摘要:

We have investigated intersubband relaxation rates in a stepped quantum well at room temperature using differential transmission spectroscopy with subpicosecond time resolution. The dynamics of the subband populations are derived from the experimentally observed reduction of oscillator strength of the corresponding exciton transitions. In the stepped quantum well the relaxation through longitudinal optical‐phonon emission fromn=3 to 1 (25 ps) is slower than that from 2 to 1 (220 fs), due to the reduced wave function overlap and larger wave vector required for intersubband scattering. When then=3 state is pumped, a population inversion betweenn3 andn2 (which are separated by 7 THz) is observed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116404

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have studied the photoluminescence at 1.5 &mgr;m of the4I13/2→4I15/2transition of the Er3+ion, incorporated as ErF3into polycrystalline YF3, LuF3, and LaF3films, deposited onto SiO2or Si wafers. We conclude that LaF3is an exceptionally suitable host for Er3+, since it permits high Er3+concentrations, long lifetimes of the excited level, and a strong Stark splitting. This results in a spectral shape suitable for broadband optical amplifiers with a usable optical bandwidth exceeding 8000 GHz (&Dgr;&lgr;&bartil;60 nm). ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116405

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Refractive indicesnand absorption coefficients &agr; of epitaxial metastable zincblende structure &bgr;‐GaN(001) were determined over the subband‐gap energy range between 0.8–3.1 eV from an analysis of optical transmission spectra.nwas found to vary from 2.25 to 0.8 eV (1.55 &mgr;m) to 2.50 at 3.1 eV (0.4 &mgr;m) with an energyE(eV) dependence that is well described by a Sellmeir‐type dispersion relationship,n2(E)=1+148/(38.3−E2). The refractive indices of &bgr;‐GaN are 3%–4% smaller than previously reported values for hexagonal &agr;‐GaN. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116406

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

For In0.53Ga0.47As/InP quantum wires fabricated from quantum well material by dry etching and epitaxial regrowth, a blueshift with decreasing wire width is found, where the blueshift is larger than expected by lateral quantization. In magnetophotoluminescence, the quantum well clearly displays a feature that is due to carrier transport between growth islands of different well widths. This feature cannot be observed for small wire structures, which means that the carrier transport is suppressed in these structures. Hence, magnetophotoluminescence measurements give new direct evidence for the fact that the excitons are more and more localized in states of higher energy as the wire width is decreased, which explains the blueshift in the optical spectra. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116407

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of dispersion on the pulsewidth of a mode‐locked fiber ring laser are examined. We have identified two different modes of operation, one where the pulsewidth is determined by the path‐integrated (global) dispersion of the cavity and another novel mode where pulsewidth is not limited by the global dispersion. Experimental results show that for some configurations, the local dispersion of the cavity plays an important role in determining the pulsewidth of the laser. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116408

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Spectral effects arising from linear gain dispersion are shown to strongly influence the ultrafast gain dynamics measured in active semiconductor waveguides using the pump‐and‐probe technique. Measurements on a AlGaAs amplifier under varying amounts of gain dispersion are in good agreement with a simple analytical theory derived from semiclassical density matrix equations. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116409

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe the operation of a high average power, high‐repetition rate, femtosecond optical parametric oscillator in the important 3–5 &mgr;m spectral region. The Ti:sapphire pumped optical parametric oscillator was based on the nonlinear material potassium niobate. The idler wavelength was continuously tunable over the 2.3–5.2 &mgr;m region and average powers as high as 170 mW were measured. At 5.2 &mgr;m, average powers of more than 20 mW were recorded. Idler pulse durations were determined using cross‐correlation techniques and pulses as short as 60 fs were measured in the midinfrared. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116410

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Optical beams are self‐focused and self‐trapped upon initiating crosslinking in photoresists. This nonlinear optical phenomenon is apparent only for low average optical intensities and produces index of refraction changes as large as 0.04. We propose using the self‐focusing and self‐trapping phenomenon in projection photolithography to enhance the resolution and depth of focus. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116411

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The Raman spectra of MoO3implanted with 1, 2, and 4×1016H+/cm2have been recorded at room temperature. It was found that most of the Raman modes ofAgandBgsymmetry, which are observed between 100 and 1100 cm−1, decrease in intensity by the electronic screening of phonons as a result of the electron transfer from hydrogen to Mo. In addition, both Raman modes ofAgsymmetry at 998 and 811 cm−1for MoO3noticeably stiffened at 4×1016H+/cm2, while the orthorhombic structure of MoO3remains unchanged exhibiting no significant change in lattice parameters except for any possible distortion of the MoO6octahedron. The present results are compared with previous studies, in reference to structural information of the hydrogen molybdenum bronzes as well as MoO3. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116412

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A scanning microdeformation microscope based on a vibrating tip with piezoelectric detection in a transmission operating mode is upgraded to operate in reflection mode. Images which reveal subsurface inhomogeneities in silicon and metallic samples are presented. As in the first configuration the lateral resolution and the apparent penetration depth is related to the tip diameter. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116413

出版商:AIP    

年代:1996

数据来源: AIP