Single-polarization, dual-wavelength mode-locked Yb-doped fiber laser by a 45°-tilted fiber grating

We experimentally demonstrate an all-fiber single-polarization dual-wavelength Yb-doped fiber laser passively mode-locked with a 45°-tilted fiber grating for the first time. Stable dual-wavelength operation exhibits double-rectangular spectral profile centered at 1033 and 1053 nm, respectively. The 3 dB bandwidth of each rectangular optical spectrum is estimated as 10 nm. The separation of two fundamental repetition rates is 6 kHz. By employing the 45° TFG with the polarization-dependent loss of 33 dB, output pulses with 27 dB polarization extinction ratio are implemented in the experiment. The single pulse centered at 1053 nm is researched by using a filter at the output port of the laser, and the experimental results denote that the output ps pulses are highly chirped. The formation mechanism of dual-wavelength operation is investigated.

Plasma channeling by multiple short-pulse lasers

Channeling by a train of laser pulses into homogeneous and inhomogeneous plasmas is studied using particle-in-cell simulation. When the pulse duration and the interval between the successive pulses are appropriate, the laser pulse train can channel into the plasma deeper than a single long-pulse laser of similar peak intensity and total energy. The increased penetration distance can be attributed to the repeated actions of the ponderomotive force, the continuous between-pulse channel lengthening by the inertially evacuating ions, and the suppression of laser-driven plasma instabilities by the intermittent laser-energy cut-offs.

Attosecond x-ray pulse generation by linear Thomson scattering of intense laser beam with relativistic electron

Linear Thomson scattering of a short pulse laser by relativistic electron lids been investigated using computer simulations. It is shown that scattering of an intense laser pulse of similar to 33 fs full width at half maximum, with an electron of gamma(o) = 10 initial energy, generates an ultrashort, pulsed radiation of 76 attoseconds, with a photon wavelength of 2.5 nm in the backward direction. The scattered radiation generated by a highly relativistic electron has superior quality in terms of its pulse width and angular distribution in comparison to the one generated by lower relativistic energy electron.

Three-dimensional micro- and nano-fabrication in transparent materials by femtosecond laser

Femtosecond pulsed lasers have been widely used for materials microprocessing. Due to their ultrashort pulse width and ultrahigh light intensity, the process is generally characterized by the nonthermal diffusion process. We observed various induced microstructures such as refractive-index-changed structures, color center defects, microvoids and microcracks in transparent materials (e.g., glasses after the femtosecond laser irradiation), and discussed the possible applications of the microstructures in the fabrication of various micro optical devices [e.g., optical waveguides, microgratings, microlenses, fiber attenuators, and three-dimensional (3D) optical memory]. In this paper, we review our recent research developments on single femtosecond-laser-induced nanostructures. We introduce the space-selective valence state manipulation of active ions, precipitation and control of metal nanoparticles and light polarization-dependent permanent nanostructures, and discuss the mechanisms and possible applications of the observed phenomena.

Ta2O5／SiO2硬膜双腔滤光片激光损伤特性研究

研究了Ta2O5／SiO2硬膜双腔干涉滤光片带内、带边及带外的吸收和激光损伤特性。实验发现，对于作用激光，带通滤光片的驻波场分布、吸收率和损伤阈值在带内、带边和带外的响应特性对作用激光波长均呈现出明显的选择性。根据实验结果，结合滤光片的驻波场分析，给出了带通滤光片的损伤机理。

On the percussion drilling of SI using a 20W MOPA based YB fiber laser

A study on the nanosecond fiber laser interaction with silicon was performed experimentally for the generation of percussion drilled holes. Single pulse ablation experiments were carried out on mono crystalline 650μm thick Si wafers. Changes of the mass removal mechanism were investigated by varying laser fluence up to 68 J/cm2 and pulse duration from 50 ns to 200 ns. Hole width and depth were measured and surface morphology were studied using scanning electron microscopy (SEM) and optical interferometric profilometry (Veeco NT3300). High speed photography was also used to examine laser generated plasma expansion rates. The material removal rate was found to be influenced by the pulse energy, full pulse duration and pulse peak power. Single pulse ablation depth of 4.42 μm was achieved using a 200 ns pulse of 13.3 J/cm 2, giving a maximum machining efficiency of 31.86 μm per mJ. Holes drilled with an increased fluence but fixed pulse length were deeper, exhibited low recast, but were less efficient than those produced at a lower fluence. The increased peak power in this case led to high levels of plasma and vapour production. The expansion of which, results in a strong driving recoil force, an increase in the rate and volume of melt ejection, and cleaner hole formation. The experimental findings show that for efficient drilling at a given energy, a longer, lower peak power pulse is more desirable than a high peak power short pulse.

Picosecond laser patterning of PEDOT:PSS thin films

Picosecond pulsed laser (10.4 ps, 1064 nm, 5 and 50 kHz) patterning studies were performed, of PEDOT:PSS thin films of varying thickness deposited by spin coating on glass substrates, by ablating the films or by changing locally by laser irradiation the optical and electrical properties of the polymer. From a detailed observation of the morphology of single pulse ablated holes on the surfaces of the films, in combination with simple calculations, it is concluded that photomechanical ablation is the likely ablation mechanism of the films. The single pulse ablation thresholds were measured equal to 0.13-0.18 J/cm 2 for films with thicknesses in the region of ∼100-600 nm. The implications on ablation line patterning of the films using different fluences, scanning speeds and pulse repetition rates, were investigated systematically. Laser irradiation of the films before ablation induces a metal-insulator transition of the polymer because of the formation of charge localization due to a possible creation of molecular disorder in the polymer and shortening of its conjugation length. © 2010 Elsevier B.V. All rights reserved.

GaAs-based room-temperature continuous-wave 1.59 mu m GaInNAsSb single-quantum-well laser diode grown by molecular-beam epitaxy

Starting from the growth of high-quality 1.3 mu m GaInNAs/GaAs quantum well (QW), the QW emission wavelength has been extended up to 1.55 mu m by a combination of lowering growth rate, using GaNAs barriers and incorporating some amount of Sb. The photoluminescence properties of 1.5 mu m range GaInNAsSb/GaNAs QWs are quite comparable to the 1.3 mu m QWs, revealing positive effect of Sb on improving the optical quality of the QWs. A 1.59 mu m lasing of a GaInNAsSb/GaNAs single-QW laser diode is obtained under continuous current injection at room temperature. The threshold current density is 2.6 kA/cm(2) with as-cleaved facet mirrors. (c) 2005 American Institute of Physics.

12 W high efficiency single frequency ring laser

Single-frequency output power of 12 W at 1064 nm is demonstrated. Pumped by a fiber-coupled diode laser, the Nd:YVO4 produces 58.6% of the slope efficiency with respect to absorbed pump power, and 52.7% of the optical-optical efficiency and nearly diffraction-limited output with a beam quality parameter of M-2 approximate to 1.11. To the best of our knowledge, this is the highest slope efficiency and optical-optical efficiency in single-frequency Nd:YVO4 ring laser. The slope efficiency of the single frequency laser is close to the limit of the efficiency. [GRAPHICS] output spectrum of the single-frequency Nd:YVO4 ring laser

Non-collinear CPOPA seeded by an Yb3+-doped self-starting passive mode-locked fiber laser

Using a home-made seed at 1053 nm from a Yb3+-doped passively mode-locked fiber laser of 1.5 nJ/pulse, 362 ps pulse duration with a repetition rate of 3.842 MHz, a compact, low cost, stable and excellent beam quality non-collinear chirped pulse optical parametric amplifier omitting the bulky pulse stretcher has been demonstrated. A gain higher than 4.0 x 10(6), single pulse energy exceeding 6 mJ with fluctuations less than 2% rms, 14 nm amplified signal spectrum and recompressed pulse duration of 525 fs are achieved. This provides a novel and simple amplification scheme. (c) 2007 Optical Society of America.

Broadly tunable SOA-based active mode-locked fibre ring laser by forward injection optical pulse

We present a broadly tunable active mode- locked. bre ring laser based on a semiconductor optical ampli. er ( SOA), with forward injection optical pulses. The laser can generate pulse sequence with pulsewidth about 12 ps and high output power up to 8.56dBm at 2.5 GHz stably. Incorporated with a wavelength- tunable optical bandpass. lter, the pulse laser can operate with a broad wavelength tunable span up to 37nm with almost constant pulsewidth. A detailed experimental analysis is also carried out to investigate the relationship between the power of the internal cavity and the pulsewidth of the output pulse sequence. The experimental con. guration of the pulse laser is very simple and easy to setup with no polarization- sensitive components.

Passive Q-switching of diode-pumped Yb:YAG microchip laser with ion-implanted GaAs

We reported a passive Q-switched diode laser pumped Yb:YAG microchip laser with an ion-implanted semi-insulating GaAs wafer. The wafer was implanted with 400-keV As^(+) in the concentration of 10^(16) ions/cm^(2). To decrease the non-saturable loss, we annealed the ion-implanted GaAs at 500 oC for 5 minutes and coated both sides of the ion-implanted GaAs with antireflection (AR) and highreflection (HR) films, respectively. Using GaAs wafer as an absorber and an output coupler, we obtained 52-ns pulse duration of single pulse.

Passive Q-Switching in a Flash-Lamp Pumped Nd∶YAG Laser with Ion-Implanted GaAs Wafer

A passive Q-switched flash-lamp-pumped Nd:YAG laser with the ion-implanted semi-insulating GaAs water is reported．The wafer is implanted with 400keV As~+ ions in the concentration of 10~(16)cm~(-2). Using GaAs wafer as an absorber and an output coupler．62ns pulse duration of single pulse is obtained.