摘要:

The effects of high pressure up to 24 GPa on carbon nitride were studied usingin situmicro photoluminescence (PL) and infrared (IR) absorption measurements at room temperature. The experiments indicate pressure-induced PL quenching with pressure increasing from 0 to 7 GPa, but the PL remains unchanged from 7 to 24 GPa. The PL results display the pressure effect of PL enhancement after release of pressure to ambient atmosphere. The IR absorption bands broaden toward low frequency after release of pressure. These may be explained by using the PL model of undistorted sp2clusters, which, as PL centers, undergo distortion under pressure and pressure-induced local atomic rearrangement in the sample. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119057

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present experimental results which support a recently proposed scheme for infrared imaging through the combined use of a photon frequency up-conversion device with a charge coupled device (CCD) camera. The epitaxial device consists of a long wavelengthp-type GaAs/AlGaAs quantum well infrared photodetector (QWIP) on top of which is grown a shorter wavelength InGaAs/GaAs light emitting diode (LED). Upon long wavelength infrared excitation of the QWIP, near infrared light is generated by the LED whose output is directed towards a commercial CCD array where the up-converted image of the long wavelength infrared source object is formed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119058

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Experimental and numerical results are presented for a high-frequency oscillator consisting of a resonant-tunneling diode (RTD) series-embedded in a transmission line, one end of which is short circuited and the other end terminated with a load resistor. Like relaxation oscillators, the ac voltage across the RTD is a square wave. However, the current wave form (and hence the load wave forms) consists of a sequence of sharp pulses that are essentially locked to the fundamental mode of the transmission line. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119059

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Luminescence spectra of GaN epitaxial layers grown on sapphire display a strong intensity modulation of the below-band gap transitions and on the low-energy side of the near-band gap transition. The intensity modulation is attributed to a microcavity formed by the semiconductor–air and semiconductor–substrate interface. The microcavity effect is enhanced by using metallic reflectors which increase the cavity finesse. It is shown that microcavity effects can be used to determine the refractive index of the microcavity active material. Using this method, the GaN refractive index is determined and expressed analytically by a Sellmeir fit. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119060

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate a high-quality double-layer antireflection coating for high index (n=2.61at 514 nm) photorefractive and electro-optic bismuth silicon oxide(Bi12SiO20)crystals. The antireflection coating comprises two electron-beam-deposited quarter-wave dielectric layers ofMgF2andZrO2,and increases the beam throughput by as much as 20&percent; per interface at normal incidence. For holographic recording applications, the antireflection coating eliminates multiple internal reflections that produce extraneous gratings. The combination of these two factors significantly increases the diffraction efficiency and the two-beam coupling gain. Key characteristics of the double-layer coating include a broadband minimum that encompasses typical write and read wavelengths forBi12SiO20with normal-incidence reflectivities of less than 0.2&percent; at 514 nm and 1&percent; at 633 nm, respectively, and a forgiving angular dispersion for both TE and TM polarized waves with reflectivities of less than 2&percent; for angles of incidence up to 45°. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119061

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Characteristics of the dc drift phenomenon in electro-optic polymer modulators have been analyzed. It is found that the dc drift originates from the difference between the dielectric relaxation times of the guiding and cladding layers. The dc drift is accelerated as the intensity of the guided light increases. Furthermore, it becomes faster when the device is exposed to visible light. The effect of the guided light and visible light on the dc drift is interpreted in terms of the photoconductivity of the guiding layer. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119062

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

AmorphousSiC/SiO2distributed Bragg reflectors (DBR) deposited by ion beam sputtering at room temperature is reported on in this letter. The DBR consists of only 2.5 pairs and exhibits high peak reflectivity (84&percent;) around ∼1.7 &mgr;m with a full width at half maximum of about 1000 nm. The measured reflectivity spectrum is well reproduced by the equivalent layer theory by using the measured refractive indices of SiC andSiO2and including absorption losses. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119063

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A convenient and fast method to determine the composition of LiNbO3single crystals consisting of a measurement of the position of the fundamental absorption edge in the near UV region is refined and extended to the stoichiometric range. Using unsophisticated apparatus and simple reflection correction, the proposed two-parameter calibration equation provides an absolute accuracy of 0.1 mol &percent; with the relative accuracy reaching an unusual value of better than 0.01 mol &percent; for near stoichiometric compositions. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119056

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate that a quantum well intermixing technique can be used to control the second-order nonlinearity&khgr;zzz(2)in an AlGaAs asymmetric coupled quantum well waveguide structure at 1.52 &mgr;m. Photoluminescence measurements also indicate that the spatial resolution of the impurity-free vacancy disordering process used for quantum well intermixing is better than 1.5 &mgr;m which should be sufficient for first-order quasiphase-matched second harmonic generation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119064

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nanometer-scale Si crystals were produced by selective epitaxial growth on Si(001) surfaces passivated with 0.3-nm-thick oxide films. Window areas for the growth were provided by void formation during the thermal decomposition of the oxide films. Dynamical processes of the void formation and epitaxial growth were observed at 630–730 °C by scanning tunneling microscopy. The crystal shape was a quadrangular pyramid and the typical size was 20 nm in length and 0.8 nm in height. The thin oxide films were found to act as masks for the selective epitaxial growth of nanoscale structures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119065

出版商:AIP    

年代:1997

数据来源: AIP