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Zhao-Hua Wang,1,* Chang Shu,2,* Xiao Ran,1 Cui-Hong Xie,1 Lei Zhang2 1Department of Critical Care Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People’s Republic of China; 2Department of Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People’s Republic of China*These authors contributed equally to this workCorrespondence: Lei ZhangDepartment of Surgery, Tongji Hospital, 1095 Jiefang Avenue, Wuhan 430030, People’s Republic of ChinaTel +86-27-83665312Email zhangl@tjh.tjmu.edu.cnBackground: Coronavirus disease 2019 (COVID-19) is a worldwide pandemic outbreak with a high mortality. Prognostic factors of critically ill patients with COVID-19 have not been fully elucidated yet.Methods: In the present study, 59 patients with COVID-19 from the intensive care unit of the Caidian Branch of Tongji Hospital were enrolled. Epidemiological, demographic, clinical, laboratory, radiological, treatment data, and clinical outcomes were collected. Prognostic factors were statistically defined.Results: Of the 59 patients studied (67.4± 11.3 years), 38 patients were male, 51 had underlying diseases, and 41 patients died during admission. Compared with the survivors, the deceased patients were of older age, had more smoking history, severer fatigue, and diarrhea, a higher incidence of multiple organ injuries, more deteriorative lymphopenia and thrombocytopenia, remarkably impaired cellular immune response, and strengthened cytokine release. Age higher than 70 (OR=2.76, 95% CI=1.45– 5.23), arrhythmia (OR=4.76, 95% CI=1.59– 14.25), and a Sequential Organ Failure Assessment (SOFA) score above 4 (OR=5.16, 95% CI=1.29– 20.55) were identified as risk factors for mortality of patients.Conclusion: Critically ill COVID-19 patients aged higher than 70, arrhythmia, or a SOFA score above 4 have a high risk of mortality, and need prior medical intervention.Keywords: severe acute respiratory coronavirus 2, pneumonia, critically ill, mortality, prognostic factor

Si Wen,1,* Zhao-Hua Wang,2,* Cong-Xiao Zhang,1 Ying Yang,1 Qiu-Ling Fan1 1Department of Nephrology, First Hospital of China Medical University, Shenyang, People’s Republic of China; 2Affiliated Dalian Friendship Hospital of Dalian Medical University, Dalian, People’s Republic of China*These authors contributed equally to this workCorrespondence: Qiu-Ling FanDepartment of Nephrology, First Hospital of China Medical University, No. 155 Nanjing Bei Street, Shenyang 110001, People’s Republic of ChinaTel +86 13904012680Email cmufql@163.comBackground: Apoptosis has been repeatedly linked with diabetic kidney disease (DKD), which is a programmed cell death mediated by effector caspases-3, 6 and 7, targeting > 600 substrates. However, the pathophysiologic correlations of this process remain obscure. As a putative tumor suppressor, gasdermin E (GSDME) was recently reported to be cleaved by caspase-3 to produce a GSDME-N fragment which targets the plasma membrane to switch apoptosis to secondary necrosis. However, it remains elusive whether GSDME is involved in the regulation of DKD.Methods: To evaluate the therapeutic potential of caspase-3 inhibition in DKD, we administered caspase-3 inhibitor Z-DEVD-FMK to STZ-induced diabetic mice for eight weeks. Albuminuria, renal function, pathological changes, and indicators of secondary necrosis and fibrosis were evaluated. In vitro, human tubule epithelial cells (HK-2 cells) were subjected to high-glucose treatment. Secondary necrosis was determined by LDH release, GSDME cleavage, and morphological feature under confocal microscopy. Z-DEVD-FMK and GSDME inhibition by shRNA were administered to suppress the cleavage and expression of GSDME. Flow cytometry, cytotoxicity assay and immunoblot were used to assess cell death and fibrogenesis.Results: Caspase-3 inhibition by Z-DEVD-FMK ameliorated albuminuria, renal function, and tubulointerstitial fibrosis in diabetic mice. The nephroprotection mediated by Z-DEVD-FMK was potentially associated with inhibition of GSDME. In vitro, molecular and morphological features of secondary necrosis were observed in glucose-stressed HK-2 cells, evidenced by active GSDME cleavage, ballooning of the cell membrane, and release of cellular contents. Here we showed that caspase-3 inhibition prevented GSDME activation and cell death in glucose-treated tubular cells. Specifically, knocking down GSDME directly inhibited secondary necrosis and fibrogenesis.Conclusion: These data suggest GSDME-dependent secondary necrosis plays a crucial role in renal injury, and provides a new insight into the pathogenesis of DKD and a promising target for its treatment.Keywords: GSDME, DFNA5, secondary necrosis, diabetic kidney disease, Z-DEVD-FMK

Objective: To investigate the potential molecular mechanism of Xin Hui Tong Formula (XHTF) in the treatment of coronary heart disease (CHD) by using network pharmacology and bioinformatics. Methods: The targets network of CHD was constructed through Therapeutic Targets Database (TTD) and Drugbank database; The XHTF pharmacodynamic molecule-targets network and the XHTF pharmacodynamic molecule-CHD targets network were explored by the traditional Chinese medicine systems pharmacology database and analysis platform (TCMSP). And the multi-targets mechanism and molecular regulation network of XHTF in the treatment of CHD were explored from multiple perspectives by Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathway enrichment analysis. Results: A total of 88 CHD targets were screened out through the Therapeutic Targets and the Drugbank database. 393 compounds and corresponding 205 drug targets of XHTF were retrieved from TCMSP. A total of 13 known targets directly related to the development of CHD were retrieved from the disease-related databases: TP53, MAPK14, NFKB1, HSPA5, PLG, PTGS2, ADRB1, NOS2, CYP3A4, GRIA2, CYP2A6, GRIA1, PTGS1. XHTF also contained 118 drug targets that directly interact with CHD targets. GO enrichment analysis showed that the biological processes of 13 direct targets proteins were found to be mainly enriched in response to drug, cellular response to biotic stimulus, long-chain fatty acid metabolic process, fatty acid metabolic process and regulation of blood pressure. KEGG pathway enrichment analysis found that XHTF participated in the CHD pathological process mainly through retrograde endocannabinoid signaling, regulation of lipolysis in adipocytes, cAMP signaling pathway, chemical carcinogenesis and other pathways. Conclusions: XHTF plays a role in the treatment of CHD through multiple targets and multiple pathways, and provides a scientific basis for the theory of “virtual standard” in the treatment of CHD. Keywords: Xin Hui Tong Formula (XHTF), Coronary heart disease, Network pharmacology, Network analysis, Bioinformatics

Picosecond laser with high-repetition-rate and high pulse energy is widely favorite in many scientific and industrial applications. Some nonlinear crystals can be used to efficiently convert a near-infrared laser into a green laser or an ultraviolet laser which has a higher photon energy and a smaller focal area. Especially for high-quality and high-speed transparent hard material fabrication, green or ultraviolet picosecond laser has been found to possess unique advantages. In this paper, the experiments on high-efficiency second-harmonic-generation (SHG) and third-harmonic-generation (THG) by using a home-made all-solid-state picosecond laser amplifier and an LBO crystal are reported. The picosecond laser amplifier consists of a seed source, a regenerative amplifier and a two-stage single-pass amplifier. The seed source is a commercial all-solid-state picosecond oscillator with a pulse duration of 8.3 ps and a repetition rate of 68 MHz. The repetition rate is reduced from 68 MHz to 500 kHz by an electro-optic Pockels cell (PC), and the period doubling bifurcation is minimized by reducing the duration of high voltage in PC. Both the regenerative amplifier and the two-stage single-pass amplifier are pumped by three 30-W continuous-wave fiber-coupled laser diodes. After the regenerative amplifier, the seed laser is amplified to 4.86 W with a repetition rate of 500 kHz at 1064 nm. Then the laser power is increased to 23.2 W by a two-stage single-pass amplifier, and the M2 value of the amplified laser in the X direction and in the Y direction are 1.330 and 1.235, respectively. The final pulse duration is 13.4 ps, which is slightly stretched in the amplification chain compared with the seed pulse duration (8.3 ps). For high-efficiency SHG and THG from near-infrared to green and ultraviolet, we carefully study the optical characteristics of some nonlinear crystals, such as LBO, BBO, BIBO, CLBO, etc., and we find that the LBO crystal, which has a high damage threshold, small walk-off and high nonlinear coefficient, is the best choice for both SHG and THG. Then the parameters of the two crystals for SHG and THG are specially designed according to the phase matching condition, the walk-off and the laser parameter. As a result, a 4-mm-long type-I phase matching LBO with cutting angle of θ = 90° and φ = 11.6° is used for SHG, and a 3-mm-long type-II phase matching LBO with cutting angle of θ = 42.2° and φ = 90° is used for THG. Finally, we realize high-efficiency frequency conversion with SHG power of 12.7 W at 532 nm and THG power of 9.25 W at 355 nm. The corresponding optical-optical conversion efficiencies reach 54.7% and 39.6%, respectively.

Ultra-short and ultra-intense laser is one of the hottest research spot of laser technology and strong field physics, due to its challenging and the frontier application research. As the key specification of ultrafast ultrahigh intensity laser pulse, the contrast ratio is very influential on the effect of laser-matter interaction. To perform the laser-matter interaction experiments at a high power level, the contrast is required to be as high as 1010 to prevent preplasma dynamics. To solve these problems, one has proposed many methods to improve the contrast of ultrafast laser, such as using the saturable absorbers, double chirped pulse amplification, plasma mirrors and the cross-polarized wave (XPW) generation. The XPW technology can not only enhance the contrast of the pulse by 3-4 orders of magnitude without introducing any space dispersion, but also extend the output spectrum to support shorter pulse duration. The XPW is a nonlinear filter technique in third-order nonlinear crystal with anisotropic susceptibility. Because of its simple and all-solid-state structure, the XPW technique has become one of the most effective methods to enhance the temporal pulse contrast and deliver shorter pulse duration in the field of high peak-power ultrafast lasers. This method has been used in many large laser facilities under construction or upgrades, such as the Apollon and ELI, the contrast ratio as high as 1010 has been achieved. It is known that the conversion efficiency and spectral characteristics of XPW have a strong dependence on the spatial and temporal magnitudes of the input driving pulse. In our experiment, it is found that the various changes of the driven pulse properties have different influences on the characteristics of XPW pulses. The relationship between the linear dispersion of driven pulse and temporal property of XPW is investigated theoretically. In addition, an experiment on verifying the theory is conducted by taking advantage of a programmable acousto-optic dispersion filter. The experimental results fit well to the theoretical results while some new phenomena emerge when the intensity in the BaF2 crystal reaches a saturation threshold. The spectral broadening capability of XPW becomes stronger and exceeds a theoretical upper limit. The pulse width can also be compressed to shorter than the theoretical limit. It is found that there are significant differences in spectral shape and conversion efficiency between the XPW signals by applying the opposite linear chirps to the driving pulse. A further analysis and theoretical explanation of these new phenomena are also presented.

With advent of chirped-pulse amplification, the peak power of femtosecond laser pulse was reached to petawatt (PW) or hundreds of terawatt (TW). Many progresses of high-field physics and ultrafast dynamics in matter are achieved using TW or PW laser. Pre-amplifier is an exponential growth amplifier which is also a bridge between oscillator and power amplifier. The best choice of pre-amplifier is amplification in regenerative cavity, due to its high stability and beam quality. The quality of pre-amplified laser pulse is significant to efficiency and beam quality of the successive power amplifier. High energy pre-amplifier with high beam quality will reduce the requirement of pump laser in final power amplifier. But typical regenerative amplifier only support low output energy of few millijoule. Higher energy from only one regenerative amplifier is crucial to whole laser system. High energy regenerative amplifier can be achieved by increasing the size of TEM00 in cavity. A new femtosecond Ti:sapphire regenerative amplifier with large mode size was demonstrated in this letter. The regenerative cavity is designed as stable linear resonator in which end mirrors are planar, the diameter of beam waist in Ti:sapphire crystal is larger than 2 mm, which can support high energy pulse amplified in cavity. By matching the focal spot of pump laser with the size of mode and optimization of cavity, the output laser energy up to 17.4 mJ was achieved under the pump energy of 60 mJ at repetition rate of 10 Hz, which corresponds to the efficiency of 29%. The amplified laser pulse from regenerative amplifier was compressed in a grating-pair compressor. By carefully alignment of incident angle and distance between the two gratings of compressor, the shortest pulses duration of 40.6 fs and energy of 13.9 mJ are obtained, which is a little bit longer than Fourier-transform limit based on spectrum of laser. The dispersion in the CPA laser system was also analyzed, after optimization of compressor, there are still high order dispersions uncompensated, which results in the duration of compressed pulses longer than Fourier-transform limit. Based on this large mode size regenerative amplifier, peak power of 1.9 TW laser pulses which compressed pulse energy of 81.4 mJ in 43 fs were also further realized by following only one stage of multipass amplifier. The beam quality (M2) was measured to be 1.6 and 1.5 in X and Y directions respectively, and the energy stability is 2.15% (rms). The results show that this large mode size regenerative amplifier is an ideal choice of pre-amplifier in TW laser system.

本文采用连续钛宝石激光作抽运, 掺杂浓度为6 at.%、长度为2.7 mm的Tm:YAG陶瓷作增益介质, 通过引入半导体饱和吸收体获得了稳定的被动锁模运转. 实验中获得的激光锁模功率为 116.5 mW, 中心波长为2007 nm, 重复频率为109 MHz, 通过自行搭建的腔外非共线强度自相关测量得到的脉冲宽度是55 ps. A passively mode-locked Tm:YAG ceramic laser was demonstrated. Employing a 6 at.% Tm3+-doped sample with a length of 2.7 mm, we have realized stable mode-locked pulses with a repetition rate of 109 MHz by a semiconductor saturable absorber. A maximum output power of 116.5 mW was obtained at the central wavelength of 2007 nm. The corresponding pulse duration was determined to be 55 ps by a self-built noncollinear intensity auto-correlation setup. It is shown that Tm:YAG ceramics are excellent laser materials which can be used in ultrafast lasers with high-power and high-efficiency output. Published version

High energy and high repetition rate femtosecond Ti:sapphire lasers are widely used in isolated attosecond pulses and high-order harmonic generation. Enhancing the driving laser energy is a convenient and effective way to improve attosecond pulse energy. A 1 kHz or higher repetition rate millijoule level femtosecond Ti:sapphire amplifier is generally used to generate isolated attosecond. However, due to the limitation of its green pump laser energy, the energy of femtosecond Ti:sapphire laser is limited to several millijoules. Appropriately reducing the requirements for repetition rate, realizing high energy driving laser will significantly improve attosecond pulse energy and extend its application scope. Meanwhile, a 532 nm pump laser from frequency doubled 1064 nm Nd:YAG flash lamp pumped laser at 100 Hz repetition rate can achieve high pump energy with lower cost. Accordingly, we develope a 100 Hz repetition rate high energy amplifier based on Ti:sapphire crystal. The femtosecond amplifier system consists of oscillator, stretcher, ring cavity regenerative amplifier, four-pass amplifier and grating compressor. The ring cavity regenerative amplifier is the first amplifier as pre-amplifier, and the four-pass amplifier is the booster amplified-stage. 80 MHz seed pulse from the oscillator has a full width at half maximum bandwidth of 61 nm with a 20 fs duration. Then the seed pulses are stretched to 200 ps with a Martinez grating stretcher, rotated to vertical polarization and injected into the regenerative amplifier. The amplified uncompressed 1 kHz repetition rate laser pulses with 3 mJ pulse energy are selected to be 100 Hz and input into the four-pass amplifier. With a pulse energy of 75.1 mJ, wavelength at 532 nm flash lamp pumped pump laser at 100 Hz repetition rate, single pulse energy up to 25.4 mJ is obtained from a Ti:sapphire crystal, corresponding to a high energy conversion efficiency of 33.8%. We believe that higher energy should be possible if the pump energy can be further increased. After expanding the beam to 10 mm in diameter, the amplified chirped pulse is compressed using a four-pass, single grating compressor, with an overall efficiency of 72%. The highest pulse energy after compression is 18.3 mJ. For a fluctuation of the 100 Hz pump laser is as high as 3.4% for over 10000 shots, the 3.6% energy stability of the amplifier has a room to be improved. The typical spectrum bandwidth after the compressor is 39 nm, which can support transform-limited pulse duration of 32.8 fs. After fine dispersion compensation by the compressor, A pulse duration of 37.8 fs is measured using a single shot autocorrelator (Minioptic Technology, Inc). In addition, the spatial profile of the output beam from the compressor is measured using a commercial laser beam analyzer (Spiricon, Inc). The beam quality M2 factor are 1.8 and 1.6 in X and Y directions, respectively. In summary, a peak power of 0.48 TW compact 100 Hz femtosecond laser with pulse duration of 37.8 fs, pulse energy of 18.3 mJ is achieved from a two-stage amplifier system based on Ti:sapphire crystal. We believe that with a more stable and better spatial profile pump source, even better performance can be obtained by this scheme. Nevertheless, the current results show that this system should be favorable for high energy attosecond pulse generation and further amplification such as Terawatt system.

High average power femtosecond lasers based on Ti:sapphire are widely used in strong-field physics and ultrafast dynamics.Continued advances include isolated attosecond pulse generation,few-cycle pulse generation,ultrafast spectroscopy,time-resolved photo-chemical reaction dynamics and laser micro-machining benefit greatly from use of such laser systems.The regenerative amplifiers are mostly utilized and have inherent advantages over multipass ones for applications in chirped pulse amplification.In this paper we describe a design,performance,and the characterizations of a novel linear cavity regenerative amplifier which has produced 4.8 W average power with 35 fs pulse durations at 1 kHz repetition rate. The main difficulty in designing and constructing a high average power Ti:sapphire regenerative cavity is thermal lensing effect.In order to generate amplified pulses with an output power exceeding 5 W at 1 kHz,a green pump power higher than 20 W is required.Meanwhile,the focal pump beam diameter on the surface of Ti:sapphire crystal should have sub-millimeter mode size to demonstrate large pump fluence,inducing a focal length of a thermal lens about 100 mm,i.e.,which is much less than the scale of the cavity length.For our experiments,a cavity mode size adjustable geometry is employed to counteract thermal lensing effect and to optimize the conversion efficiency of the amplifier.We first characterize the cavity stability by applying the well-known ABCD matrix formalism.The cavity consisting of R=900 mm concave mirror,an 2=800 mm lens and a plane mirror has two stability ranges with increasing the focal length of the thermal lens.In order to obtain a highest thermal tolerance,the optimal cavity parameters are resolved when two stability zones merge into one.After characterizing the cavity in detail,we calculate the cavity mode and the pump beam size at the position of the Ti:sapphire rod as a function of the thermal focal length.The optimal mode radius occurs at 312 m,corresponding to the intersection point of two curves.Stability curve exhibits a weak thermal sensitivity which is defined as the change of radius of cavity mode size per unit focal power change of thermal lens, keeping well below 10 m/D in a range of 2 D-4 D.The calculated results show that the active compensation for thermal lens focal length from 100 mm to could be achieved by adjusting the lens position,without changing the cavity. 20 fs,3 nJ pulses at a repetition rate of 82 MHz produced by a home-made Kerr-lens mode-locked oscillator are first sent to a Martinez stretcher by using a 1200 lines/mm holographic reflectance grating,which temporally stretches the laser pulses to 200 ps.The seed pulses out of the stretcher is then injected into the regenerative cavity depicted above. The 20 mJ pumping energy at 1 kHz is focused through the R=900 mm concave mirror into a 10 mm Brewster-cut Ti:sapphire rod,which is cooled to 250 K by thermoelectric elements.Condensation was avoided by placing the crystal into a small evacuated chamber.Mode matchings of pump and laser beam are found to be of critical importance for high energy extraction efficiency and high beam quality.In our experiments it is accomplished by fine adjusting the F=800 mm cavity lens and the pump beam size.The amplified power of 6.5 W at 1 kHz is obtained with minimum beam distortion,giving a 33.6% slope efficiency.The trapped pulse is built-up quickly and saturated after 8-round trips. The beam size of the amplified laser is expanded to 15 mm in diameter before compressor.A transmission efficiency of 73.8% is achieved through the grating-pair Treacy-type compressor,leading to a 4.8 mJ pulse energy.The grating has a groove density of 1500 lines/mm,and the compressed output spectrum has a full width at half maximum of 29 nm. The pulse duration measurement is performed by using an interferometric autocorrelation.As a result,a typical autocorrelation trace corresponding to a 35 fs pulse width is displayed,and agrees well with the 32 fs transform limit.The far-field beam profile after the compressor is round and Gaussian in both s and p planes,respectively.This scheme is also sufficiently reliable and robust so that no components of the laser system were damaged over a year of operation. In summary,the theoretical analysis and experimental results show that the regenerative cavity developed in this work exhibits a high conversion efficiency and an extraordinary thermal stability,and it is very suitable for high power and high efficient amplification of femtosecond Ti:sapphire pulses.

A long-term stable sub-8 fs Ti:sapphire oscillator based on domestic chirped mirrors is reported. It outputs 300 mW mode-locked pulses at 86 MHz under 4 W pump power. The second order and third order of dispersion introduced by the components of the oscillator are analyzed. Two pairs of domestically designed and fabricated chirped mirrors are utilized to compensate the dispersion introduced by the crystal and the air in cavity. By precisely controlling the dispersion of chirp mirrors, the output pulses have an ultra-broad bandwidth exceeding 150 nm (FWHM) without the insertion of wedges. With the assistance of extra-cavity dispersion compensation, a pulse duration of 7.9 fs is achieved. This is the shortest pulse duration ever reported by using domestic chirped mirrors, and the shortest pulse duration achieved without intra-cavity wedges, to the best of our knowledge. Structure design and electronic feed-back loops are employed to improve the stability of the oscillator passively and actively, respectively. With the assistance of piezoelectric ceramic, the power stability within 24 h is measured to be 0.6%, which is significantly better than that without them.

A novel design of X-ray spectrometer is implemented, using a high efficiency HOPG (highly oriented pyrolitic graphite) Bragg crystal. The spectral resolution of it can reach above 350 with energy ranging from 6.891 to 9.193 keV, theoretically. And the efficiency are 3 order of magnitude higher than the ordinary X-ray crystal spectrometer. Application of this instrument is demonstrated in high intensity laser-foil interaction experiments. It is shown that HOPG spectrometer has much lower threshold of X-ray intensity than ordinary one. The spectral resolution for 8.048 keV (Cu Kup -line) can reach 40 eV, which gives the spectral resolution 200.

We have investigated the vibrational sensitivity of a horizontal-mounted spherical reference cavity, which can be applied to develop an ultra-stable laser. Effects of different magnitudes of height and area as well as acceleration of the cavity support points on the length variation of the cavity are studied. When the cavity support points are totally constrained, the vibration sensitivity can be reduced to below 3.0×10-10/g. After performing extensive numerical simulations, we can find the optimal support position. According to the obtained results we present the mounting scheme of the spherical cavity. Taking into consideration the machining errors, near-horizontal mounting, and unsymmetrical mounting of the cavity, we can describe quantitatively the length variation of the cavity caused by these three factors. We also discuss the contribution of the second order effect to the length variation of the cavity.

In engineering applications, many measurements of physical quantities can be converted into the problems of frequency estimation. The current frequency estimators are mainly divided into two categories: iterative approaches and direct approaches. However, iterative approaches are not suitable for rapid physical measurement occasions due to its complicated process. But most of the direct approaches are the biased estimators, which are incapable of providing quantitative estimates of variance expression. To enhance the accuracy of the direct frequency estimator and derive the closed-form theoretic expression of the estimated error variance, this paper proposes a novel phase difference frequency estimator based on the forward and backward sub-segmenting. This estimator implements forward and backward fast Fourier transform (FFT) on the given samples separately, and then extracts the phase difference from the peak FFT bins of these two sub-segments to estimate the frequency. And it is emphasized that the proposed method is an unbiased frequency estimator, whose closed-form theoretic expression of the frequency estimated error variance is also derived. Moreover, simulation not only verifies the correctness of this closed-form expression but also proves that the proposed frequency estimator's mean square error is closer to the Cramer-Rao lower bound than that of apFFT/FFT phase difference estimator and Candan estimator. In conclusion, the proposed estimator has higher accuracy in measuring frequencies and has a wide application prospect.

Based on chirped-pulse amplification technology, a ring cavity Ti:sapphire regenerative amplifier with high output energy is demonstrated. Under the 532 nm pump energy of 33.1 mJ at a repetition rate of 100 Hz, the chirped laser pulse with energy of 9.84 mJ is obtained, corresponding to a slope efficiency of 33.1%. Instead, using the pump laser with energy of 32.0 mJ at a repetition rate of 10 Hz, we also obtain 9.64 mJ pulse energy with a corresponding slope efficiency of 36.8%. By optimizing the dispersion among all optical materials, stretcher and compressor, the shortest pulse has an energy of 6.36 mJ and a pulse width of 59.7 fs, and the energy fluctuation is 1.85 % (RMS) over 4000 shots after the compressor. The performances show that it may pave the way for ultrafast applications and serves as a front stage toward TW even PW laser system with high contrast ratio.

We set up a multi-wavelength ultraviolet terawatt-order chirped pulse amplification(CPA) system according to the CPA technology and the frequency conversion technology. The system offers 1Hz, 5Hz and 10Hz high energy ultraviolet pulses by precise time synchronization among 5 repeat frequencies. The RMS of output energy fluctuation rate of CPA is less than 2% with using a pre-amplified system of energy fluctuation rate less than 0.3% RMS and a time synchronizer with time jitter less than 3 ns. The multi-wavelength high energy ultraviolet pulses with 64 mJ/400 nm,16 mJ/267 nm and 5 mJ/205 nm are obtained, and their corresponding peak powers reach the terawatt level.

According to the theory of chirped pulse amplification (CPA), we analyze numerically the gain characteristic of laser pulses in multi-pass amplifier. A CPA Ti:sapphire laser with 10-pass scheme is designed and built. The experimental result shows that the contrast ratio of the femtosecond pulse is obviously enhanced by two orders from 10-5 to 10-7 under a pump flux of 1.6 J/cm2. This work demonstrates that the contrast ratio of the amplified femtosecond laser pulse could be effectively improved by multi-pass preamplifier.

This paper reports our experimental research on the laser contrast ratio enhancement in the XL-Ⅲ (eXtreme Light Ⅲ) facility with the technology of cross-polarized wave (XPW) generation. Based on the theoretical analysis of the relerant principles, we introduced an XPW filter in the facility, which was upgraded with a double chirped pulse amplification (DCPA) scheme. Under optimized system design and alignment, we measured the conversion efficiency from fundamental wave to cross-polarized wave to be higher than 10%. The pre-pulses in nanosecond scale were deeply suppressed and the contrast ratio in picosecond scale was enhanced from 10-5 to 10-7. Our results show the XPW generation provides an effective technique to improve the contrast ratio of a Chirped-pulse amplification laser system, which is a key issue in ultrahigh intensity laser-matter researches.

The pulse width generated by an ultra-broad-bandwidth Ti: sapphire oscillator is measured using SPIDER technique. The measurement result is 7.86 fs, which is, as presently reported in China, the shortest pulse output directly from an oscillator in which only chirped mirrors was used to compensate for the laser dispersion. Layout of the oscillator and the SPIDER setup are introduced in details, and the spectral phase of the laser pulse obtained through calculation is discussed.

We triggered and guided the stationary electric field discharges in 3—23 cm long air gaps by using plasma channels produced by 40mJ ultrashort laser pulses. We have observed that the plasma channel reduced the discharge breakdown voltage to 40% of its natural value. By analyzing the delay between the laser pulse and the white light emission of discharge, we evaluated the speed of the stepped leader with laser guiding to be about 107 cm/s.

As a novel inner surface processing method, grid enhanced plasma source ion implantation (GEPSII) method can realize uniform inner surface ion implantation of a metal tube and metal binary compound can be produced. In the experiment, three 0.45% carbon steel (45-steel) work pieces were axially put on the inner surface of the tube, and golden titanium nitride (TiN) films were produced on the work pieces by GPSII. Structure analysis shows that the TiN films have the preferred crystal faces (111) and (200), and the depth of the films is about 20 nm with partial embedding in the substrate. Analysis on the electrochemistry corrosion, hardness and friction of the work pieces indicates that the surface property of the 45-steel has been greatly improved by the protective TiN film, and very good axial uniformity has been obtained.

THz (terahertz) properties of MgF2 crystal (sample 1) and MgF2 : Co crystal (sample 2) is measured using transmission THz time domain spectroscopy in the frequency range between 0.5 and 2.5 THz. The absorption coefficients a(v) of sample 1 increases and has a maximum, 24 cm(-1) with increasing frequency v from 0.5 THz to 2.5 THz. The absorption coefficient of sample 2 is much larger than that of the sample I, and its absorption band edge of the crystal lattice shifts to lower frequency side because of the dopant Co. Moreover, there is an absorption peak at 1.9THz and the absorption coefficient is greater than 70 cm(-1), the force constant K of F- -Co2+ ionic chemical bond stretch vibration calculated from this peak is 3.40 x 10(-2) N/cm. The THz spectroscopy can be an important technique for research of chemical bond in crystal. Real dielectric functions between 0.5 and 2.5 THz of the two samples are calculated by relations between optical constants. The epsilon(1) (v) of sample 1 varies from 4.67 to 4.73 and epsilon(1) (v) of sample 2 varies from 4.62 to 5.01.

The characteristics of Kα X-ray sources generated by p-polarized femtosecond laser-solid interactions are experimentally studied in the relativistic regime. By use of knife-edge image technique and a single-photon-counting X-ray CCD camera, we obtaine the source size, the spectrum and the conversion efficiency of the Kα X-ray sources. The experimental results show that the conversion efficiency of Kα photons reaches an optimum value of 7.08×10-6/sr at the laser intensity of 1.6×1018W/cm2, which is different from the Reich's simulation results (Reich et al., 2000 Phys. Rev. Lett. 84 4846). We find that about 10% of laser energy is converted into the forward hot electrons at the laser intensity of 1.6×1018W/cm2.

The angular distribution and energy spectrum of hot electrons produced in the interaction of ultra-short ultra-intense laser pulses with solid foil targets are investigated. Results show that bath the angular distribution and the energy spectrum reveal anisotropic behavior. This anisotropy is believed to be related to the electron generation mechanism. The existence of energy anisotropy explains why different experimental groups obtained quite different elctron temperatures under the same laser intensity.

Nanocomposite films composed of Ag particles embedded in BaTiO3 matrix were grown on MgO(100) substrates by pulsed laser deposition. The structures of the films were determined by X-ray diffraction. The size and shape of the Ag particles were observed by transmission electron microscopy. The X-ray photoelectron spectroscopy results showed that Ag is in the metallic state. The optical absorption properties were measured from 300 to 800 nm, and the absorption peaks due to the surface plasmon resonance of Ag particles were observed. With increasing annealing temperature and Ag concentration, the peak absorption increased and shifted to longer wavelength (red-shift)

Energy spectrum and angular distribution of fast electrons are measured in the interaction of linearly (P and S) and circularly polarized femtosecond laser pulses with an aluminum target. It is interesting to note that the angular distribution of backward going electrons is unique for S and circular polarization. For S polarization, the angular distribution of fast electrons can be explained by taking account of the surface magnetic field qualitatively.

A long plasma channel can be formed when ultra-intense femtosecond laser pulse propagate, in air. We measured the value of the resistivity of the plasma channel and the contact resistance between the plasma channel and the electrodes. We also investigated the main factors affecting the resistivity of the plasma channel.

Strong third-order harmonic (TH) emission is observed from long plasma channels formed when intense femtosecond laser pulses propagate in air. The conversion efficiency between the fundamental wave and the TH emission is roughly constant over the length of the plasma channels. The divergence angle of the TH emission in the conical emission of the plasma channels is also investigated, which is in good agreement with calculations.