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Introduction: The coronavirus disease 2019 (COVID-19) pandemic has affected billions of people worldwide, and the lessons learned need to be concluded to get better prepared for the next pandemic. Early identification of high-risk patients is important for appropriate treatment and distribution of medical resources. A generalizable and easy-to-use COVID-19 severity stratification model is vital and may provide references for clinicians. Methods: Three COVID-19 cohorts (one discovery cohort and two validation cohorts) were included. Longitudinal peripheral blood mononuclear cells were collected from the discovery cohort (n = 39, mild = 15, critical = 24). The immune characteristics of COVID-19 and critical COVID-19 were analyzed by comparison with those of healthy volunteers (n = 16) and patients with mild COVID-19 using mass cytometry by time of flight (CyTOF). Subsequently, machine learning models were developed based on immune signatures and the most valuable laboratory parameters that performed well in distinguishing mild from critical cases. Finally, single-cell RNA sequencing data from a published study (n = 43) and electronic health records from a prospective cohort study (n = 840) were used to verify the role of crucial clinical laboratory and immune signature parameters in the stratification of COVID-19 severity. Results: Patients with COVID-19 were determined with disturbed glucose and tryptophan metabolism in two major innate immune clusters. Critical patients were further characterized by significant depletion of classical dendritic cells (cDCs), regulatory T cells (Tregs), and CD4+ central memory T cells (Tcm), along with increased systemic interleukin-6 (IL-6), interleukin-12 (IL-12), and lactate dehydrogenase (LDH). The machine learning models based on the level of cDCs and LDH showed great potential for predicting critical cases. The model performances in severity stratification were validated in two cohorts (AUC = 0.77 and 0.88, respectively) infected with different strains in different periods. The reference limits of cDCs and LDH as biomarkers for predicting critical COVID-19 were 1.2% and 270.5 U/L, respectively. Conclusion: Overall, we developed and validated a generalizable and easy-to-use COVID-19 severity stratification model using machine learning algorithms. The level of cDCs and LDH will assist clinicians in making quick decisions during future pandemics. [ABSTRACT FROM AUTHOR]

Cell migration-inducing protein (CEMIP), also known as KIAA1199 and hyaluronan-binding protein involved in hyaluronan depolymerization, is a new member of the hyaluronidase family that degrades hyaluronic acid (HA) and remodels the extracellular matrix. In recent years, some studies have reported that CEMIP can promote the proliferation, invasion, and adhesion of various tumor cells and can play an important role in bacterial infection and arthritis. This review focuses on the pathological mechanism of CEMIP in a variety of diseases and expounds the function of CEMIP from the aspects of inhibiting cell apoptosis, promoting HA degradation, inducing inflammatory responses and related phosphorylation, adjusting cellular microenvironment, and regulating tissue fibrosis. The diagnosis and treatment strategies targeting CEMIP are also summarized. The various functions of CEMIP show its great potential application value. [ABSTRACT FROM AUTHOR]

Femtosecond light pulses carrying optical angular momentums (OAMs), possessing intriguing properties of helical phase fronts and ultrafast temporal profiles, enable many applications in nonlinear optics, strong-field physics, and laser micromachining. While generation of OAM-carrying ultrafast pulses and their interactions with matters are intensively studied in experiments, 3D characterization of ultrafast OAM-carrying light beams in spatiotemporal domain has, however, proved difficult to achieve. Conventional measurement schemes rely on the use of a reference pulsed light beam, which needs to be well characterized in its phase front and to have sufficient overlap and coherence with the beam under test, largely limiting practical applications of these schemes. Here a self-referencing set-up is demonstrated based on a tilted interferometer that can be used to measure complete spatiotemporal information of OAM-carrying femtosecond pulses with different topological charges. Through scanning one interferometer arm, the spectral phase over the pulse spatial profile can be obtained using the tilted interference signal, and the temporal envelope of the light field at one particular position around its phase singularity can be retrieved simultaneously, enabling 3D beam reconstruction. This self-referencing technique, capable of measuring spatiotemporal ultrafast optical-vortex beams, may find many applications in fields of nonlinear optics and light-matter interactions. [ABSTRACT FROM AUTHOR]

We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification, hollow-core fiber (HCF) and second harmonic generation processes. In this setup, the spectrum of an approximately 1.8 µm laser pulse has near 1 µm full bandwidth by employing an argon gas-filled HCF. Subsequently, after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair, 9.6 fs (~3 cycles) and 150 µJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated. The energy stability of the output laser pulse is excellent with 0.8% (root mean square) over 20 min, and the temporal contrast is >1012 at -10 ps before the main pulse. The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems. [ABSTRACT FROM AUTHOR]

The development of high-intensity ultrafast laser facilities provides the possibility to create novel physical phenomena and matter states. The timing fluctuation of the laser pulses is crucial for pump--probe experiments, which is one of the vital means to observe the ultrafast dynamics driven by intense laser pulses. In this paper, we demonstrate the timing fluctuation characterization and control of the front end of a 100-PW laser that is composed of a high-contrast optical parametric amplifier (seed) and a 200-TW optical parametric chirped pulse amplifier (preamplifier). By combining the timing jitter measurement with a feedback system, the laser seed and preamplifier are synchronized to the reference with timing fluctuations of 1.82 and 4.48 fs, respectively. The timing system will be a key prerequisite for the stable operation of 100-PW laser facilities and provide the basis for potential pump--probe experiments performed on the laser. [ABSTRACT FROM AUTHOR]

With the development of high-volume manufacturing for very-large-scale integrated circuits, the purity of the light source in the extreme ultraviolet lithography (EUVL) system needs to fulfil extreme requirements in order to avoid thermal effect, optical distortion and critical dimension errors caused by out-of-band radiations. This paper reviews the key technologies and developments of the spectral purity systems for both a free-standing system and a built-in system integrated with the collector. The main challenges and developing trends are also discussed, with a view towards practical applications for further improvement. Designing and manufacturing spectral purity systems for EUVL is not a single task; rather, it requires systematic considerations for all relevant modules. Moreover, the requirement of spectral purity filters drives the innovation in filtering technologies, optical micromachining and advanced metrology. [ABSTRACT FROM AUTHOR]

As intense, ultrashort, kHz-repetition-rate laser systems become commercially available, pulse cumulative effects are critical for laser filament-based applications. In this work, the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally. The pulse repetition-rate effect has negligible influence at the leading edge of the filament. Clear intensity enhancement from a high-repetition pulse is observed at the peak and tailing edge of the laser filament. As the repetition rate of the laser pulses increases from 100 to 1000 Hz, the length of the filament extends and the intensity inside the filament increases. A physical picture based on the pulse repetition-rate dependent 'low-density hole' effect on filamentation is proposed to explain the obtained results well. [ABSTRACT FROM AUTHOR]

A single-shot measurement of electron emittance was experimentally accomplished using a focused transfer line with a dipole. The betatron phase of electrons based on laser wakefield acceleration (LWFA) is energy dependent owing to the coupling of the longitudinal acceleration field and the transverse focusing (defocusing) field in the bubble. The phase space presents slice information after phase compensation relative to the center energy. Fitting the transverse size of the electron beam at different energy slices in the energy spectrum measured 0.27 mm mrad in the experiment. The diagnosis of slice emittance facilitates local electron quality manipulation, which is important for the development of LWFA-based free electron lasers. The quasi-3D particle-in-cell simulations matched the experimental results and analysis well. [ABSTRACT FROM AUTHOR]

Temporal contrast directly affects the interaction between ultraintense and ultrashort pulse lasers with matter. Seed laser sources with broad bandwidth and high temporal contrast are significant for overall temporal contrast enhancement. The technique of cascaded nonlinear processes with optical parametric amplification and second-harmonic generation is demonstrated for high temporal contrast seed source generation. Within 40 ps before the main pulse, the temporal contrast reaches over 1011. The pulse energy and duration of the high-contrast pulse are 112 µJ and 70 fs, respectively. Considering its high beam quality and stability, this laser source can serve as a high-quality seed for Nd:glass-based ultraintense and ultrashort pulse laser facilities. [ABSTRACT FROM AUTHOR]

A high-energy diode-pumped picosecond laser system centered at 1064 nm for optical parametric chirped pulse amplifier (OPCPA) pumping was demonstrated. The laser system was based on a master oscillator power amplifier configuration, which contained an Nd:YVO4 mode-locked seed laser, an LD-pumped Nd:YAG regenerative amplifier, and two double-pass amplifiers. A reflecting volume Bragg grating with a 0.1 nm reflective bandwidth was used in the regenerative amplifier for spectrum narrowing and pulse broadening to suit the pulse duration of the optical parametric amplifier (OPA) process. Laser pulses with an energy of 316.5 mJ and a pulse duration of 50 ps were obtained at a 100 Hz repetition rate. A top-hat beam distribution and a 0.53% energy stability (RMS) were achieved in this system. [ABSTRACT FROM AUTHOR]

Ultrafast multi-MeV high-flux gamma-ray beams have been experimentally produced via bremsstrahlung radiation of laser-accelerated energetic electrons through millimeter-thick copper targets. By optimizing the electron bunches to the charge of 10 nC in a clustering argon gas target, the obtained gamma-ray beam significantly increases to 1010 photons per shot. The gamma-ray beam spectrum has been measured using a differential filtering detector and has a broad spectrum up to 15 MeV, which is approximately consistent with the Geant4 simulation. The generated high-flux high-energy gamma-ray beams are promising sources for photonuclear reaction, non-destructive inspection and clinical applications. [ABSTRACT FROM AUTHOR]

ABSTRACT We report on a germanium Fabry-Perot interferometer heated with a Nd:YAG laser. The transmission property of the laser-heated germanium Fabry-Perot interferometer has been investigated experimentally and theoretically. The transmission of CO2 laser through the germanium Fabry-Perot interferometer varied with Nd:YAG laser heating. The theoretical results are in good agreement with the experimental results. The technique of laser-heated germanium Fabry-Perot interferometry is promising for applications in laser modulation and detection. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1009-1012, 2017 [ABSTRACT FROM AUTHOR]

Previous research on achieving the alignment of compression gratings has mainly focused on the parallelism of the gratings. We propose a promising method to achieve parallelism and especially accurately adjust the grating to its optimum working angle to achieve dispersion compensation. A spectrometer and a precisely adjustable mirror pair are cooperatively used to measure the wavelength of the light diffracted by the grating, satisfying the Littrow condition. Meanwhile, the tiny slit of the spectrometer can decrease the grating- tip and in-plane rotation error during the alignment procedure. Using this technique, the residual phase of the compressed pulse is optimized and the compressed pulse duration is 25.4 fs, which is 1.06 times that of the Fourier-transform-limited compressed pulse. [ABSTRACT FROM AUTHOR]

To compensate for the gain saturation effect in the high-energy laser amplifier, a modified polarization beam combination (PBC) method is introduced to reshape temporal waveform of the injected laser pulse to obtain a controlled high-energy laser pulse shape after amplification. One linearly polarized beam is divided into two orthogonal polarized beams, which spatially recombine together collinearly after propagating different optical paths with relative time delay in PBC structure. The obtained beam with polarization direction being rotated by the following half wave plate is divided and combined again to reform a new beam in another modified polarization beam structure. The reformed beam is injected into three cascaded laser amplifiers. The amplified pulse shape can be controlled by the incident pulse shape and amplifier gain, which is agreeable to the simulation by the Frank–Nodvik equations. Based on the simple method, the various temporal waveform of output pulse with tunable 7 to 20 ns pulse duration can be obtained without interferometric fringes. [ABSTRACT FROM AUTHOR]

Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron-positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8×1021 s-1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy. [ABSTRACT FROM AUTHOR]

We present an experimental investigation of optical spin orientation in colloidal CdS quantum dots (QDs) by a femtosecond laser pulse at room temperature. The spin carrier and its spin-generation process are clarified. Firstly, the observed spin signals of CdS QDs in time-resolved Faraday rotation measurements are shown to belong to electron carriers, by comparing the spin dephasing dynamics and Landé g factor between CdS QDs and bulk materials. Secondly, spin dynamics unaffected by the faster carrier recombination suggests that the spin-polarized electrons are not photoexcited but resident in the dots. Moreover, hole spins should dephase very fast compared with electron spins, otherwise the trion (two electrons with opposite spin orientations and one hole) recombination process will affect the resident electron spin signals. The electron spin is generated in a short time of which the excitation light is absorbed and the resident electron is excited to trion states, i.e., of pulse durations. Due to fast hole spin dephasing, trion recombination gives null spin signals, and the subsequent electron spin dynamics is controlled by its intrinsic mechanisms. [ABSTRACT FROM AUTHOR]

Based on a designed high-birefringence photonic crystal fiber with two zero-dispersion wavelengths (ZDWs), the effect of fiber dispersion, pump power and pump wavelength on the modulation instability (Mi) gain in the anomalous dispersion region is comprehensively analyzed in this paper. An asymmetric and broadband MI gain spectrum appears at the anti-Stokes band due to the different ZDWs along the fiber slow- and fast-axes. An optimal MI gain can be obtained when the pump wavelength (1675 nm) is slightly shorter than the second ZDW (1683 nm) and the pump power is 280 W. The optimal MI gain bandwidth finally reaches 152 nm and the gain profile is smoother. [ABSTRACT FROM AUTHOR]

Angular and energy distributions of fast electrons generated from the interaction of 60 fs, 795 nm laser pulses with aluminum targets have been experimentally investigated in various conditions. Increasing laser intensities from the nonrelativistic to the relativistic, a transition of the angular distribution of outgoing fast electrons from the specular reflection direction to the target normal has been observed for p-polarized laser irradiation. The fast electrons’ energy spectrum at high laser intensity, e.g., ∼2.6×1018 W/cm2, consists of two peaks, which are found to originate from the target normal with low energy and specular reflection direction with high energy, respectively. By adding a prepulse to generate preplasma, the electron yields at the direction of the reflected laser can be greatly enhanced, and a double-peak angular distribution is observed. Besides, a more collimated electron emission peak in the specular reflection direction can be obtained by employing a larger f-number focusing system. [ABSTRACT FROM AUTHOR]

Using a linearly chirped laser pulse to irradiate antireflection coated targets, the time-varying reflectivity of a plasma mirror (PM) has been measured at various laser intensities from 1012 to 1017 W/cm2. The onset of plasma generation as well as the formation process of a PM with the highest reflectivity has been observed. The rise time of the PM’s reflectivity reaching up to the maximum varies from 300–500 fs at lower laser intensities but goes up to 900 fs at higher intensity of >1016 W/cm2. This long rise time can be attributed to a slowly rising shoulder of the laser pulse, which will trigger the generation of preplasma well in advance of the laser peak. The detailed measurements on both time-integrated and time-resolved reflectivity of a PM, which is induced by p- and s-polarized laser pulses, respectively, indicate that an s-polarized pulse is favorable to obtain the maximal reflectivity and the best contrast improvement as well. This difference can be attributed to the weaker absorption and a smaller plasma scale length generated for s-polarization. [ABSTRACT FROM AUTHOR]

An experimental investigation on the interaction of an ultraintense femtosecond laser pulse at the intensity of 2×1017 W/cm2 (60 fs, 120 mJ at 800 nm) with clusters in a supersonic jet of deuterated methane gas has shown the generation of energetic deuterons and nuclear fusion events. The deuteron density and the average size of the clusters in the gas jet, as well as the fusion neutron yields under different backing pressures were measured simultaneously as a function of the time delays of the laser pulses with respect to the puffing of the gas jet. The results demonstrate that during the development of the gas jet expanding through a conical nozzle, the clusters grew up with time, and the average size of the clusters reached the maximum when the molecular density in the jet started to drop. The fusion neutron yields were found to increase with the larger average cluster size and the higher deuteron density, in accordance with the theoretical prediction. Experimental data indicate the existence of a ∼1 ms steady region in which the fusion neutron yields have reached the maximum of 2.0×105 per shot at the backing pressure of 74 bars. Consequently, an efficiency of 1.6×106 neutrons per joule of incident laser energy was realized. [ABSTRACT FROM AUTHOR]

A compact 10-TW/100-fs level ultrashort-pulse and ultra-intense laser system at 1064 nm based on optical parametric chirped pulse amplification (OPCPA) scheme is described, at which the pump and seed for the optical parametric amplification (OPA) process is optically synchronized. We investigated the output stability and the conversion efficiency of the system. Moreover, a design toward higher peak power output is given and an optically synchronized amplifier based on the concept of OPCPA at 800 nm is preliminarily explored. [ABSTRACT FROM PUBLISHER]

Laser wakefield acceleration of electrons well beyond 1 GeV and optical guiding of ultraintense laser pulses of peak powers up to 160 TW over a 4-cm long ablative capillary discharge plasma channel were experimentally demonstrated. Electron beams, with energies up to 1.8 GeV, were generated by using the 130 TW, 55 fs driving laser pulses. A comparison of oxygen-containing acrylic resin (C:O:H = 4:2:7) capillary and no oxygen-containing polyethylene (C:O:H = 1:0:2) capillary measurements suggests that the injection of electron into the laser wakefield is assisted by the ionization of oxygen K-shell electrons. [ABSTRACT FROM AUTHOR]

We present an intra-cavity spectral shaping method to suppress the spectral narrowing in a Ti:sapphire (Ti:Sa) regenerative amplifier. The spectral shaping is realized by manipulating the stored energies of two Ti:Sa crystals with orthogonal c-axes, changing the length of a quartz plate, and rotating a broadband achromatic half-wave plate. Using this method, in our proof-of-concept experiment, an 84-nm-(FWHM)-broadband amplified pulse with an energy gain larger than 106 is obtained, which supports a 17.8 fs Fourier-transform-limited pulse duration. The pulse is compressed to 18.9 fs. [ABSTRACT FROM AUTHOR]

The underlying mechanism of the spectral cleaning effect of the cross-polarized wave (XPW) generation process was theoretically investigated. This study shows that the spectral noise of an input spectrum can be removed in the XPW generation process and that the spectral cleaning effect depends on the characteristics of the input pulses, such as the chirp and Fourier-transform-limited duration of the initial pulse, and the modulation amplitude and frequency of the spectral noise. Though these factors codetermine the output spectrum of the XPW generation process, the spectral cleaning effect is mainly affected by the initial pulse chirp. The smoothing of the spectrum in the XPW generation process leads to a significant enhancement of the coherent contrast. [ABSTRACT FROM AUTHOR]

The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one-dimensional (1D) and two-dimensional (2D) Frantz–Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti:sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti:sapphire chirped pulse amplifier system. [ABSTRACT FROM AUTHOR]

A modified polarized beam combination technique is proposed for preserving the temporal waveforms of stimulated Raman scattering. 1064 nm pre-pulse pumping lasers prior to the main pumping laser with a delay time are generated and injected into a Ba(NO3)2 Raman medium to excite the crystal firstly. The influences of pre-pulse lasers with various energy levels on the temporal shapes of Raman lasers are investigated, and it is demonstrated that the temporal waveforms of the Raman laser are distorted once the energies of the pre-pulse are below and above the required energy for preserving the temporal shapes of Stokes radiation. It is also discovered that the temporal shape of the 1197 nm Raman laser cannot be perfectly preserved if the energy of the 1064 nm main laser is too low or the relative delay time is too large. Moreover, the optical conversion efficiency and Stokes laser energy obtained under pumping lasers with single and double intensity peaks are compared. [ABSTRACT FROM AUTHOR]