摘要:

Persistent spectral hole burning was observed at temperatures higher than 77 K inSiO2glass doped with theEu3+ions. TheEu3+-dopedSiO2glass was prepared using the sol-gel process ofSi(OC2H5)4andEuCl3⋅6H2O.A persistent spectral hole was burned in the excitation spectrum of the7F0→5D0transition ofEu3+using a Rhodamine 6G dye laser, of which the hole width and depth were1.6 cm−1and∼20&percent;of the total intensity, respectively, at 77 K. Hole depth decreased with increasing temperature and disappeared above∼130 K.A possible mechanism for the hole burning is related to the local structure aroundEu3+and the residual OH andH2Oin the glass. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120361

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Vertical cavity surface emitting lasers (VCSELs) are demonstrated with reverse-biased tunnel contact junctions allowing low-loss lateral electron current to support hole injection. A compact hybrid vertical cavity is employed consisting of a lower 6.5 periodAlxOy/GaAsdistributed Bragg reflector (DBR) formed by selective oxidation of high Al compositionAlxGa1−xAs,and an electron-beam deposited 5 periodSiO2/Siupper DBR. The cavity (active region) is defined also by selectively oxidizing a current-confining aperture. Lateral electron current drives a tunnel contact junction providing hole injection underneath the upper DBR through the oxide-defined current aperture. Thep-type crystal in the VCSEL is reduced to a minimum, thus reducing resistive loss and device voltage. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120400

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate theoretically that sub-terawatt lasers are capable of producing, through specially arranged cascade processes in optimal targets, substantial amounts of nuclear radiation (positrons, gamma-photons, neutrons, and fission fragments). ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120362

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A method to periodically pole conductive ferroelectric materials has been developed. With this method we have fabricated high quality domain inverted crystals of flux grownKTiOPO4suitable for efficient quasi-phase matched frequency conversion. Samples have been evaluated by second harmonic generation and normalized conversion efficiencies up to6.9&percent;/W cm2have been obtained. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120363

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Intersubband electroluminescence is investigated in structures where two excited states are coupled by tunneling to a common continuum, and exhibit a clear sign of destructive interference in absorption spectroscopy. We show that, in addition to the nonreciprocity between the matrix elements for absorption and emission, the difference between the absorption and emission profiles has its origin also in the electron distribution of the injector. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120364

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

New polyimide type of polymers, aromatic polyimides (APIs) containing sulphur atoms in the backbone, were investigated as electron-hole transporting and light-emitting materials for use in unilayer electroluminescent diodes. The simplicity of synthesis, high thermal stability, organic solvent solubility together with excellent film-forming properties make the APIs potentially of interest for technological applications. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120365

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report a type-II antimonide midinfrared vertical-cavity surface-emitting laser. The emission wavelength of 2.9 &mgr;m is nearly independent of temperature(d&lgr;/dT≈0.07 nm/K)and the multimode linewidth is quite narrow (3.5 nm). The pulsed threshold power at 86 K is as low as 22 mW for a 30 &mgr;m spot. Lasing is observed up toT=280 K,and the peak output power from a 600 &mgr;m spot exceeds 2 W up to 260 K. The differential power conversion efficiency is>1&percent;at 220 K. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120366

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Growth of GaN by rf-plasma molecular beam leads to different surface morphologies for nitrogen-rich growth versus gallium-rich growth. Nitrogen-rich growth produces a significant density of pyramidal hillocks while gallium-rich growth results in flat surfaces. Differences in surface morphology were directly linked to the presence of inversion domains which originated in the nucleation layer. Nitrogen-rich growth and growth under atomic hydrogen enhanced the growth rate of inversion domains with respect to the surrounding matrix, while growth under Ga-rich conditions resulted in a more nearly equal growth rate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120367

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Two types of spiral growth, single and double spirals, ofC60epitaxial films on a KBr(001) substrate were observed by atomic force microscopy (AFM). These single and double spirals were found on films grown at different rates. All spiral islands show the threefold symmetry of the face-centered-cubic (fcc) structure. In the case of single spirals, many fringes were observed in three equivalent [11¯0] directions on the fcc (111) surface. From the AFM images, we concluded that the growth process of these spirals can be explained by the classical crystal growth theory of Burton, Cabrera, and Frank and that screw dislocations form without any direct influence of the substrate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120368

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report results on the direct observation of the microscopic origins of backswitching in ferroelectric thin films. The piezoelectric response generated in the film by a biased atomic force microscope tip was used to obtain static and dynamic piezoelectric images of individual grains in a polycrystalline material. We demonstrate that polarization reversal occurs under no external field (i.e., loss of remanent polarization) via a dispersive continuous-time random walk process, identified by a stretched exponential decay of the remanent polarization. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120369

出版商:AIP    

年代:1997

数据来源: AIP