摘要:

We present a room-temperature study of the well-width-dependent carrier lifetimes in InGaN single-quantum wells. At room temperature, carrier recombination was found to be dominated by interface-related nonradiative processes. The dominant radiative recombination at room temperature was through band-to-band free carriers. For the sample grown at a higher growth rate, we observed a longer luminescence lifetime, which was attributed to an improved quantum well interface. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119568

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Er3+doped aluminosilicate thin films were prepared on silica and silica Si substrates by the sol-gel method. The Er ion concentration was varied from 0.25&percent; to 1&percent;. Fluorescences of Er ions in the visible and infrared regions were characterized. Green and red up-conversion fluorescences centered at 548 and 655 nm for, respectively, the(2H11/2+4S3/2)→4I15/2and2F9/2→4I15/2were observed. A broadband peak was observed at 1531 nm corresponding to the4I13/2→4I15/2transition, with the full width at half-maximum of 47 nm comparable to those prepared by other methods. The fluorescence lifetime of the4I13/2excited state was found to be constant and equal to 3.5 ms until a high Er doping of 0.5 at. &percent;.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119569

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study of electrical conductance of hydrogenated amorphous silicon(a-Si:H) films deposited on optical waveguides in a soda-lime glass (SLG) substrate is carried out, from the viewpoint of electrical instability ofa-Si:H caused by the penetration of Na ions from the glass into the film. The optical waveguides were prepared byK+–Na+orAg+–Na+ion exchange using thermal or field-assisted methods. The effective thickness of optical waveguides was of several micrometers. The obtained results show that in the case ofa-Si:H film deposited on silver waveguide there is a dependence of electrical conductance on measurement duration, if strongly weakened as compared with film deposited on the original SLG substrate. Thea-Si:H films deposited on potassium waveguide and on Na-extracted surface are as stable, as the referent samples with Corning 7059 (Na-free) glass substrate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119570

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An all-optical switch has been proposed based on photoinduced changes of an imaginary part of complex refractive index in a composite thin film made by silver and polymer thin films containing photochromic dye. Very fast switching on and switching off of a reading beam was demonstrated at the incident angle of guided wave mode using a photochromic spiropyran-doped polystyrene thin film and a ns pulsed laser as a writing beam. These responses were caused by the changes of an extinction coefficient due to photochromism. No applied power was required to hold the switched state. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119571

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new way in the fabrication of metallized nano-apertures for near-field optical microscopy is proposed. The method is based on the electrolysis between a silver metallized probe and an electrolytic glass. By dry electrolytic erosion, the metal on the tip apex is removed and lead to a very small metal free aperture. This method applied here to tapered fibers, can be extended to any other metallized tip in a rather reproducible way. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120439

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An electrically pumped three-level system was designed and fabricated using an AlGaAs/GaAs multiple quantum well structure. Under appropriate biases, the structure emits terahertz (THz) radiation, as a result of diagonal (or interwell) intersubband transition. The emission spectra were resolved using an external Fourier transform infrared spectrometer. The center frequency of the emission was voltage tunable. The emission spectra and the power-voltage relation showed clear evidence that the middle level was depopulated by fast longitudinal optical-phonon scattering, thus, a population inversion between the two upper levels is feasible. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119572

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The generation of 200 picosecond pulses of far-infrared radiation from ap-Ge hot hole laser (50–140cm−1) was achieved due to active mode locking by electrical intracavity modulation of the gain. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119573

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report an optically addressed multiple quantum well spatial light modulator with large modulation gain which can be used in applications such as amplified incoherent-to-coherent conversion. The novel device design utilizes separate detector and modulator regions to obtain large gain. The design also incorporates low-temperature-grown quantum wells in the modulator region to reduce the effects of high-intensity readout. Our preliminary data show that modulation gain of 45 and modulation depth of 40&percent; can be obtained by simply applying a dc bias. However, our data also show that the modulation gain decreases at higher writing frequencies, indicating that refreshing the device is required after each write-read operation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119574

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate ultrahigh repetition rate beat signal generation by filtering two modes from the optical spectrum of a 110 GHz pulse train produced by a 1.56 &mgr;m wavelength, subharmonic hybrid mode locked monolithic semiconductor distributed Bragg reflector laser. The beat signal repetition rate can be tuned to any higher harmonic of the 110 GHz frequency up to 1.34 THz. Furthermore, the filtering technique facilitates low phase noise and synchronization with these signals. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119575

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A diffraction grating mounted in the focal region of a modified scanning electron microscope has been used to produce far-infrared Smith–Purcell radiation. The electron beam radius, voltage, and current ranges were 3–27 &mgr;m, 27–40 kV, and 10–140 &mgr;A, respectively. The micron scale of the electron beam was well matched to the evanescent surface waves of the grating. The measured wavelength range extended from 288 to 803 &mgr;m, and both the wavelengths and the intensities observed were in accord with expectations based on theory. The details of the experiment and a summary of the results will be discussed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119576

出版商:AIP    

年代:1997

数据来源: AIP