Interaction of ions, electrons, and laser pulses with surfaces

133 p.

Research on a scanner for tilting orthogonal double prisms

The original scanner for tilting orthogonal double prisms is studied to test the tracking performance in intersatellite laser communications. With a reduction ratio of more than 100 times from the change rate of the angle of beam deviation to that of the tilting angle of each prism, the theoretical analysis performed, as well as the verification experiment, indicates that the scanner can meet the requirements of the scanning accuracy superior to 0.5 mu rad with the scanning range greater than 500 mu rad and can facilitate the mechanical structure design. (c) 2006 Optical Society of America.

In situ formation by laser cladding of a TiC composite coating with a gradient distribution

An in situ method was developed to produce an Ni alloy composite coating reinforced by in situ reacted TiC particles with a gradient distribution, using one-step laser cladding with a pre-placed powder mixture on a 5CrMnMo steel substrate. Dispersed and ultra-fine TIC particles were formed in situ in the coating. Most. of the TiC particles, with a marked gradient distribution, were uniformly distributed within interdendritic regions because of the trapping effect of the advancing solid-liquid interface. In addition, the TiC-gamma-Ni interfaces generated in situ were found to be free from any deleterious surface reaction. Finally, the microhardness also showed a gradient variation, with the highest value of 1250 Hv0.2 and the wear properties of the coating were significantly enhanced.

Interactions of a femtosecond intense laser with rare gas clusters in a dense jet\

A study on the interactions of high intensity (similar to 10(16) W/cm(2)) femtosecond laser pulses with rare gas clusters in a dense jet is performed. Energy absorption by Ar and Xe clusters is measured and it can be as high as 90%. Very energetic ions produced in the laser interaction with a dense cluster jet are detected by time-of-flight spectrometry and the maximum ion energy of Xe is up to 1.3 MeV. The average ion energies are found to increase with increasing cluster size and get saturated gradually. The average ion energies also show a strong directionality and the average ion energy in the direction parallel to the laser polarization vector is 40% higher than that perpendicular to it. The findings are discussed in terms of a model of charge-dependent ion acceleration.

Generation of periodic ultrashort electron bunches and strongly asymmetric ion Coulomb explosion in nanometer foils interacting with ultra-intense laser pulse

The interaction of a linearly polarized intense laser pulse with an ultrathin nanometer plasma layer is investigated to understand the physics of the ion acceleration. It is shown by the computer simulation that the plasma response to the laser pulse comprises two steps. First, due to the vxB effect, electrons in the plasma layer are extracted and periodic ultrashort relativistic electron bunches are generated every half of a laser period. Second, strongly asymmetric Coulomb explosion of ions in the foil occurs due to the strong electrostatic charge separation, once the foil is burnt through. Followed by the laser accelerated electron bunch, the ion expansion in the forward direction occurs along the laser beam that is much stronger as compared to the backward direction. (c) 2008 American Institute of Physics.

Temporal-space-transforming pulse-shaping system with a knife-edge apparatus for a high-energy laser facility

For the first time to our knowledge, in a high-energy laser facility with an output energy of 454.37 J, by using a temporal-space-transforming pulse-shaping system with our own design of a knife-edge apparatus, we obtained a quasi-square laser pulse. (c) 2005 Optical Society of America.

110-W fiber laser with homemade double-clad fiber

A high-power ytterbium-doped fiber laser (YDFL) with homemade double-clad fiber (DCF) is introduced in this letter. The geometric parameter and laser characteristics of the fiber have been studied. With one-end-pumping scheme, pumped by a high-power laser diode with launching power of 280 W, a maximum continuous wave (CW) output of 110 W is obtained with an optical-to-optical efficiency of 40%.

Comparison of Yb-doped fiber laser with one-end and double-end pumping configuration

A high-power Ytterbium-doped fiber laser (YDFL) with homemade double clad fiber (DCF) is introduced in this paper. The output power characteristics of a linear cavity fiber laser have been studied theoretically by solving the rate equations and experimentally tested with single- and double-end-pumping configurations. When both ends of the fiber are pumped by two high-power laser diodes with a launched power of similar to 300 W each, a maximum CW output of 444 W is obtained with a slope efficiency of similar to 75%. (c) 2006 Elsevier Ltd. All rights reserved.

Diode-pumped passively q-switched Nd : YAG ceramic laser with a Cr4+: YAG crystal-satiable absorber

Transparent polycrystalline Nd:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3,Y2O3, and Nd2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1750 degrees C in vacuum. Transparent fully dense samples with average grain sizes of 10 mu m were obtained. The 1 at.% Nd:YAG ceramic was used to research passively Q-switched laser output with a Cr4+:YAG crystal as a saturable absorber. An average output power of 94 mW with a pulse width of 50 ns was obtained when the incident pump power was 750 mW. The slope efficiency was 13%. The pulse energy is 5 mu J, and the peak power is about 100 W.

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.

A ridge width varied two-section index-coupled DFB self-pulsation laser with a wide continuously tunable frequency range

A 1.55 mu m InGaAsP-InP index-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. A record wide self-pulsation tuning range above 450 GHz has been achieved for this index-coupled DFB SPL. Furthermore, frequency locking to an optically injected modulated signal is successfully demonstrated.

Blue-violet Lasing of Optically Pumped GaN-Based Vertical Cavity Surface-Emitting Laser With Dielectric Distributed Bragg Reflectors

Optically pumped GaN-based vertical cavity surface-emitting laser (VCSEL) with two Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs) was fabricated via a simplifled procedure direct deposition of the top DBR onto the GaN surface exposed after substrate removal and no use of etching and polishing processes. Blue-violet lasing action was observed at a wavelength of 397.3 ran under optical pumping at room temperature with a threshold pumping energy density of about 71.5 mJ/cm(2). The laser action was further confirmed by a narrow emission linewidth of 0.13 nm and a degree of polarization of about 65%. The result suggests that practical blue-violet GaN-bsaed VCSEL can be realized by optimizing the laser lift-off technique for substrate removal.

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.

InP-based optoelectronic devices for optical fiber communications

In this contribution we report the research and development of 1.55 mu m InGaAsP/InP gain-coupled DFB laser with an improved injection-carrier induced grating and of high performance 1.3 mu m and 1.55 mu m InGaAsP/InP FP and DFB lasers for communications. Long wavelength strained MQW laser diodes with a very low threshold current (7-10 mA) have been fabricated. Low pressure MOVPE technology has been employed for the preparation of the layered structure. A novel gain-coupled DFB laser structure with an improved injection-carrier modulated grating has been proposed and fabricated. The laser structures have been prepared by hybrid growth of MOVPE and LPE techniques and reasonably good characteristics have been achieved for resultant lasers. High performance 1.3 mu m and 1.55 mu m InGaAsP/InP DFB lasers have successfully been developed for CATV and trunk line optical fiber communication.