摘要:

We propose a method which applies a combination of the well-known phase modulator, butt-couple and prism coupler to the nondestructive measurement of each mode’s propagation loss in multimode waveguides. By tuning to the effective optical length of a channel waveguide with a phase modulator, the contrast in the transmitted intensity of Fabry–Perot resonance for each guided mode separated by a prism coupler can be measured. The associated propagation attenuation coefficient and the propagation loss for each guided mode are then determined from these experimental results. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121733

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We investigate the efficiency of wavelength shifting (generation of a pulse at the wavelength&lgr;p−&Dgr;&lgr;from a signal at&lgr;p+&Dgr;&lgr;under the action of a pump at&lgr;p) and parametric amplification through a cascaded second-order process in a periodically poled lithium niobate crystal. Our results show that, in a 19-mm-long sample, at&lgr;p=1.8 &mgr;mand &Dgr;&lgr; as large as 60 nm, wavelength shifting with unit gain can be obtained with a pump intensity of6 MW/cm2,while amplification by a factor 10 requires18 MW/cm2.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121734

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report efficient room-temperature continuous-wave intracavity frequency doubling of an upconversion-pumpedEr(1&percent;):YLiF4laser at 850 nm. A titanium–sapphire laser was used for excitation of the4S3/2→4I13/2transition in erbium. The maximum laser output power at 850 nm was 1200 mW. Intracavity frequency doubling the fundamental wave utilizing lithium triborate as nonlinear crystal yielded a maximum second-harmonic output power of 540 mW at 425 nm. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121735

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The fabrication and characteristics of organic smart pixels are described. The smart pixel reported in this letter consists of a single organic thin-film field effect transistor (FET) monolithically integrated with an organic light-emitting diode. The FET active material is a regioregular polythiophene. The maximum optical power emitted by the smart pixel is about300 nW/cm2corresponding to a luminance of∼2300 cd/m2.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121736

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A three-dimensional metallodielectric photonic crystal (MDPC) that utilizes planar metal scattering elements in a dielectric medium has been studied in the microwave regime, both experimentally and theoretically. The metal elements are circular copper patches defined on thin dielectric sheets, which are alternately stacked with thicker polyethylene sheets to form a (111)-oriented face-centered-cubic lattice. A photonic stop band has been measured from this “flat-atom” MDPC at 8.4 GHz with a rejection level of 18 dB per lattice period and a width of 50&percent; of the center frequency. Calculations show excellent agreement with measured stop band characteristics, including a similar angular dependence and insensitivity to interplane registration.

ISSN:0003-6951    

DOI:10.1063/1.121737

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have investigated exciton localization inZn1−xCdxSe/ZnSequantum wells by microprobe, spatially resolved luminescence. We found that compositional fluctuations in Cd-rich(x=0.23)quantum wells induce the formation of a tail of states in the gap, where a continuum of localized exciton states forms. On the other hand, shallow quantum wells(x=0.11)exhibit sharp lines due to excitons localized at monolayer well-width fluctuations extending over a few hundred nanometers. The observed results are consistent with the occurrence of localized exciton lasing in deep ZnCdSe quantum wells. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121738

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

First experiments at the Vanderbilt free electron lasers measured the local reflectivity of a PtSi/Si system. The reflectivity in the scanning near-field optical microscope images revealed features that were not present in the corresponding shear-force (topology) images and which were due to localized changes in the bulk properties of the sample. The size of the smallest detected features clearly demonstrated that near-field conditions were reached. The use of different photon wavelengths (0.653, 1.2, and 2.4 &mgr;m) enabled us to probe regions of different depth. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121739

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

With spatially resolved photoluminescence experiments we demonstrate voltage-controlled trapping of excitons in a submicron scale lateral potential superlattice imposed on a semiconductor quantum well. The potential modulation is achieved by two interdigitated field-effect electrodes on top of the sample surface. Both parallel and vertical electric field components strongly modify the optical properties of the quantum well. We show that the lateral modulation of the strength of the quantum confined Stark effect results in an effective lateral exciton potential that can be probed by spatially resolved measurements of the excitonic luminescence. We demonstrate that excitons may be confined to the regions of strongest vertical fields, in which the effective exciton energy is lowest. Spatial resolution of the observed photoluminescence signal allows for a qualitative understanding of the exciton transport and trapping process. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121740

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The upper energy limit of broadly tunable coherent radiation sources based on resonant four-wave mixing is investigated. An argon resonance [the two-photon(3p)54p[5/2](J=2)←(3p)6resonance at10 5617 cm−1]has been used in resonant four-wave mixing to generate tunable coherent narrow-bandwidth extreme ultraviolet radiation. With this resonance, spectroscopically useful laser intensities (up to5×106photons per laser pulse) can be produced beyond 19 eV with a bandwidth as low as0.1 cm−1.The light source is used to record a pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of theb 4&Sgr;g−(v+=1)←X 3&Sgr;g−(v=0)photoelectronic transition ofO2.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121741

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Polymer-dispersed liquid crystal (PDLC) with macroscopically uniaxial molecular alignment containing azobenzene molecules was produced. The PDLC was transparent because of this alignment. Upon photoirradiation to cause trans-cis photoisomerization of azobenzene molecules, the PDLC became translucent even at 30 °C. The PDLC system does not require the use of polarizers and electrodes to fabricate optical devices. The light scattering is ascribed to a biphasic morphology in the system produced transiently by means of the photochemical phase transition. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121742

出版商:AIP    

年代:1998

数据来源: AIP