摘要:

We present a method to enhance the energy of the harmonic photon, namely using an additional half-period-delayed pulse. Because of the interference effect of two pulses, the interaction time between the external field and the atomic system is shortened. Thus, the atomic system can sustain a more intense laser pulse. It means that the actual intensity which contributes to harmonic emission will be increased. Therefore, the harmonic is extended to higher order. Our numerical simulations indicate the substantial energy increment of harmonic photons. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118484

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A refractive index grating has been side written in the core of a hydrogen loaded germanosilicate optical fiber using a phase mask and 351 nm light from an Ar ion laser, the longest wavelength yet reported, to the best of our knowledge, for a grating of this type. The grating strength was ∼1.25 dB, indicating an index change of∼2×10−4.The fiber was sensitized by low temperature hydrogen loading followed by a brief exposure to aCO2laser, resulting in the formation of high levels of germanium–oxygen deficiency centers. Fluorescence changes and UV transmission changes in hydrogen loaded germanosilicate glasses exposed to 325 nm and combined 351/364 nm radiation are also reported. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118486

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Off-axis sites for Er have been identified and investigated in congruentLiNbO3by ion-beam/channeling techniques. They do not constitute a different crystalline phase and appear to be associated to clusters or amorphous precipitates. The axial Er ions lie at the Li octahedron but shifted about 0.2 Å from the regular lattice site. Their concentration increases with total Er doping up to saturation level of about 2&percent;. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118487

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Analysis of spontaneous emission spectra of GaInP quantum well laser diodes above and below threshold show that the quasi-Fermi level separation pins within the quantum wells but not throughout the whole device structure. By reproducing the temperature and cavity length dependence of the external differential efficiency using these measurements it is shown that a value of internal differential efficiency which is nonunity is due to current spreading and incomplete carrier injection and that the temperature dependence is due to the temperature dependence of the efficiency with which carriers are injected into the quantum well.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118488

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigate the transient surface emission and the optical gain of cubic GaN on GaAs(001) upon pulsed optical pumping at room temperature. The initial decay time of the transient surface emission drastically decreases with increasing excitation density, reaching a value as short as 20 ps at a fluence of 50 &mgr;J cm−2. This rapid decay suggests the presence of laterally amplified spontaneous emission. In fact, gain-stripe measurements of the edge emission reveal an optical gain exceeding 100cm−1at a fluence of 20 &mgr;J cm−2. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118489

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Deposition of silicon dioxide films on fluorinated amorphous carbon films (a-C:F) for low dielectric constant interlayer dielectrics was investigated. BothSiO2anda-C:F films were deposited by helicon wave plasma enhanced chemical vapor deposition withC4F8fora-C:F andSiH4+O2mixtures forSiO2. TheSiO2films on thea-C:F films peeled off soon after deposition. However, the peeling was suppressed by inserting a thina-C:H buffer layer grown fromCH4between them. The adhesion between the films was increased by making the stoichiometry ofSiO2Si-rich. It was found that the Si–C bonds formed at the interface increased the adhesion. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118490

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

PolycrystallineSrBi2Ta2O9thin films having a layered-perovskite structure were fabricated by a modified metalorganic solution deposition technique using room temperature processed alkoxidecarboxylate precursor solution. It was possible to obtain a complete perovskite phase at an annealing temperature of 650 °C and no pyrochlore phase was observed even up to 600 °C. In addition, theSrBi2Ta2O9thin films annealed at 750 °C exhibited better structural, dielectric, and ferroelectric properties than those reported by previous techniques. The effects of postdeposition annealing on the structural, dielectric, and ferroelectric properties were analyzed. The electrical measurements were conducted onPt/SrBi2Ta2O9/Ptcapacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 330 and 0.023 and the remanent polarization and the coercive field were 8.6&mgr;C/cm2and 23 kV/cm, respectively, for 0.25-&mgr;m-thick films annealed at 750 °C. The leakage current density was lower than10−8A/cm2at an applied electric field of 150 kV/cm. The films showed good switching endurance under bipolar stressing at least up to1010switching cycles. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118485

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The inherent relation between the crystal and magnetic structures for magnetically ordered materials makes it possible to align magnetic particles using magnetic means. The traditionally used static alignment method can only align the particles in one dimension. This report describes dynamic alignment methods which cause the magnetic particles to orient in various patterns according to one’s needs. In particular, particles can be aligned in all three spatial directions thus forming a single-crystallike aggregate of polycrystalline materials. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118491

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ultrahigh vacuum evaporation of magnesium onto a hot silicon substrate (⩾200 °C), with the intention of forming aMg2Sithin film by reaction, does not result in any accumulation of magnesium or its silicide. On the other hand,codeposition of magnesium with silicon at 200 °C, using a magnesium-rich flux ratio, gives a stoichiometricMg2Sifilm which can be grown several hundreds of nm thick. The number of magnesium atoms which condense is equal to twice the number ofsiliconatoms which were deposited; all the silicon condenses while the excess magnesium in the flux desorbs. TheMg2Silayers thus obtained are polycrystalline with a (111) texture. From the surface roughness analysis, a self-affine growth mode with a roughness exponent equal to 1 is deduced. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118492

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the growth of InGaN thick films and InGaN/GaN double heterostructures by molecular beam epitaxy at the substrate temperatures 700–800 °C, which is optimal for the growth of GaN. X-ray diffraction and optical absorption studies show phase separation of InN forInxGal−xNthick films with x>0.3. On the other hand,InxGal−xN/GaNdouble heterostructures show no evidence of phase separation within the detection capabilities of our methods. These observations were accounted for using Stringfellow’s model on phase separation, which gives a critical temperature for miscibility of the GaN–InN system equal to 2457 K.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118493

出版商:AIP    

年代:1997

数据来源: AIP