Plasma density transition-based electron injection in laser wake field acceleration driven by a flying focus laser

By using a high-intensity flying focus laser,the dephasingless[Phys.Rev.Lett.124134802(2020)]or phase-locked[Nat.Photon.14475(2020)]laser wakefield acceleration(LWFA)can be realized,which may overcome issues of laser diffraction,pump depletion,and electron dephasing which are always suffered in usual LWFA.The scheme thus has the potentiality to accelerate electrons to Te V energy in a single acceleration stage.However,the controlled electron injection has not been self-consistently included in such schemes.Only external injection was suggested in previous theoretical studies,which requires other accelerators and is relatively difficulty to operate.Here,we numerically study the actively controlled density transition injection in phase-locked LWFA to get appropriate density profiles for amount of electron injection.The study shows that compared with LWFA driven by lasers with fixed focus,a larger plasma density gradient is necessary.Electrons experience both transverse and longitudinal loss during acceleration due to the superluminal group velocity of the driver and the variation of the wakefield structure.Furthermore,the periodic deformation and fracture of the flying focus laser in the high-density plasma plateau make the final injected charge also depend on the beginning position of the density downramp.Our studies show a possible way for amount of electron injection in LWFA driven by flying focus lasers.

Clinical characterization of refractory virus-related inflammation inside aqueous outflow pathways in Chinese immunocompetent patients

To the Editor: Posner-Schlossmann syndrome (PSS), also known as glaucomatocyclitic crisis, is characterized by acute, unilateral, recurrent attacks of ocular hypertension, mild non-granulomatous anterior uveitis (AU), and spontaneous recovery. However, the etiology of this disease is unknown. Many mechanisms have been proposed including viral infection, autoimmune, autonomic dysregulation, allergic conditions and vascular endothelial dysfunction.[1] Topical anti-hypertensives and anti-inflammatory medications are typically prescribed to combat this disease. Repeated attacks may lead to longterm glaucomatous optic nerve damage over 5–10 years after the first episode. Because the pathophysiology is not completely understood, treatment and prevention of recurrences has proven to be difficult.

Generation of a curved plasma channel from a discharged capillary for intense laser guiding

Straight plasma channels are widely used to guide relativistic intense laser pulses over several Rayleigh lengths for laser wakefield acceleration.Recently,a curved plasma channel with gradually varied curvature was suggested to guide a fresh intense laser pulse and merge it into a straight channel for staged wakefield acceleration[Phys.Rev.Lett.120,154801(2018)].In this work,we report the generation of such a curved plasma channel from a discharged capillary.Both longitudinal and transverse density distributions of the plasma inside the channel were diagnosed by analyzing the discharging spectroscopy.Effects of the gas-filling mode,back pressure and discharging voltage on the plasma density distribution inside the specially designed capillary are studied.Experiments show that a longitudinally uniform and transversely parabolic plasma channel with a maximum channel depth of 47.5µm and length of 3 cm can be produced,which is temporally stable enough for laser guiding.Using such a plasma channel,a laser pulse with duration of 30 fs has been successfully guided along the channel with the propagation direction bent by 10.4◦.

Robust time reversal processing for active detection of a small bottom target in a shallow water waveguide

With the spatial-temporal focusing of acoustic energy,time reversal processing(TRP) shows the potential application for active target detection in shallow water.To turn the ‘potential’ into a reality,the TRP based on a model source(MS) instead of a physical probe source(PS) is investigated.For uncertain ocean environments,the robustness of TRP is discussed for the narrowband and broadband signal respectively.The channel transfer function matrix is first constructed in the acoustic perturbation space.Then a steering vector for time reversal transmission is obtained by singular value decomposition(SVD) of the matrix.For verification of the robust TRP,the tank experiments of time reversal transmission focusing and its application for active target detection are undertaken.The experimental results have shown that the robust TRP can effectively detect and locate a small bottom target.

Focusing with the decomposition of the time reversal operator method in noisy environments

This paper presents a detailed analysis of the effects of noise (reverberation) on the focusing performance of de-composition of the time reversal operator (DORT) in a noise-limited case and in a reverberation-limited case, respectively. Quantitative results obtained from simulations and experiments are presented. The results show the DORT method can be effi-ciently applied to target detection with enough source level to yield significant backscatter. For a target placed on the bottom, the influence of the reverberation on the focusing performance is slight. However, distinguishing between a target and constant backscattering returning from strong local clutter on the bottom (false alarms) needs further research.