摘要:

We have investigated the compression mechanism of picosecond optical pulses in a far infrared waveguide free electron laser driven by a radio frequency linear accelerator. With a pertinent waveguide gapband the required original phase velocity of the electron bunch, the longitudinal length of a picosecond optical pulse will be continuously shortened so that the pulse power increases quickly until saturation occurs. In order to continue the compression process, an optimal cavity detuning &Dgr;Lcis necessary. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114897

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured current–voltage characteristic, blue‐violet electroluminescence (EL) and subgap photocurrent spectra of free standing polycrystalline chemical vapor deposited diamond film. The current increases as a power law function of the voltage with an exponent of about 5.5. The EL spectra show a main luminescence band peaked at 3.0 eV, whose intensity increases linearly with the electric current. The photocurrent increases rapidly with the photon energy in the range from 2.0 to 3.5 eV and then tends to saturate. It is found that all these results can be consistently explained in relation to gap states centered at 3.0 eV above the valence band. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114898

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Based on plasma dispersion of Si1−xGex, we have fabricated asymmetric 2×2 switches of total internal reflection type, in which Si1−xGexwas grown by molecular beam epitaxy. The optimum intersecting angle is 4°, and the crosstalk is less than −10.6 dB at 76 mA injection current. The insertion loss is 2.8 dB, and the switch time is 0.6 &mgr;s. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114899

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Polarized light emission was observed in conjugated polymer electroluminescent diodes comprising rubbing‐aligned poly(2,5‐dinonyloxy‐1,4‐phenylenevinylene) as the emissive layer. By using 2‐(4‐biphenyly1)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole dispersed in polystyrene as the electron‐transporting/hole‐blocking layer, the electroluminescence efficiency and the dichroic ratio of the electroluminescent light increased, resulting in polarized electroluminescence with a dichroic ratio of 4.0. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114900

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Laser‐induced dark traces in doped LiNbO3crystals are studied with the 1064 nm fundamental radiation and the 532 nm second harmonic radiation of the Nd:YAG laser operating in a pulse mode. The results show that the dark traces are induced only by the 532 nm radiation. The linear relationship between the transmission loss and the 532 nm power density indicates that dark traces are not due to two‐photon absorption. The recovery rates of the absorption in LiNbO3with different wavelength probe laser are measured and show that laser‐induced dark traces accompany more than one defect appearing in LiNbO3, and disappear quicker at higher temperature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114901

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Time‐resolved photoluminescence has been employed to probe the free‐excitonic transitions and their dynamic processes in GaN grown by molecular beam epitaxy (MBE). The exciton photoluminescence spectral line shape, quantum yield, and recombination lifetimes have been measured at different excitation intensities and temperatures, from which the binding energy of an exciton, the energy band gap, and the free‐exciton radiative recombination lifetimes of GaN grown by MBE have been obtained. Our results have demonstrated the superior crystalline quality as well as ultrahigh purity of the investigated sample, implying a new major breakthrough in MBE growth technologies for GaN. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114902

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Highly accurate layer thicknesses are required for multilayers involved in photonic devices, such as Bragg reflectors. In this letter, we demonstrate that precise, real‐time monitoring of molecular beam epitaxy growing layers can be achieved by near‐normal incidence dynamic reflectometry with a tunable sapphire–titanium laser used as a source. The advantage of this new technique lies in the possibility of synchronizing the material changes and the reflectivity extrema by selecting adequate analysis wavelengths. This technique is shown to provide 885 nm GaAs–AlAs Bragg reflectors with a layer thickness accuracy in excess of 1%. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114903

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this letter we report experimental observations of transient UV‐induced frustration of the visible light transmission through Ge‐doped single mode fibers. Fiber side exposure to single nanosecond UV pulses at 266 and 248 nm is found to cause an abrupt decrease in transmission immediately following the pulse and a transmission recovery in microsecond time scale. Transmission changes were monitored at several visible wavelengths and for different types of Ge‐doped single mode fibers. The reported effect occurs independently of the growth and saturation of the permanent UV‐induced absorption reported by other authors. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114904

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have achieved spectrum narrowing to 1 pm in a high‐power ArF excimer laser injection locked by an all solid‐state fourth harmonic (193.4 nm) seed source of 773.6 nm Ti:sapphire laser radiation. Superior laser properties such as sufficient output energy (90 mJ/pulse, 50 pps), locking efficiency exceeding 90%, wavelength drift less than 0.4 pm, and spectrum bandwidth fluctuation less than 0.2 pm were obtained, which meet the requirements for 1 Gbit dynamic random access memory microlithography. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114905

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photonic band gap crystals have been used as a perfectly reflecting substrate for planar dipole antennas in the 12–15 GHz regime. The position, orientation, and driving frequency of the dipole antenna on the photonic band gap crystal surface, have been optimized for antenna performance and directionality. Virtually no radiated power is lost to the photonic crystal resulting in gains and radiation efficiencies larger than antennas on other conventional dielectric substrates. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114906

出版商:AIP    

年代:1995

数据来源: AIP