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Femtosecond pulse measurement of ultrafast spectrum is one of the important research directions in the ultrafast laser field. The conventional femtosecond pulse autocorrelation method is implemented by measuring the autocorrelated frequency-doubling signal, and the frequency-doubling signal has wavelength selectivity, so the femtosecond pulse measurement for the case of different central wavelengths needs to replace different frequency-doubling crystals, which is very inconvenient. This paper reports a kind of modified transient grating frequency resolution optical gating for measuring the femtosecond pulses. The method combines frequency-resolved optical gating (FROG) method with four-wave mixing. Its basic process is to divide the pulse to be measured into three beams. Two of the pulses can reach spatiotemporal coincidence on optical medium through precise delay control and focus. The other pulse interacts with the transient grating, and serves as the detection light to produce signal light. The spectrum and delay time of the signal light are measured by a spectrometer, and the spectrum and electric field information of the femtosecond pulse to be measured are obtained through the inversion iterative algorithm. Because this method only needs the power density of the measured light to reach the third-order nonlinear effect, it can be applied to the femtosecond pulse measurement of any central wavelength. We use this method to measure the femtosecond pulses with the central wavelengths of 800 nm and 400 nm respectively, and the ultra-wide spectrum femtosecond pulses with the period magnitude of sub-10 fs, and compare the measurement results with the results obtained with the conventional interferometric autocorrelation instrument. They are basically consistent. The experimental results show that our frequency-resolved optical switching method based on transient grating is very effective for measuring the femtosecond pulses with different central wavelengths and pulse widths.

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.

This paper reports that a 5-cm length birefringent photonic crystal fibre is used to tune the output frequency of unamplified 10-fs Ti:sapphire pulses. The zero dispersion of the fibre is at 823 nm and 800 nm for slow and fast fundamental modes, respectively. It is demonstrated that efficient upshift of the output frequency can be achieved when the pumped radiation is polarized along the slow axis of the fibre. When the average input power reaches 320 mW, about 60% of the output energy is located in one peak at 600 nm and is accompanied by depletion of the pulse inside the anomalous dispersion region.

A compact femtosecond Ti:sapphire laser resonator consisting of three chirped mirrors and one output coupler was designed. By accurately balancing the intracavity dispersions between Ti:sapphire crystal, air and chirped mirrors, we directly generated the laser pulse shorter than 7 fs at the average power of 340 mW with 3.1 W pump. The repetition rate of the laser oscillator is 173 MHz at the centre wavelength of 791 nm, and the ultrabroaden spectrum covers from 600 nm to 1000 nm. To the best of our knowledge, this is the simplest laser resonator capable of generating sub-10 fs laser pulse.

We report the properties of a compact diode-pumped continuous-wave Nd:GdVO4 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2 at.% Nd-doped Nd:GdVO4 laser, 1.54 W output laser power is achieved at 912 nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4 W. With 0.3 at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064 nm or 912 nm or the dual-wavelength emission at 1064 nm and 912 nm by controlling the incident pump power. From an incident pump power of 11.6 W, the 1064 nm emission between 4F3/2 and 4I11/2 is suppressed completely by the 912 nm emission between 4F3/2 and 4I9/2. We obtain 670 mW output of the 912 nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4 W. Using a Nd:GdVO4 laser with 0.4 at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064 nm or the dual-wavelength emission at both 1064 nm and 912 nm by increasing the incident pump power. We observe a strong competition process in the dual-wavelength laser.

The characteristics of hot electrons produced by p-polarized femtosecond laser-solid interactions are studied. The experimental results show that the outgoing electrons are mainly emitted in three directions: along the target surface, the normal direction and the laser backward direction. The electrons flowing along the target surface are due to the confinement of the electrostatic field and the surface magnetic field, while the electrons in the normal direction due to the resonant absorption.

We investigate the effects of confined laser ablation on laser plasma propulsion. Compared with planar ablation, the cavity ablation provides an effective way to obtain a large target momentum and a high coupling coefficient. When laser pulses are focused into a cavity with 1 mm diameter and 2 mm depth, a high coupling coefficient is obtained. By using a glass layer to cover the cavity, the coupling coefficient is enhanced by 10 times. Meanwhile, it is found that with the increase of the target surface size, the target momentum presents a linear increase.

Long plasma channels induced by femtosecond laser pulses in air are diagnosed using the sonographic method. By detecting the sound signals along the channels, the length and the electron density of the channels are measured. Refocusing is also observed at different laser energies and different focal lengths. We find that the sonographic method has manifest advantages compared to other techniques.

Spatial distribution of hot electrons with energies above 50 keV are investigated by an ethanol micro-droplet spray irradiated by linearly and elliptically polarized 150 fs laser pulses at an intensity of 1016W/cm2. Two symmetric hot electron jets with respect to the laser propagation direction are observed in the polarization plane for a linearly polarized laser field and in the plane of the long electric vector for an elliptically polarized laser field, respectively. Particle-in-cell simulations suggest that the resonance absorption on the spherical surface of the droplets is mainly responsible for the generation of the double-jet emission of hot electrons.

Intense few-cycle pulses are widely used in transient light synthesis,high harmonic generation (HHG) and especially in isolated attosecond pulse generation.To obtain intense few-cycle pulses,the intense supercontinuum is needed.The traditional way to generate intense supercontinuum is using rare gas filled hollow-core fibers.Since the input energy of hollow-core fiber system is limited to a level of tens of mJ,it is necessary to find new ways to achieve energy scaling.In this paper we demonstrate the efficient generation of supercontinuum by solid thin plates,compression and its application in HHG. The Ti:sapphire laser used in the present experiment emits 0.8 mJ in energy with a duration of 30 fs at 1 kHz.After passing through a 3:1 telescope,the beam has a diameter changed from 12 mm to 4 mm.Then the laser is focused by an f=2000 mm lens into a 600 m-diameter spot.After propagating through 7 fused silica plates placed at Brewster's angle (55.5) with a thickness of 0.1 mm,the 0.7 mJ octave spanning supercontinuum is achieved,corresponding to an efficiency of 87.5%.The first three plates are placed at 31,11,2.5 mm in front of the beam waist,and the last four plates are placed at 2,7,12,17 mm behind the beam waist respectively.With a pair of wedges and 4 pairs of chirped mirrors,the 0.68 mJ supercontinuum is compressed to a duration of 6.3 fs,which is measured by TG-FROG. The 0.5 mJ,6.3 fs pulse is used to perform high-harmonic generation experiment.The beam diameter is 150 m when focused by an f=400 mm lens,with a laser intensity of 8.11014 W/cm2.The 1 mm Ne gas jet is used to perform HHG experiment with a back pressure of 300 mbar.To block the near-infrared light,a 150 m Zirconium foil is placed behind the gas jet.Then the XUV spectrum is detected by a spectrometer,which consists of a flat field grating and a CCD camera.For driving pulses of few-cycle regime without dispersion,the cutoff spectrum of HHG is continuous.But when the pulse is stretched by positive or negative dispersion,the cutoff spectrum turns discrete.The HHG result is that the cutoff region is continuous when the wedge is in a certain place.Then by increasing or reducing the insertion of the wedge,the cutoff spectrum becomes discrete.Our result is consistent with HHG generated by few-cycle pulses. In conclusion,we demonstrate high-harmonic generation based on supercontinuum generated by solid thin plates. The 0.7 mJ supercontinuum is achieved when 0.8 mJ pulses are injected to 7 thin fused silica plates.The supercontinuum is compressed to 0.68 mJ,6.3 fs.The 0.5 mJ,6.3 fs pulse is used to perform HHG experiments.The HHG result was consistent with few-cycle driving pulses.Our research indicates that solid state supercontinuum has great potential applications in HHG and isolated attosecond pulse generation.

An optical pulse autocorrelator for rapid and slow scanning is described in this paper. Using an audio loudspeaker on one arm, an interferometric rapid-scanning signal of the output from a high-repetition laser oscillator is obtained. However, by adjusting the positions of the mirrors and using a step-motor on another arm, the intensity autocorrelation function of the output from a low-repetition laser amplifier can be easily measured. Using all-reflecting optics and an adequate nonlinear crystal, the whole instrument is very compact and has been used to measure sub-20 fs light pulses in both configurations with excellent agreement. In the slow-scanning configuration, a pulse train as long as 500ps has been determined. Using this autocorrelator, the home-made JIGUANG-I CPA laser facility was characterized for its pulse duration evolution.

The laser properties of the Nd:YGG crystal are investigated. The absorption spectrum from 500 to 900 nm and emission spectrum from 850 to 1400nm of Nd:YGG are measured. As much as 1.35 W output power of fundamental laser operating at 935 and 938 nm with a slope efficiency of 15.7% and 105 mW output power of frequency doubled blue laser are successfully obtained.

We report an efficient pumping scheme which involves a direct excitation of the upper lasing level of a four-level laser in a Nd-doped Ca3(NbGa)2-xGa3O12 (Nd:CNGG) by using a tunable Tr.sapphire, 700–920 nm, cw pump source. The slope efficiency is improved from 10.5% of the traditional band pumping at 808nm to 21.8% of the direct pumping at 882 nm. The influence of pumping wavelength on lasing is discussed. We present a scheme of double pumping for lasing.

We report a highly efficient and high power self-starting femtosecond Cr:forsterite laser pumped by a 1064-nm Yb doped fibre laser. Five chirped mirrors are used to compensate for the intra-cavity group-delay dispersion, and the mode-locking is initiated by a semiconductor saturable absorber mirror (SESAM). Under pump power of 7.9 W, stable femtosecond laser pulses with average power of 760mW are obtained, yielding a pump power slope efficiency of 12.3%. The measured pulse duration and spectral bandwidth (FWHM) are 46 fs and 45nm; the repetition rate is 82 MHz.

We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti:sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300 nm and from 2080 to 2930 nm, respectively, by changing the pump wavelength and the OPO cavity length. The maximum signal output power of 130 mW at the wavelength of 1225 nm is obtained, pumped by 900 mW of 800 nm laser radiation. This corresponds to a total conversion efficiency of 22.1%. The signal pulse duration is measured to be 167 fs by intensity autocorrelation with chirped mirrors for intracavity dispersion compensation.

A compact laser diode-pumped solid-state Nd:LuVO4 acousto-optic Q-switched laser is demonstrated at 916 nm of a quasi-three level for the first time. A pulse width of 130 ns is observed when the pulse-repetition frequency is 10 kHz. The laser experiment shows that the Nd:LuVO4 crystal can be used for efficient diode-pumped Q-switched lasers.

A stable continuous wave mode-locked picosecond Ti:sapphire laser by using a fast semiconductor saturable absorber mirror (SESAM) is demonstrated. The laser delivers pulse width of 20 ps at a central wavelength of 813 nm and a repetition rate of 100 MHz. The maximum output power is 1.34 W with pump power of 7 W which corresponds to an optical–optical conversion efficiency of 19.1%.

We report the compact diode-pumped continuous-wave (CW) Nd:LuVO4 lasers operated at 916 nm and 458 nm for the first time. The maximum output power of 780 mW at 916 nm laser is obtained with a slope efficiency of 9.3%. We generate 50 mW of 458 nm blue laser employing a type-I critical phase-matched LBO crystal.

We realize a stable self-starting passively mode-locking all-solid-state laser by using novel GaAs mirrors as the absorber and output coupler. The GaAs mirror is grown by the technology of metal organic chemical vapour deposition at low temperature. With such an absorber as the output coupler in the laser resonator, laser pulses with duration of 42ps were generated at a repetition rate of 400MHz, corresponding to the average power of 590mW.

Strong white light emission is observed from femtosecond laser propagation in air. The divergence angle of the white light emission is measured to be about 5 mrad. Young's double-slits and a Michelson interferometer are used to investigate the coherence. The wavelength components of the white light emission are identified to have a good spatial coherence and a coherence time of about 0.5 ps.

We demonstrate a diode-pumped passive Q-switched 946 nm Nd:YAG laser with a diffusion-bonded composite laser rod and a co-doped Nd,Cr:YAG as saturable absorber. The average output power of 2.1 W is generated at an incident pump power of 14.3 W. The peak power of the Q-switched pulse is 643 W with 80 kHz repetition rate and 40.8 ns pulse width. The slope efficiency and optical conversion efficiency are 17.6% and 14.7%, respectively.

By using a semiconductor saturable-absorber output coupler as a mode-locking device, we experimentally realized the operation of a diode-pumped passively mode-locked Nd:YVO4 laser. Stable laser pulses with duration of 2.3 ps were generated at the output power of about 1 W. With increasing the pump power to 9 W, the maximum mode-locked power of 1.7 W was obtained, which corresponds to a slope conversion efficiency of 44% and optical-to-optical conversion efficiency of 19%.

We demonstrate a widely tunable near-infrared source from 767 nm to 874 nm generated by the intracavity second harmonic generation (SHG) in an optical parametric oscillator pumped by a Yb:LYSO solid-state laser. The home-made Yb:LYSO oscillator centered at 1035 nm delivers an average power of 2 W and a pulse duration as short as 351 fs. Two MgO doped periodically poled lithium niobates (MgO:PPLN) with grating periods of 28.5–31.5 μm in steps of 0.5 μm and 19.5–21.3 μm in steps of 0.2 μm are used for the OPO and intracavity SHG, respectively. The maximum average output power of 180 mW at 798 nm was obtained and the output pulses have pulse duration of 313 fs at 792 nm if a sech2-pulse shape was assumed. In addition, tunable signal femtosecond pulses from 1428 nm to 1763 nm are also realized with the maximum average power of 355 mW at 1628 nm.

A continuous-wave laser oscillation was demonstrated with a Yb-doped fluorapatite (FAP) crystal pumped with a 905 nm Ti:sapphire laser. The output characteristics for different output couplers were investigated. A maximum power of 67mW at a 1043nm wavelength was obtained with 10% output coupler, pumped by a Ti:sapphire laser with 910mW power. This corresponds to a slope efficiency of 26.5%.

The effects of laser polarization on super-hot electron (> 100 keV) generation have been studied in the interaction of femtosecond laser light (800 nm, 150 fs, 6 x 10(15) W(.)cm(-2)) with a pre-formed plasma from a slab Cu target. For p-polarized laser pulses, high-energy gamma -rays of the energy similar to 400keV were detected. The electron temperatures deduced from the gamma -ray spectra were 66 and 52 ke V, respectively, in normal and reflective directions of the solid target, and hot electrons were emitted out of the plasma mainly in the normal direction. In contrast, there were nearly no gamma -rays > 100keV found for s-polarized laser pulses. The hot electron temperature was 26 keV and the emission of hot electrons was parallel to the laser field. The superposition of resonant field with electrostatic field excited by escaping electrons may contribute to the high-energy gamma -ray or super-hot electron (> 100keV) generation.

By observing the fundamental and second harmonic emission from a plasma produced by a 150 fs, 5 mJ laser at 800 nm, the electron temperature, the expansion speed and the scalelength of the plasma have been diagnosed. Moreover the polarization of the fundamental and second harmonic emission has been studied. This could be a useful diagnostic for modulation at the critical surface of the plasma.

In recent years the femtosecond optical frequency combs have led to remarkable advances in metrology optical clocks and attosecond generation etc. In general, the photonics crystal fiber is necessary to broaden the laser spectrum for f-2f method implemented in the traditional femtosecond optical frequency comb. The unavoidable instability introduced by the fiber limits the wide use of the frequency comb. However, owing to obviating the photonics crystal fiber and the interferometer replaced by a single PPLN crystal, the locked state of monolithic frequency comb based on Ti: sapphire laser has been significantly extended, typically from about 1 hour to more than 9 hours. Furthermore, the novel design frequency comb has shown its great potential to reach long-term stabilization as long as more advanced technologies for anti-shock and temperature stabilization can be used. We then test the locked state of the comb by recording f ceo and f rep with universal frequency counters. Besides the long-term locked result, we can also demonstrate that the Allan deviations for the two signals drop as ideal τ+1, respectively. This indicates that the white phase noise is the dominant noise process and then confirms that both f ceo and f rep controlled in experiment are in phase-locked loop. The reproducibility of locked f ceo has been tested by standard statistical method, and the distributions of the locked data are uniform at 95% confidence level.

We report an all-normal-dispersion ytterbium fiber laser mode locked by nonlinear polarization evolution. With a 347-m-long all-fiber ring cavity, a pulse energy of 263 nJ at a repetition rate of 613 kHz is achieved, which is the highest per-pulse energy directly obtained from an all-fiber mode-locked laser doped by ytterbium ions. The compact and operation-robust laser yields a well-shaped spectrum centered at 1032nm with a bandwidth (FWHM) of 4 nm, and the slope efficiency is as high as 27.5%. The proposed low-repetition-rate high-pulse-energy mode-locked fiber laser will be a promising seed for all-fiber chirped pulsed amplification systems.

An all-fiber laser using a single-walled carbon nanotube (SWCNT) as the saturable absorber (SA) for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 mu s to 1.0 mu s, and the highest single pulse energy of 40.6 nJ respectively.

The two-photon spectroscopy of 1S-2S transition in atomic hydrogen needs a narrow linewidth laser at the wavelength of 243 nm. In order to reduce the linewidth to several tens hertz level, a free operation CW ECDL 972 nm laser has been locked to a high fineness ultralow expansion reference cavity by using the Pound-Drever-Hall technique. And the part of 972 nm laser output is set into the tapered amplifier and the two enhanced doubling frequency stages to obtain the output of purple light at 243 nm. It is estimated that such a narrow linewidth laser system at 243 nm can be used well in the detection of the 1S-2S transition of hydrogen.

It is a pivotal step in the measurement of carrier-envelope phase offset frequency in optical femtosecond frequency combs that a stable octave-spanning super-continuum spectrum is generated. In this paper, a home-made Yb:YCOB femtosecond laser pulse is led into a tapered fiber in which some nonlinear effects like self pulse modulation are generated and the four-wave mixing is made to broaden a spectrum to more than one octave-spanning. A Yb:YCOB oscillator emits 130 fs, 620 mW and 76.8 MHz laser pulses, the center wavelength at 1052 nm. Such pulses are focused into a tapered single-mode fiber, and then more than one octave-spanning supercontinuum from 550 nm to 1350 nm has been produced. The coupling efficiency can reach 52% when 323 mW SC laser pulses are detected. Based on the experimental result, a new optical comb will be built with the Yb:YCOB solid state laser as the light source.

A self-starting mode-locked femtosecond laser is accomplished with an oxoborate self-frequency doubling crystal Yb:YCa4O(BO3)3 (Yb:YCOB) as the gain medium and a semiconductor mirror as the saturable absorber. Pumped by a 976-nm fiber-coupled diode laser with 50-μm core diameter, stable mode-locked laser pulses up to 430 mW were obtained at a repetition rate of 83.61 MHz under 5-W pump power. The autocorrelation measurement shows that the pulse duration is as short as 150 fs by assuming the sech2 pulse shape at a central wavelength of 1048 nm. This work has demonstrated a compact and reliable femtosecond laser source for prospective low-cost applications.

The characteristics of high-order harmonic generation (HHG) driven by 5 fs laser pulses interacting with argon under tightly focused geometry are investigated in this paper. By carefully optimizing parameters like dispersion, gas pressure and gas cell position, the enhanced HHG with nearly one order of magnitude in a range of 60-73 eV is observed. Based on single atom approximation and Maxwell propagation equations, numerical simulation is conducted to compare with the experimental characterization with proper parameter. It is proved that the phase-matching plays a crucial role in this phenomenon showing that the theoretical results are in agreement with the experimental results.

We demonstrate a passively cw mode-locked Nd:LuVO4 laser operating on the quasi-three-level at 916 nm with a Z-folded resonator. Using a semiconductor saturable absorber mirror (SESAM) as the passive mode-locking device, we achieve stable cw mode locking with 6.7 ps pulse duration at repetition rate of 133MHz and 88mW average output power under the pump power of 17.1 W.

We report an efficient diode-pumped Nd-doped Gadolinium gallium garnet (GGG) continuous-wave (CW) laser operating at 938 nm. Laser action of 1.6at.% Nd-doped GGG crystals with different lengths and temperatures are also investigated. The maximum output power of 620 mW is obtained at the incident pump power of 5.0 W with a slope efficiency of 15%.

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 report a design of diode-pumped high power Nd:GdVO4/LBO red laser with a compact linear cavity, which can output 820-mW red light at 670 nm with an optical conversion efficiency of 9.6%. The maximum output power of the fundamental light at 1.34 mum was 4 W with a slope efficiency of 45%.

We demonstrate a 100-TW-class femtosecond Tr:sapphire laser running at a repetition rate of 0.1 Hz based on a 20 TW/10 Hz laser facility (XL-II). Pumping the new stage amplifier with a 25J green Nd:glass laser, we successfully improve the laser energy to 3.4 J with duration of 29 fs, corresponding to a peak power of 117 TW.

A real-time ion spectrometer mainly based on a high-resolution Thomson parabola and a plastic scintillator is designed and developed. The spectrometer is calibrated by protons from an electrostatic accelerator. The feasibility and reliability of the diagnostics are demonstrated in laser-driven ion acceleration experiments performed on the XL-II laser facility. The proton spectrum extrapolated from the scintillator data is in excellent agreement with the CR39 spectrum in terms of beam temperature and the cutoff energy. This real-time spectrometer allows an online measurement of the ion spectra in single shot, which enables efficient and statistical studies and applications in high-repetition-rate laser acceleration experiments.

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.

A Gires-Tournois(GT) mirror with a group delay dispersion (GDD) of -60 fs2 in one reflection was designed according to the requirement of dispersion compensation in the Ti-sapphire femtosecond laser system. It was manufactured by ion assisted deposition combined with the optical monitoring in transmission. The reflectance of the mirror was measured by a spectrophometer working in the range from 650 nm to 950 nm with a resolution of 1 nm. The results were consistent with the design. Furthermore, a home-made white light interferometry system was employed to test the reflection GDD and the result also agreed well with the design. The experimental GDD oscillation was less than ± 20 fs2. The GT mirror was applied in the Ti-sapphire femtosecond laser system and a good clamping result was obtained. Finally a 29 fs ultra-short pulse was acquired.

We demonstrate a high-efficiency continuous-wave Tm:YAG ceramic laser pumped with a Ti:sapphire laser. An output power up to 860 mW is obtained under an absorbed pump power of 2.21 W at 785nm, corresponding to a slope efficiency of 42.1% and optical to optical efficiency of 22%. The measured central wavelength is 2012 nm.

We demonstrate the generation of red light femtosecond laser pulses from an intra-cavity frequency-doubled Cr4+ :forsterite laser. An average output power of 75 mW is obtained at the central wavelength of 647 nm with a pulse width of 55 fs by inserting a 500-μm-thick BBO crystal in the laser cavity. The bandwidth of the spectrum of second harmonic pulses is 9 nm, corresponding to a time-bandwidth product of 0.355.

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.

Coherent extreme-ultraviolet (XUV) radiation is studied by interaction of carrier-envelope (CE) phase stabilized high energy 5-fs infrared (800 nm) laser pulses with neon gas at a repetition rate of 1 kHz. A broadband continuum XUV spectrum in the cut-off region is demonstrated when the CE phase is shifted to about zero, rather than modulated spectral harmonics when setting of CE phase is nonzero. The results show the generation of isolated attosecond XUV pulses.

We demonstrate the first quasi-three-level passively Q-switched Nd:GGG laser at 937 nm using a Nd,Cr:YAG crystal as the saturable absorber. The dependences of the average output power, the repetition rate and the pulse width on the incident pump power are obtained. A maximum average output power of 1.18 W with repetition rate of 35 kHz and pulse width of 45 ns is achieved at an incident pump power of 18.3 W. The corresponding optical-to-optical and slope efficiencies are 6% and 10%, respectively.

A Ni-like Mo soft x-ray laser (SXRLs) operating at 18.9nm has been demonstrated by employing a grazing incidence pumping scheme with 120mJ in the 200ps pre-pulse and 140mJ in the 200fs main pulse. The SXRL gain is estimated to be 1.5–3cm−1 when a grazing incidence angle of 14° is applied. Numerical simulations are also performed to investigate the dynamics of the ion distribution. It is found that a high intensity at 2.4 × 1014 W/cm2 of the 200 fs main pulse could heat the pre-plasma rapidly to an appropriate temperature for population inversion, and could compensate for the shortage of the total pump energy to a certain extent.

A novel method is developed to obtain 1.05 μm laser operation with a Yb:YAG laser. By using a Yb:YAG crystal with proper length and doping concentration, a femtosecond Yb:YAG laser is realized at the central wavelength of 1053 nm. The measured pulse duration and spectral bandwidth (FWHM) are 170 fs and 7 nm; the repetition rate is 80 MHz. Under a power pump of 2 W, an average mode-locking power of 180 mW is achieved.

A compact femtosecond Ti:sapphire ring oscillator composed of chirped mirrors is designed. By accurately optimizing the intra-cavity dispersion and the mode locking range of the ring configuration, we generate laser pulses as short as 7.7 fs with a repetition rate as high as 745 MHz. The spectrum spans from 660nm to 940nm and the average output power is 480mW under the cw pump laser of 7.5 W.

We demonstrate a 1064nm Nd:YAG laser by directly pumping into the upper lasing level with a tunable Ti:sapphire laser. The valid wavelength is demonstrated at 868.3 nm, 875.2 nm, 883.8 nm, and 885.5 nm, respectively. To our knowledge, this is the first time that 1064 nm Nd:YAG laser pumped by 875.2 nm laser. In addition, laser wavelength at 946 nm is also generated by direct pumping together with traditional pumping.