摘要:

Al‐free 980 nm InGaAs/InGaAsP/InGaP laser structures grown by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) have been optimized for high cw output power by incorporating a broad waveguide design. Increasing the optical‐confinement layer total thickness from 0.2 to 1.0 &mgr;m decreases the internal loss fivefold to 1.0–1.5 cm−1, and doubles the transverse spot size to 0.6 &mgr;m (full width half‐maximum). Consequently, 4‐mm long, 100‐&mgr;m‐aperture devices emit up to 8.1 W front‐facet cw power. cw power conversion efficiencies as high as 59% are obtained from 0.5‐mm long devices. Catastrophic‐optical‐mirror‐damage (COMD) power‐density levels reach 15.0–15.5 MW/cm2, and are found similar to those for InGaAs/AlGaAs facet‐coated diode lasers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117995

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Power extraction from a high‐power soliton fiber ring laser containing a chirped fiber grating is investigated with a variable output coupler. Comparisons are made between the intracavity pulse and the rejection port output pulse. It is shown that a good design for extracting high quality pulses at high power is to insert an intracavity filter to suppress spectral sideband generation and to take the output from the rejection port. The results should apply in general to soliton fiber lasers. Gain saturation is shown to be the main mechanism in the laser that compensates for changes in cavity loss. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117996

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We pump a saturable Bragg reflector (SBR)‐mode‐locked Cr:LiSAF laser with a 0.5 W diffraction‐limited 670 nm laser diode and obtain average CW mode‐locked power of 100 mW of 70 fs pulses at &lgr;=868 nm. The low loss of the SBR‐mode‐locking technique combined with a nearly diffraction limited pumping results in the highest optical conversion efficiency obtained with this type of laser to date. We discuss overall electrical efficiency of femtosecond lasers. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117997

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thin Al2O3films are grown andinsitudoped with erbium by pulsed laser deposition in a single step process, by alternate ablation from Al2O3and Er targets. The as‐deposited films have an Er step dopant profile throughout the film thickness, whose concentration depends on the number of pulses at the Er target. The as‐grown films are optically active, as evidenced by the photoluminescence spectrum centered at 1.533 &mgr;m, corresponding to intra‐4ftransitions in Er3+. The photoluminescence intensity increases upon annealing due to an increase of the luminescence lifetime. This is most likely a result of a decrease in the nonradiative decay channels, related to annealing of defects in the Al2O3film. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117998

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Acoustic waves induced by an intensity modulated focused ion beam have been measured. The experiments were performed with Ga+ions of 35 keV at a current of 3 nA and variable chopping frequency up to 10 MHz in a common focused ion beam system. The acoustic signals were detected by means of a piezoelectric sensor with integrated preamplifier. Frequency and position sensitivity of the sensor has been measured by laser excitation. Ion acoustic measurements have been carried out at the resonance frequencies of the sensor. A dependence on the sample material was found. The results show that the ion acoustic effect can be utilized for imaging and material analysis in focused ion beam systems. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117999

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Results of generation of intense currents of highly charged ions of heavy elements from laser‐produced Au, Pb, and Ta plasmas are reported. High‐power iodine laser PERUN operating with &lgr;=1.315 &mgr;m was used for that purpose. Using a parabolic mirror with a hole in the center instead of a focusing lens increased the efficiency of the illumination system and made the ion measurements along the target normal possible. Multiply charged ions were recorded with an ion energy analyzer in a distance of 240 cm. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117057

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report theoretical and experimental results from research into coaxial extraction of high‐power microwaves fromX‐band traveling wave tube amplifiers. Power levels exceeding 60 MW have been measured at 9.1 GHz. The output level is relatively constant for the full 70 ns duration of the 700 kV, 500 A electron beam pulse. Results indicate that this coaxial geometry is broadband when compared to traditional, highly tuned radial extraction and may thus have applications in a range of high‐power microwave devices. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117058

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The laser induced stimulated emission (LISE) of the Balmer &agr; line is used to measure the ground state hydrogen atom density in an efficient source of hydrogen atoms generated by a low‐pressure (1 Torr), pulsed microwave discharge at 2.45 GHz. The H atom kinetics in pure hydrogen discharges and in hydrogen–air mixture discharges are compared. It is shown that, for high atomic density and long plasma length crossing, the LISE Balmer &agr; line is partially absorbed by the plasma. This provides an estimation of the H(n=2) atom density. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117059

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts onn‐type GaN (∼1017cm−3) epitaxial layers. The metals were deposited either by conventional electron‐beam or thermal evaporation techniques, and then thermally annealed at 900 °C for 30 s in a N2atmosphere. Before metal deposition, the GaN surface was treated by reactive ion etching. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112]TiN//[10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117060

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A complicated behavior was indicated in nanocrystalline Fe78Si9B13alloy with grain size lower than 65 nm. No sign of dislocations after deformation has been found in nanocrystalline material, suggesting that it is unlikely that the dislocation pileup is involved. The reduction of the mean hyperfine field is attributed to a decrease in the number of nearest neighbor atoms on the grain boundaries, which may be responsible for thesofteningbehavior in nanocrystalline material with an average crystallite size of 65 nm. An increasing peak of the phonon mode near 900 cm−1, reflecting strong electron–atom coupling in grain boundary of nanocrystalline material, was observed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117061

出版商:AIP    

年代:1996

数据来源: AIP