Femtosecond laser-induced ZnSe nanowires on the surface of a ZnSe wafer in water

We present a simple route for ZnSe nanowire growth in the ablation crater on a ZnSe crystal surface. The crystal wafer, which was horizontally dipped in pure water, was irradiated by femtosecond laser pulses. No furnace, vacuum chamber or any metal catalyst were used in this experiment. The size of the nanowires is about 1-3 mu m long and 50-150 nm in diameter. The growth rate is 1-3 mu m/s, which is much higher than that achieved with molecular-beam epitaxy and chemical vapor deposition methods. Our discovery reveals a rapid and simple way to grow nanowires on designed micro-patterns, which may have potential applications in microscopic optoelectronics. (C) 2007 Elsevier Ltd. All rights reserved.

Experimental study of the Talbot effect under femtosecond laser illumination

Experimental results of the Talbot effect of an amplitude grating under femtosecond laser illumination are reported. Compared with Talbot image under continuous wave (CW) illumination, Talbot images under femtosecond laser illumination are different due to the wide spectral bandwidth and the Talbot images are more distorted at longer Talbot distances. The spectrums and the pulsewidths of femtosecond laser pulses are measured with the frequency-resolved optical gating (FROG) apparatus. Experimental results are in good agreement with the theoretical analysis. (c) 2005 Elsevier B.V. All rights reserved.

Generation of double pulses in-line by using reflective Dammann gratings

Doubled femtosecond laser pulses in-line are needed in the collinear pump-probe technique, collinear second harmonic generation frequency-resolved optical gating (SHG FROG) and the spectral phase interferometry for direct electric-field reconstruction (SPIDER), etc. Normally, it is generated by using a Michelson's structure. In this paper, we proposed a novel structure with two-layered reflective Dammann gratings and the reflective mirrors to generate doubled femtosecond laser pulses in line without transmission optical elements. Angular dispersion and spectral spatial walk-off are both compensated. In addition, this structure can also compress the positive chirped pulse, which cannot be realized with a Michelson's structure. By adopting triangular grating and blazed gratings, the efficiency of the system would in principle be increased as the Michelson's scheme. Experiments demonstrated that this method should be an alternative approach for generation of the double compressed pulses of femtosecond laser for practical applications. (c) 2006 Elsevier GmbH. All rights reserved.

Talbot effect of a high-density grating under femtosecond laser illumination

The Talbot effect of a high-density grating under femtosecond laser illumination is analyzed with rigorous electromagnetic theory which is based on the Fourier decomposition and the rigorous coupled-wave analysis (RCWA). Numerical simulations show that the contrast of the Talbot images steadily decreases as the transmitted femtosecond laser pulses propagate forward and with wider spectrum width of the femtosecond laser pulses. The Talbot images of high-density gratings have much higher sensitivity of the spectrum widths of the incident laser pulses than those of the traditional low-density gratings. In experiments, the spectrums and the pulse widths of the incident pulses are measured with a frequency-resolved optical grating (FROG) apparatus. The Talbot images are detected by using a Talbot scanning near-field optical microscopy (Talbot-SNOM) technique, which are in coincidence with the numerical simulations. This effect should be useful for developing new femtosecond laser techniques and devices. (C) 2008 Elsevier B.V. All rights reserved.

Radially polarized and pulsed output from passively Q-switched Nd:YAG ceramic microchip laser

For the first time, to the best of our knowledge, a radially polarized laser pulse was produced from a passively Q-switched Nd:YAG ceramic microchip laser with a piece of Cr4+:YAG crystal as the saturable absorber and multilayer concentric subwavelength grating as the polarization-selective output coupler. The averaged laser power reached 450 mW with a slope efficiency of 30.2%. The laser pulse had a maximum peak power of 759 W, a minimum pulse duration of 86 ns, and a 6.7 kHz repetition rate at 3.7 W absorbed pump power. The polarization degree of the radially polarized pulse was measured to be as high as 97.4%. Such a radially polarized laser pulse with a high peak power and a short width is important to numerous applications such as metal cutting. (C) 2008 Optical Society of America

Passively Q-switched Nd:YVO4 laser with a Cr4+:YAG crystal saturable absorber

We demonstrate, for the first time as far as Re known, a passively Q-switched operation of a Nd:YVO4 laser in which a Cr4+:YAG crystal and a laser-diode bar are used as the saturable absorber and the pump source, respectively. Stable laser pulses as short as 28 ns with 20-mu J energy can be generated with this laser, which has the advantages of simplicity, high efficiency, and good long-term stability. (C) 1997 Optical Society of America.

Blue upconversion luminescence generation in Ce3+: Gd2SiO5 crystals by infrared femtosecond laser irradiation

Blue frequency-upconversion fluorescence emission has been observed in Ce3+-doped Gd2SiO5 single crystals, pumped with 120-fs 800 nm IR laser pulses. The observed fluorescence emission peaks at about 440nm is due to 5d -> 4f transition of Ce3+ ions. The intensity dependence of the blue fluorescence emission on the IR excitation laser power obeys the cubic law, demonstrating three-photon absorption process. Analysis suggested that three-photon simultaneous absorption induced population inversion should be the predominant frequency upconversion mechanism. (c) 2006 Optical Society of America.

Thermal, spectroscopic and laser properties of Yb3+Na+: CaF2 single crystals

The effects of Na+ doping level on the thermal conductivities, absorption and emission spectra, and fluorescence lifetimes of Yb3+ ,Na+ :CaF2 crystals were systematically studied. Sites structure, covalent force, and crystal field strength of Yb3+ :CaF2 crystals were markedly varied by codoping Na+ as charge compensator. The 2.0at% Yb3+ and 3.0at% Na+-codoped CaF2 crystal was demonstrated to operate in diode-pumped passively mode-locking scheme. Transform-limited 1 ps laser pulses were obtained, showing the crystal capable of producing ultra-short laser pulses. (c) 2006 Elsevier B.V. All rights reserved.

Formation of arrayed holes on metal foil and metal film by multibeam interfering femtosecond laser beams

We report on an optical interference method to fabricate arrayed holes on metal nickel foil and aluminum film deposited on glass substrate by means of five-beam interference of femtosecond laser pulses. Optical microscope and scanning electron microscope observations revealed that arrayed holes of micrometre-order were fabricated on both metal foil and metal film. The present technique allows one-step, large-area, micrometric processing of metal materials for potential industrial applications.

Optical transfer of periodic microstructures by interfering femtosecond laser beams

We report on an optical interference method for transferring periodic microstructures of metal film from a supporting substrate to a receiving substrate by means of five-beam interference of femtosecond laser pulses. Scanning electron microscopy and optical microscopy revealed microstructures with micrometer-order were transferred to the receiving substrate. In the meanwhile, a negative copy of the transferred structures was induced in the metal film on the supporting substrate. The diffraction characteristics of the transferred structures were also evaluated. The present technique allows one-step realization of functional optoelectronic devices. (C) 2005 Optical Society of America.

Study of crystal formation in titanate glass irradiated by 800 nm femtosecond laser pulse

The structure of the titanate glass is destroyed during irradiation by the femtosecond laser pulses, and (TiO6)(8-) and (TiO4)(4-) anion units are exsolved from the network of the titanate glass. These anion units are rearranged to form some crystals such as anatase and Ba2TiO4 crystals. By Raman spectroscopy, it is found that these crystals have a strong dependence on the intensity of the femtosecond laser pulses. The relation between the generation of these crystals and space distribution of the femtosecond laser power intensity is qualitatively explained. (c) 2005 Elsevier B.V. All rights reserved.

Effect of SiO2 protective layer on the femtosecond laser-induced damage of HfO2/SiO2 multilayer high-reflective coatings

Two kinds of HfO2/SiO2 800 nm high-reflective (HR) coatings, with and without SiO2 protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO2 protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO2 protective layer for HfO2/SiO2 HR coating with SiO2 protective layer. The relation of LIDT for two kinds of HfO2/SiO2 HR coatings in calculation agrees with the experiment result. (c) 2006 Elsevier B.V. All rights reserved.

High repetition rate Q-switched microchip Nd:YVO4 laser with pulse duration as short as 1.1 ns

We have demonstrated a compact and an efficient passively Q-switched microchip Nd:YVO4 laser by using a composite semiconductor absorber as well as an output coupler. The composite semiconductor absorber was composed of an LT (low-temperature grown) In0.25Ga0.75As absorber and a pure GaAs absorber. To our knowledge, it was the first demonstration of the special absorber for Q-switching operation of microchip lasers. Laser pulses with durations of 1.1 ns were generated with a 350 mu m thick laser crystal and the repetition rate of the pulses was as high as 4.6 MHz. The average output power was 120 mW at the pump power of 700 mW. Pulse duration can be varied from 1.1 to 15.7 ns by changing the cavity length from 0.45 to 5 mm. Pulses with duration of 1.67 and 2.41 ns were also obtained with a 0.7 mm, thick laser crystal and a 1 mm thick laser crystal, respectively. (C) 2007 Elsevier GmbH. All rights reserved.

Diode-pumped self-starting mode-locked Nd : YVO4 laser with semiconductor saturable absorber output coupler

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%.

Self-starting passively mode-locking all-solid-state laser with GaAs absorber grown at low temperature

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.