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We demonstrate, to the best of our knowledge, the first double-pass pre-chirp managed fiber amplifier. The double-pass fiber amplifier exhibits high gain allowing us to amplify chirped picosecond pulses from 20 mW to 113 W in a rod-type Yb-fiber corresponding to 38 dB gain. We study the dependence of static mode degradation (SMD) on the nonlinear phase shift (NPS) accumulated by the amplified pulse. Our results indicate that a larger nonlinear phase shift results in stronger nonlinear polarization evolution of the fundamental mode and leads to a lower threshold for SMD. After optimization, our pre-chirp managed amplifier seeded by 80 mW pulses delivers 102 W amplified power from the main output. The amplified pulses are compressed to 37 (55) fs with 90 (100) W average power by a grating pair (chirped mirrors). The double-pass configuration significantly simplifies the implementation of pre-chirp managed fiber amplifiers leading to an extremely compact system.

We demonstrate an Yb-fiber based pre-chirp managed amplification system that emits 50-MHz, 47-fs pulses with 101.2-W average power. Using chirped mirrors as a compressor, we achieve 98% throughput efficiency.

OSA continuum 3(7), 1988-1998 (2020). doi:10.1364/OSAC.392981, We incorporate two techniques into pre-chirp managed amplification (PCMA) to achieve high-energy ultrashort pulses with the duration well below 100 fs. Numerical simulations confirmed by our experimental results demonstrate that seeding PCMA with circularly polarized pulses instead of linearly polarized pulses can increase the amplified pulse energy by 1.5 times. We also employ high-dispersion chirped mirrors to compress the amplified pulses with the throughput efficiency as high as 98%. These two techniques allow us to demonstrate an Yb-fiber PCMA system that emits 50-MHz, 47-fs pulses with 101.2-W average power., Published by OSA, Washington, DC

We incorporate circularly polarized seeding pulses and high-dispersion mirror compressor into pre-chirp managed amplification and obtain 50-MHz, 47-fs pulses with 101.2-W average power. The efficiency of the pulse compression is >98%.

Tungsten disulfide (WS 2 ), as one of typical transition metal dichalcogenides with the characteristics of strong nonlinear polarization and wide bandgap, has been widely used in such fields as biology and optoelectronics. With the magnetron sputtering technique, the saturable absorber (SA) is prepared by depositing WS 2 and Au film on the tapered fiber. The heat elimination and damage threshold can be improved for the WS 2 SA with evanescent field interaction. Besides, the Au film is deposited on the surface of the WS 2 film to improve their reliability and avoid being oxidized. The fabricated SA has a modulation depth of 14.79%. With this SA, we obtain a relatively stable mode-locked fiber laser with the pulse duration of 288 fs, the repetition rate of 41.4 MHz and the signal to noise ratio of 58 dB.

We report a high power fiber amplifier based on nonlinear chirped-pulse amplification (NCPA). To manage the nonlinearity, pulse shaping is introduced by self-phase modulation in the fiber stretcher with the help of spectral filtering. The third-order dispersion is compensated for by the nonlinear phase shift in the NCPA. With optimization, the system can output 382 fs pulse duration with 20 W average power at 1 MHz repetition rate. The long-term average power fluctuation is measured to be 0.5% in 24 h, and the beam quality factor (M2) is 1.25.

We demonstrate nonlinear pulse compression of an 8 kHz Nd:YVO4 picosecond laser using the multi-pass-cell (MPC) technique with fused silica as the nonlinear medium. The pulse duration is compressed from 12.5 ps to 601 fs, corresponding to a pulse shortening factor of 20.8. The output pulse energy is 154 µJ with an efficiency of 74.5%. To the best of our knowledge, this is the highest pulse compression ratio achieved in a single-stage MPC with bulk material as the nonlinear medium. The laser power stability and the beam quality (M2) before and after the MPC are also experimentally studied. Both the laser power stability and the beam quality are barely deteriorated by the MPC device.

We report a high power all-normal-dispersion (ANDi) mode-locked laser based on nonlinear polarization evolution (NPE) technique using rod-type fiber with polarization maintaining (PM) characteristic. With 85 μm gain core diameter, 31 W of average power at repetition rates of 57.93 MHz, which corresponds to the pulse energy of 0.53 μJ, is demonstrated under a pump power of 93 W. The pulse duration of 124 fs after compressor is obtained at the central wavelength of 1033 nm as well as the measured power jitter of 0.3% over a period of 2 h.

We utilized a set of fused silica thin plates to broaden the spectrum of 1 kHz, 30 fs Ti:sapphire amplified laser pulses to an octave. Following the compression by chirped mirror pairs, the generated few-cycle pulses were focused onto an argon filled gas cell. We detected high order harmonics corresponding to a train of 209 as pulses, characterized by the reconstruction of attosecond beating by interference of two-photon transition (RABITT) technique. Compared with the conventional attosecond pulse trains, the broad harmonics in such pulse trains cover more energy range, so it is more efficient in studying some typical cases, such as resonances, with frequency resolved RABITT. As the solid thin plates can support high power supercontinuum generation, it is feasible to tailor the spectrum to have different central wavelength and spectral width, which will make the RABITT source work in different applications.

We demonstrate a harmonically pumped femtosecond optical parametric oscillator (OPO) laser using a frequency-doubled mode-locked Yb:KGW laser at a repetition rate of 75.5 MHz as the pump laser. Based on a bismuth borate nonlinear crystal, repetition rates up to 1.13 GHz are realized, which is 15 times that of the pump laser. The signal wavelength is tunable from 700 nm to 887 nm. The maximum power of the signal is 207 mW at the central wavelength of 750 nm and the shortest pulse duration is 117 fs at 780 nm. The beam quality (M2 factor) in the horizontal and vertical directions of the output beam are 1.077 and 1.141, respectively.

We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to 2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation (DFG) in β-barium borate crystal (β-BBO) and passively carrier-envelope-phase (CEP) stabilized. The DFG is induced by few-cycle pulses initiated from spectral broadening in multiple thin plates driven by a Ti: sapphire chirped-pulse amplifier. Furthermore, a numerical simulation is developed to estimate the conversion efficiency and output spectrum of the DFG. Our results show that the pulses from the DFG have the potential for seeding intense mid-infrared (MIR) laser generation and amplification to study strong-field physics and attosecond science.

Severe process margin in advanced technology node of semiconductor device is controlled by e-beam metrology system and e-beam inspection system with scanning electron microscopy (SEM) image. By using SEM, larger area image with higher image quality is required to collect massive amount of data for metrology and to detect defect in a large area for inspection. Although photoresist is the one of the critical process in semiconductor device manufacturing, observing photoresist pattern by SEM image is crucial and troublesome especially in the case of large image. The charging effect by e-beam irradiation on photoresist pattern causes deterioration of image quality, and it affect CD variation on metrology system and causes difficulties to continue defect inspection in a long time for a large area. In this study, we established a quantitative approach for optimizing e-beam condition with “Die to Database” algorithm of NGR3500 on photoresist pattern to minimize charging effect. And we enhanced the performance of measurement and inspection on photoresist pattern by using optimized e-beam condition. NGR3500 is the geometry verification system based on “Die to Database” algorithm which compares SEM image with design data [1]. By comparing SEM image and design data, key performance indicator (KPI) of SEM image such as "Sharpness", "S/N", "Gray level variation in FOV", "Image shift" can be retrieved. These KPIs were analyzed with different e-beam conditions which consist of “Landing Energy”, “Probe Current”, “Scanning Speed” and “Scanning Method”, and the best e-beam condition could be achieved with maximum image quality, maximum scanning speed and minimum image shift. On this quantitative approach of optimizing e-beam condition, we could observe dependency of SEM condition on photoresist charging. By using optimized e-beam condition, measurement could be continued on photoresist pattern over 24 hours stably. KPIs of SEM image proved image quality during measurement and inspection was stabled enough.

In this paper, we demonstrate 67 fs pulse emitting with tungsten disulfide (WS2) in mode-locked erbium-doped fiber (EDF) lasers. Using the pulsed laser deposition method, WS2 is deposited on the surface of the tapered fiber to form the evanescent field. The fiber-taper WS2 saturable absorber (SA) with the large modulation depth is fabricated to support the ultrashort pulse generation. The influences of the WS2 SA are analyzed through contrastive experiments on fiber lasers with or without the WS2 SA. The pulse duration is measured to be 67 fs, which is the shortest pulse duration obtained in the mode-locked fiber lasers with two dimensional (2D) material SAs. Compared to graphene, topological insulator, and other transition metal dichalcogenides (TMDs) SAs, results in this paper indicate that the fiber-taper WS2 SA with large modulation depth is a more promising photonic device in mode-locked fiber lasers with the wide spectrum and ultrashort pulse duration.

We employ high-dispersion chirped mirrors as the pulse compressor and demonstrate an Yb-fiber pre-chirp managed amplification laser system, which produces 55 fs pulses with 43 W average power.

A mode-locked ytterbium fiber laser based on all normal dispersion (ANDi) technique and nonlinear polarization rotation (NPR) is investigated with birefringent plate as a spectral filter in this paper. Tunable triple-wavelength simultaneous operation is realized at central wavelengths of 1031.4, 1046.8 and 1066.5 nm, respectively. A maximum output power up to 161.4 mW is obtained at 1031.4 nm wavelength. By only changing the direction of the optical axis of the uniaxial birefringent filter, tunable range as wide as 19 nm is demonstrated. To the best of our knowledge, this is the widest tuning range and highest power reported so far for ANDi mode-locked ytterbium fiber lasers with triple-wavelength operation. Our analysis shows that the mechanism of the triple-wavelength mode-locked operation results mainly from the four-wave mixing in optical fibers; in addition, the wide gain bandwidth of Yb also plays a critical role for the stable oscillation of the third mode-locked wavelength. The energy conversion process governed by a set of four coupled equations is realized experimentally through the adjustment of the polarization controller, which is related to the phase matching.

We reported the third harmonic generation using a K 3 B 6 O 10 Cl crystal for the first time. Output power of 5.9 mW was obtained at the wavelength of 263-nm, corresponding to conversion efficiency of 4.5% to second harmonic.

Highly-stable, mode-locked, all-polarization-maintaining Yb-fiber laser using nonlinear amplifying loop mirror was demonstrated. The laser delivers 6 nJ pulses in 126 fs, corresponding to saddle-shaped spectrum with 31 nm bandwidth at repetition rate of 8 MHz.

We explored dispersion management of a NPE mode-locked Yb-doped all fiber oscillator by a tapered fiber, the compressed pulse duration of 116fs, power of 36mW, spectrum is widened to near 20nm.

We demonstrated carrier-envelope phase (CEP) stabilized pulse as short as 5.4fs by compressing the octave-spanning spectrum from solid-state plates. Continuous and discrete HHG were observed by using the laser pulse as driver with different CEP.

By inversing the signal and idler in a two-stage noncollinear optical parametric amplifier which is, respectively, pumped by the second harmonic and fundamental wave of femtosecond Ti:sapphire laser at repetition rate of 1 kHz, the carrier-envelope phase (CEP) passively stabilized pulses with a tunable wavelength from 1.1 to 1.6 μm are obtained with maximum energy of 95 μJ at 1.3 μm under the pump energy of 500 μJ. The CEP jitter of pulses is 108 mrad measured by an f-2f interferometer. This work demonstrates a new way to efficiently generate tunable near-infrared femtosecond laser pulses with self-stabilized CEP.

As a saturable absorption material, the heterostructure with the van der Waals structure has been paid much attention in material science. In general, the heterogeneous combination is able to neutralize, or even exceed, the individual material's advantages in some aspects. In this paper, which describes the magnetron sputtering deposition method, the tapered fiber is coated by the MoS2-WS2 heterostructure, and the MoS2-WS2 heterostructure saturable absorber (SA) is fabricated. The modulation depth of the prepared MoS2-WS2 heterostructure SA is measured to be 19.12%. Besides, the theoretical calculations for the band gap and carrier mobility of the MoS2-WS2 heterostructure are provided. By employing the prepared SA, a stable and passively erbium-doped fiber laser is implemented. The generated pulse duration of 154 fs is certified to be the shortest among all fiber lasers based on transition mental dichalcogenides. Results in this paper provide the new direction for the fabrication of ultrafast photon modulation devices.

We propose an approach for producing high-flux isolated-attosecond pulses (IAPs) based on noncollinear geometry of high-order harmonic generation (HHG). By combining a main driving pulse and an ultrashort gating pulse in the interaction medium to form a tilt wave front in a very narrow overlapping time region, the attosecond pulses generated in this region are spatially separated from the original beam in the far field. It gives a way of extracting IAPs as well as fully characterizing an attosecond-pulse train (APT). Since this approach set no restriction on the pulse duration of the main driving pulse, it is particularly suitable for high-flux IAP generation by a high-energy laser which usually has multicycle pulse duration.

A kind of flattened dispersion of large mode hollow-core photonic crystal fiber (HC-PCF) with kagome lattice is proposed. These demonstrate a promising potential in broadening spectrum and pulse post-compressed by using high-power Yb doped fiber or solid laser.

We generated white-continuum covered 450-1000nm with 85% efficiency by injected 25fs Ti:Sapphire laser at 1kHz repetition rate into fused silica pieces. With the 7.1 fs compressed pulses as driver, strong high harmonic generation was observed.

A new approach for producing high flux isolated attosecond pulses (IAP) based on non-collinear geometry was proposed by combining driving and gating pulses, it gives a way of extracting IAP and fully characterizing attosecond pulse.

The accurate Legendre pseudospectral time-domain (PSTD) method is applied in this paper to the study of optical behaviors of 2-D dielectric and plasmonic waveguide-coupled ring resonators. Based on its inherent multidomain scheme with curvilinear-quadrilateral subdomain partitioning, the PSTD method possesses superior advantage in fulfilling field continuity conditions across material interfaces, which provides better numerical handling upon circular or even more complicated ring structures. Accordingly, investigations of several plasmonic nanoring resonators of different shapes with surface plasmon polariton (SPP) waves propagating on the metal/dielectric/metal waveguides are made with the aids of a well-fitted Drude-Lorentz material-dispersion model through analyzing their characteristics in the near-infrared and visible parts of the light spectrum. Especially, the racetrack-shaped ring is carefully designed with optimized track length to avoid the over- or under-coupling problem between the ring and input waveguides and, thus, achieve excellent spectral performance.

Tb 3 Al 5 O 12 transparent ceramics have been prepared by solid state reaction and vacuum sintering. The optical quality and the microstructure of the samples were investigated. The sample sintered at 1650 °C possessed relatively good optical transparency from 400 nm to 1600 nm. The Verdet constant measured at 632.8 nm of the quasi-pore-free Tb 3 Al 5 O 12 transparent ceramic was −172.72 rad T −1 m −1 , which was close to the counterpart of Tb 3 Al 5 O 12 single crystal. The thermal conductivity of the sample was also measured. To the best of our knowledge, this is the first time that Tb 3 Al 5 O 12 transparent ceramic with relatively good optical quality and magneto-optical property has been reported.

A-plane GaN films are deposited on (302) \gamma-LiAlO2 substrates by metalorganic chemical vapor deposition (MOCVD). The X-ray diffraction (XRD) results indicate that the in-plane orientation relationship between GaN and LAO substrates is [010]LAO//[0001]GaN and [203]LAO//[1100]GaN with 0.03% and 2.85% lattice mismatch, respectively. Raman scattering results indicate that the strain in the films decreases along with the increase in the thickness of the films. In addition to the band edge emission at 3.42 eV, defects-related luminescence at 3.35 eV is observed in the photoluminescence (PL) spectra. The cathodoluminescence (CL) spectra indicate that the 3.35-eV emission is related to the V pits.

(Y 0.97− x Zr 0.03 Yb x ) 2 O 3 ( x = 0–0.15) transparent ceramics were fabricated by solid-state reaction. As ZrO 2 was introduced as additive, the transmittance of yttria ceramic was improved greatly. The optical measurements such as absorption, fluorescence spectrum and lifetime of Yb 3+ ion were carried out at room temperature. The intensities of the absorption peaks (904 and 973 nm) increase linearly with Yb 3+ ion concentration. The absorption cross-section at 973 nm and stimulated emission cross-section at 1032 nm are calculated to be 1.175 × 10 −20 and 1.767 × 10 −20 cm 2 , respectively. The lifetime of 5.0 at.% Yb:Y 2 O 3 ceramic is measured to be 0.93 ms. According to the emission spectra and measured lifetime, the optimum doping concentration of Yb 3+ ion in Y 2 O 3 transparent ceramic is in the range of 5.0–8.0 at.%. Meanwhile the up-conversion luminescence is also investigated.

We report a Legendre pseudospectral modeling of silver sphere arrays illuminated by light waves. A special feature of the present computation is that the dispersive nature of silver is described by a Drude-Lorentz model with model parameters obtained by fitting the frequency-domain complex-valued dielectric constants measured experimentally. Numerical validations are conducted based on solving both the near and far fields of the Mie scattering problem, and we observe good convergence on the numerical fields. The far-field patterns of the Ag sphere arrays are simulated. The results are compared to those obtained by the dipole-coupling-model method, and we observe very good agreement between these results. The near-field patterns are also computed, and localized enhanced electric fields in the inter-particle gap regions due to plasmonic coupling between Ag particles are visualized. As the gap between Ag particles is reduced the strength of the localized enhanced electric field is increased.

We demonstrate highly stable mode-locked Yb-doped fiber oscillators using a nonlinear amplifying loop mirror, delivering linearly polarized laser pulses with high energy at a low repetition rate of several MHz. These lasers are composed of polarization-maintaining fibers and fiber-based components without intra-cavity dispersion compensation. The spectral and temporal characteristics are systematically investigated at different repetition rates. Spectral bandwidth of 31 nm is realized in the case of 6 MHz repetition rate, and the pulse energy reaches 10 nJ. A pair of gratings compresses the output pulse to 93 fs. RMS power stability is as low as 0.04% in 10 hours, which shows excellent stability. We believe that this type of fiber oscillator is an ideal seed for further high power amplification.

We implement an ultrafast Yb-doped all-fiber laser which incorporates tapered single-mode fibers for managing nonlinearity and dispersion. The tapered fiber placed in the oscillator cavity aims to broaden the optical spectrum of the intracavity pulse. At the oscillator output, we use another tapered fiber to perform pulse compression. The resulting 66.1-MHz Yb-doped all-fiber oscillator self-starts and generates 0.4-nJ, 65-fs pulses, which can serve as a compact and robust seed source for subsequent high-power, high-energy amplifiers.

The new generation system for ultrahigh-power laser running over Exawatt (EW, 10 18 W) level is emerging recently, which is under a mechanism called Raman backscattering (RBS) in plasma. The main advantage of using plasma is that it can tolerate much higher laser intensities, 10 17 W cm −2 , more than five order of solid-state devices limited, 10 12 W cm −2 . Although Petawatt (PW, 10 15 W) laser pulses have been realized by some groups based on the chirped pulse amplification scheme (CPA), many cutting-edge scientific researches and technical applications, such as inertial confinement fusion (ICF), plasma physics, astrophysics, plasma-based particle accelerators, and X-ray lasers, need even higher laser power than EW level. For these purposes, huge laser projects like the extreme light infrastructure (ELI) have been proposed to offer new paradigm in EW class laser power. However, such an ultrahigh intensity laser system could only be achieved by CPA using very large (beyond 1 m 2 ) and expensive compressor gratings. In addition, to extrapolate CPA to the EW power range, hundreds of such gratings would be required. Even if there is enough budget, the problem of energy restriction on the last grating is still under question. Therefore, it is crucial to find a new medium or new technology for generating femtosecond ultra-intense laser pulses. This paper introduces a solution for generating laser intensities many orders of magnitude higher than currently results. This technology of optical amplification that a process known as Raman backscattering amplification and compression could enable the generation of femtosecond pulses of 20000 times the original seed intensity in a column of plasma just a few millimeters in length and less than a millimeter in width, without stretcher and compressor. Such sufficient high intensity and lower frequency of the pulse amplification indeed have got into super-radiant amplification regime (SRA) or stimulated Raman backscattering (SRBS). It has revealed that an unprecedented large pulse intensity amplification could be realized. The seed pulse will be compressed to 25 fs and its unfocused intensity increased from 1×10 15 to 4×10 17 W cm −2 . Furthermore, it could be increased further to around 1×10 23 W cm −2 by focusing the resulting beam to 1 μm. Therefore, it might be possible to increase this power up to EW in a larger plasma and using more powerful optical pumping.

Materials in the transition metal dichalcogenide family, including WS2, MoS2, WSe2, and MoSe2, etc., have captured a substantial amount of attention due to their remarkable nonlinearities and optoelectronic properties. Compared with WS2 and MoS2, the monolayered MoTe2 owns a smaller direct bandgap of 1.1 eV. It is beneficial for the applications in broadband absorption. In this letter, using the magnetron sputtering technique, MoTe2 is deposited on the surface of the tapered fiber to be assembled into the saturable absorber. We first implement the MoTe2-based Q-switched fiber laser operating at the wavelength of 1559 nm. The minimum pulse duration and signal-to-noise ratio are 677 ns and 63 dB, respectively. Moreover, the output power of 25 mW is impressive compared with previous work. We believe that MoTe2 is a promising 2D material for ultrafast photonic devices in the high-power Q-switched fiber lasers.

ZnO films were fabricated on LiGaO2 (0 0 1), (10 0) and (0 10) planes by RF magnetron sputtering. The structural, morphological and optical properties of as-grown ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectra and photoluminescence (PL) spectra. It is found that the orientation of ZnO films is strongly dependent on the substrate plane. [0 0 0 11, [1 (1) over bar 00] and [11 (2) over bar0] oriented ZnO films are deposited on LiGaO2 (001), (100) and (010), respectively. AFM shows the (0001) ZnO film consists of well-aligned regular hexagonal grains. Raman spectra reveal a tensile stress in the (0 0 0 1) ZnO film and a compressive stress in (110 0) and (112 0) ZnO films. PL spectra of all ZnO films exhibit only a near-band-edge UV emission peak. (C) 2008 Elsevier B.V. All rights reserved.

25 fs pulses with energy up to 0.8 mJ from a multi-pass amplifier system have been spectrally broadened from 460 nm to 950 nm due to strong self-phase modulation (SPM) effect in a gas filled hollow fiber. Using a set of chirped mirrors, the ultra-broadband dispersion compensation was achieved, and the compressed pulses reached their transform limit. Under optimized conditions we achieved pulses with duration of 5.1 fs and with energy of 400 μJ, corresponding to the peak power up to 80 GW.

This paper reports the carrier-envelop phase (CEP) locking for the 5 fs re-compressed laser pulse generated from a chirped pulse amplified (CPA) Ti:sapphire laser at 1 kHz repetition rate. A phase locking feedback system with two loops was designed to control the fast fluctuation arising from the seeding laser and the slow fluctuation arising from the sub-mJ amplified pulse. The principle and structure of the phase control system, including the CEP detection, servo loop design and phase locking result, are analyzed. The experiment shows that our phase locking system can be well used to establish the stable phase locking of few-cycle amplified laser pulse, and the CEP variation of below 53 mrad (rms) was demonstrated during a locking period of more than 3 h.

A mode-locked all-normal-dispersion rod-fiber laser with large core diameter was demonstrated. Output power of 16 W with 270 fs pulse duration is generated. To best knowledge this is the first laser operation with 85 μm core fiber.

Propagation of ultrashort intense laser pulses in a plasma Bragg grating induced by two intersecting laser pulses is studied. Such a plasma grating exhibits an ultrawide photonic bandgap, near which the strong dispersion appears. Particle-in-cell (PIC) simulations show the light speed reduction, pulse stretching, chirped pulse compression, and fast compression of Bragg grating solitons in the plasma grating. The nonlinear coupled-mode theory agrees well with the PIC results. Since the plasma grating can support an ultrahigh damage threshold, it can be a novel photonic device to manipulate extremely intense femtosecond laser pulses.

We have experimentally investigated high-order-harmonic generation driven by a few-cycle truncated Bessel (TB) laser beam which propagates through optical elements of finite aperture sizes. The TB beam was first investigated by Nisoli et al. [Phys. Rev. Lett. 88, 033902 (2002)], who assumed an infinite size for the optical elements so they concluded that the phase and intensity of the laser field oscillate dramatically around the laser focus in space. However, in all real experiments, the optical elements are always finite in size and would further truncate the TB beam, and so the oscillations would dwindle substantially. In this paper we take the finite size of the optical elements into account. We find that the further truncated TB beam has two intensity peaks around the focus. In front of the second peak position the curvatures of the laser phase front and the atomic-dipole phase front have the same absolute values but opposite signs, so the generated harmonic has a flat wavefront and hence a minimized angular divergence. In addition, at this position the pump intensity is not much less than its maximal value. This result is of significant importance in practical applications due to the finite aperture size of all real optical elements.

The plasma jet formed on the rear surface of a foil in laser–solid interaction is investigated by laser probing. The rear plasma jet, which is in line with the laser, formed a few picoseconds after the incidence of the focused laser, is due to a beam of fast electrons propagating through the target and is collimated by a strong magnetic field in the plasma.

We demonstrate efficient generation of continuous spectrum centered at 400 nm from solid thin plates. By frequency doubling of 0.8 mJ, 30 fs Ti:sapphire laser pulses with a BBO crystal, 0.2 mJ, 33 fs laser pulses at 400 nm are generated. Focusing the 400-nm pulses into 7 thin fused silica plates, we obtain 0.15 mJ continuous spectrum covering 350–450 nm. After compressing by 3 pairs of chirped mirrors, 0.12 mJ, 8.6 fs pulses are achieved. To the best of our knowledge, this is the first time that sub-10-fs pulses centered at 400 nm are generated by solid thin plates, which shows that spectral broadening in solid-state materials works not only at 800 nm but also at different wavelengths.

Supercontinuum generation in a solid-state medium was investigated experimentally. A continuum covering 460 to 950 nm was obtained when 0.8 mJ/30 fs Ti:sapphire laser pulses were applied to seven thin fused silica plates at a 1 kHz repetition rate. The primary processes responsible for spectral broadening were self-phase modulation (SPM) and self-steepening, while SPM and self-focusing were balanced to optimize the spectral broadening and suppress the multiphoton process. The output was compressed to a 5.4 fs and a 0.68 mJ pulse, corresponding to two optical cycles and 0.13 TW of peak power.

The free electron density in a 40 mm long filamentation generated by carrier-envelope stabilized few-cycle laser pulses is detected in a circular loop. The oscillation of electron density is observed as a function of CEP.

K3B6O10Cl (KBOC), a new nonlinear optical crystal, shows potential advantages for the generation of deep ultraviolet (UV) light compared with other borate crystals. In this paper we study for the first time the second harmonic generation (SHG) of a femtosecond Ti:sapphire amplifier with this crystal. Laser power is obtained to be as high as 220 mW at the central wavelength of 396 nm with a 1-mm-long crystal, and the maximum SHG conversion efficiency reaches 39.3%. The typical pulse duration is 83 fs. The results show that second harmonic (SH) conversion efficiency has the room to be further improved and that the new nonlinear crystal is very suited to generate the high efficiency deep ultraviolet laser radiation below 266 nm.

Optical diagnostics of evolution of plasmas produced by ultrashort laser pulses is carried out using a femtosecond probing beam. The time sequence of plasma shadowgrams and interferograms are obtained. The filamentation instability in high-density region induces the local density modification. Large-scale toroidal magnetic fields confine plasma expansion in the transverse direction, resulting in the formation of a plasma jet. The plasma expansion along the target normal direction is found to scale as t1/2.

We use a carrier-envelope-phase stabilized sub-2-cycle laser pulse to generate high-order harmonics and study how the two-dimensional spectrum of harmonics, with the resolutions in temporal frequency and spatial frequency, is shaped by the laser phase. An arrowlike spectrum obtained experimentally when the gas cell is located in front of the laser focus point shows a resolution of full quantum trajectories; i.e., harmonics from different trajectories stand on different positions in this spectrum. In particular, due to the laser phase combined with the classical-like action, the harmonics from short and long trajectories differ maximally in their curvatures of wave fronts in the generation area, and so occupy very different ranges of spatial frequency at the far field. The result directly gives a full map of quantum trajectories in high-order harmonic generation. The conclusion is supported by an analytical model and quantum mechanics simulations.

Non-polar m-plane ZnO thin films have been deposited on trenched (named S 1 ) and untrenched (named S 2 ) (100) LiAlO 2 substrates by metal-organic chemical vapor deposition. The full-width at half-maximum (FWHM) value of the X-ray diffraction rocking curve for S 1 is much smaller, compared with that for S 2 . Seen from the frequency shift for the E 2 (high) mode of ZnO in the Raman spectra, S 1 is under a smaller compressive stress than S 2 . Besides, the photoluminescence spectra show that S 1 has a smaller FWHM value (129 meV) for the near band edge emission than S 2 does (137 meV). Polarized Raman spectra and polarized optical transmission spectra show that m-plane ZnO film exhibits optical anisotropy.

Driving laser jitter is one of the main factors affecting the attosecond streaking measurement. The effect of carrier-envelope phase (CEP) jitter and the pulse energy jitter on the attosecond pulse characterization is studied in this paper. We have theoretically calculated and experimentally confirmed that CEP jitter could result in a symmetry trace in the streaking spectrogram, while the intensity jitter could result in a slight shift and broadening of the trace. Both of them can lead to an underestimate of the retrieved attosecond pulse duration.