperatures and q values. The results are compared with ones obtained in Maxwellian case and differences are shown in the corresponding diagrams.
关键词： Non-extensive distribution,Absorption coefficient,Inverse bremsstrahlung,Laser intensity,Maxwellian distribution
更新于2025-09-23 15:21:01
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Efficiency control of high-order harmonic generation in gases using driving pulse spectral features
摘要： The low conversion efficiency of high-order harmonic generation (HHG) in gases is an insurmountable limitation for many applications, where a considerable photon flux is an instrumental prerequisite. We present a study of the HHG conversion efficiency dependence on the driving laser intensity and analyze the conditions for optimal phase-matching in a loose focusing configuration and long generation medium using a Ti:Sapphire laser. Moreover, by determination of the influence of plasma effects on the driving laser pulse, we observe a correlation between the HHG conversion efficiency and the blueshift of the fundamental pulse. The maximal HHG conversion efficiency is achieved just before the driving laser spectrum is considerably affected by the plasma. Similar behavior is observed in HHG for different noble gases. In this respect, the appearance of a plasma-induced spectral shift in the driving laser might serve as an indication of a substantial loss of HHG conversion efficiency. Consequently, our findings can be exploited to obtain essential information about the laser-plasma interaction process during HHG and can pave the way for a more convenient control of optimal HHG conditions.
关键词： plasma effects,high-order harmonic generation,conversion efficiency,driving laser intensity,spectral blueshift,phase-matching
更新于2025-09-23 15:21:01
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Exploring phase contrast imaging with a laser-based K?± x-ray source up to relativistic laser intensity
摘要： this study explores the ability of a hard Kα x-ray source (17.48 keV) produced by a 10 TW class laser system operated at high temporal contrast ratio and high repetition rate for phase contrast imaging. For demonstration, a parametric study based on a known object (PET films) shows clear evidence of feasibility of phase contrast imaging over a large range of laser intensity on target (from ~1017 W/cm2 to 7.0 × 1018 W/cm2). To highlight this result, a comparison of raw phase contrast and retrieved phase images of a biological object (a wasp) is done at different laser intensities below the relativistic intensity regime and up to 1.3 × 1019 W/cm2. this brings out attractive imaging strategies by selecting suitable laser intensity for optimizing either high spatial resolution and high quality of image or short acquisition time.
关键词： biological imaging,laser intensity,phase contrast imaging,high repetition rate,Kα x-ray source
更新于2025-09-23 15:19:57
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Surface behavior of 16Cr3Al ODS steel—Effects of high laser intensity 1014 W/cm2 in ambiences of air, helium and vacuum
摘要： The behavior of 16Cr3Al ODS steel (oxide dispersion strengthened steel), widely employed structural fusion material, under high-intensity laser radiation with intensity up to 1014 W/cm2 was investigated in air, helium and vacuum surrounding. Employed system was 65 fs laser at 804 nm, with applied pulse energy up to 5.25 mJ. Morphological effects were studied – cracking, crater parameters (depth, cross-section), LIPSS (laser-induced periodic surface structures) formation at the crater periphery, hydrodynamic effects, as well as chemical variations on the surface. Ablation thresholds were also determined for all three ambiences (for 100 applied pulses), and they were 0.30 J/cm2, 0.23 J/cm2 and 0.39 J/cm2 in air, helium and vacuum, respectively. Plasma occurred in all experiments and it was most prominent in vacuum due to strongest laser-material coupling.
关键词： 1014 W/cm2 laser intensity,Laser-induced damages/craters,Nuclear material,Femtosecond laser surface modification,ODS steel
更新于2025-09-19 17:13:59
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Influence of Laser Intensity Fluctuation on Single-Cesium Atom Trapping Lifetime in a 1064-nm Microscopic Optical Tweezer
摘要： An optical tweezer composed of a strongly focused single-spatial-mode Gaussian beam of a red-detuned 1064-nm laser can con?ne a single-cesium (Cs) atom at the strongest point of the light intensity. We can use this for coherent manipulation of single-quantum bits and single-photon sources. The trapping lifetime of the atoms in the optical tweezers is very short due to the impact of the background atoms, the parametric heating of the optical tweezer and the residual thermal motion of the atoms. In this paper, we analyzed the in?uence of the background pressure, the trap frequency of optical tweezers and the laser intensity ?uctuation of optical tweezers on the atomic trapping lifetime. Combined with the external feedback loop based on an acousto-optical modulator (AOM), the intensity ?uctuation of the 1064-nm laser in the time domain was suppressed from ±3.360% to ±0.064%, and the suppression bandwidth in the frequency domain reached approximately 33 kHz. The trapping lifetime of a single-Cs atom in the microscopic optical tweezers was extended from 4.04 s to 6.34 s.
关键词： optical tweezer,suppression of laser intensity ?uctuation,parametric heating,atomic trapping lifetime
更新于2025-09-19 17:13:59
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[IEEE 2018 International Topical Meeting on Microwave Photonics (MWP) - Toulouse (2018.10.22-2018.10.25)] 2018 International Topical Meeting on Microwave Photonics (MWP) - Strategies for noise reduction of a dual-frequency VECSEL dedicated to cesium CPT clocks
摘要： We investigate the strategies to reduce the noise of a class-A dual-frequency vertical external cavity surface emitting laser (VECSEL) operating at Cesium clock wavelength. We focus mainly on the beatnote phase noise of the two orthogonally polarized modes emitted. Within the framework of coupled rate equations, we show that the phase noise spectrum of the beatnote is well described by considering both the phase–amplitude coupling and the thermal effects. The spearhead of this study consists in ?rst theoretically evidencing reduction strategies for the phase noise beatnote by optimizing the physical parameters of the model and then experimentally demonstrating its feasibility by using two in-phase fully–correlated beams pumping each mode separately. Possible ways to decrease the intensity noises are also identi?ed.
关键词： vertical external cavity surface emitting laser,Dual-frequency laser,intensity noise,cesium clock,phase noise
更新于2025-09-16 10:30:52
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Effect of Small Focus on Electron Heating and Proton Acceleration in Ultrarelativistic Laser-Solid Interactions
摘要： Acceleration of particles from the interaction of ultraintense laser pulses up to 5 × 1021 W cm?2 with thin foils is investigated experimentally. The electron beam parameters varied with decreasing spot size, not just laser intensity, resulting in reduced temperatures and divergence. In particular, the temperature saturated due to insufficient acceleration length in the tightly focused spot. These dependencies affected the sheath-accelerated protons, which showed poorer spot-size scaling than widely used scaling laws. It is therefore shown that maximizing laser intensity by using very small foci has reducing returns for some applications.
关键词： proton acceleration,focal spot size,ultrarelativistic laser-solid interactions,electron heating,laser intensity
更新于2025-09-16 10:30:52
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Laser Intensity Noise Suppression for Preparing Audio-Frequency Squeezed Vacuum State of Light
摘要： Laser intensity noise suppression has essential effects on preparation and characterization of the audio-frequency squeezed vacuum state of light based on a sub-threshold optical parametric oscillator (OPO). We have implemented two feedback loops by using relevant acousto-optical modulators (AOM) to stabilize the intensity of 795-nm near infrared (NIR) fundamental laser and 397.5-nm ultraviolet (UV) laser generated by cavity-enhanced frequency doubling. Typical peak-to-peak laser intensity fluctuation with a bandwidth of ~10 kHz in a half hour has been improved from ±7.45% to ±0.06% for 795-nm NIR laser beam, and from ±9.04% to ±0.05% for 397.5-nm UV laser beam, respectively. The squeezing level of the squeezed vacuum state at 795 nm prepared by the sub-threshold OPO with a PPKTP crystal has been improved from ?3.3 to ?4.0 dB around 3~9 kHz of analysis frequency range.
关键词： audio frequency,acousto-optical modulator (AOM),laser intensity noise,feedback loop,squeezed vacuum state of light
更新于2025-09-16 10:30:52