摘要:

A method for enhancing the efficiency of energy transfer from a relativistic electron beam to an electromagnetic wave in a Cherenkov laser is proposed. In a two‐dimensional Cherenkov laser composed of a planar relativistic electron beam and a parallel plate waveguide loaded with a dielectric grating, either one of the grating parameters, or the slot width and the groove depth, is tapered or gradually decreased in accordance with the decrease in the drift velocity of the electron beam. The numerical simulation demonstrates that sufficient efficiency enhancement can be achieved by a tapered dielectric grating. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116248

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter, we report a quantum well infrared photodetector geometry for normal incidence light coupling. The new optical coupling scheme utilizes total internal reflection at the sidewalls of triangular wires to create favorable optical polarization for infrared absorption. These wires are created by chemically etching an array of V grooves through the detector active region along a specific crystallographic direction. Experimental results from the initial single color as well as two‐color detectors with linear wires and unthinned substrate show efficient light coupling comparable to the standard 45° edge coupling, without the undesirable wavelength dependence or spectral narrowing effect of a conventional grating structure. At the same time, the dark current density is substantially reduced due to the partial material removal. Further improvement is expected by creating a two‐dimensional coupling structure with substrate thinning. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116249

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate a novel approach to phase insensitive, all‐optical steering and switching based on an intensity‐induced change in the propagation direction of multidimensional spatial solitary waves in bulk, birefringent, quadratic nonlinear media. Our demonstration is based on second‐harmonic generation in a KTP crystal. Compensation for the lateral displacements due to walkoff in SHG is observed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116250

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Performance requirements for systems employing optical guided wave components may be satisfied more easily through the hybrid integration of nonlinear optical (NLO) polymers and semiconductors. Reported in this letter, is the integration of NLO polymer waveguides with InGaAsp‐i‐nphotodetectors at 1.3 &mgr;m, with coupling efficiencies greater than 99% and system responsivities of 0.84 A/W. An analysis of the structure using a two‐dimensional beam propagation model was performed. Planarization was maintained and the design allows for further integration of optoelectronic components. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116251

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A mixed‐mode twisted nematic (MTN) liquid crystal cell is developed for both reflective‐mode projection and direct‐view displays. This MTN cell exhibits two times higher brightness and eliminates the parallax problem as commonly observed in reflective displays using a nominal transmissive TN cell. In the meantime, the MTN structure preserves advantageous characteristics of the TN structure such as low operation voltage and high contrast ratio. Confirming computer simulations using Jones matrix method agree with the experimental results well. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116252

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Fine structure has been observed in the 1.4 eV luminescence band of thin (≊100 A˚) amorphous silicon (a‐Si:H) layers deposited on silicon substrates. The energy separation between the peaks is ≊20 meV. A similar luminescence band observed in layers grown on glass substrates under the same conditions is several orders of magnitude lower in intensity and is without perceptible fine structure. There is no change in the nature of the fine structure and the peak energies in films deposited at different substrate temperatures (150–300 °C). The dependence of the luminescence band on illumination intensity and on temperature has also been measured. This indicates probable excitonic nature of the luminescence. Possible causes for the observed phenomena are discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116253

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The critical splay‐to‐bend‐alignment transition in a liquid‐crystal cell treated by parallel rubbing (&pgr; cell) was investigated to improve the optical performance of the display mode using this cell with a compensator. By analyzing the free energy in liquid crystal cells, it was found that nematic media with a smallerK33/K11ratio can reduce the transition voltage considerably, and therefore, also reduce the required optical anisotropy of the liquid‐crystal cell. The significantly improved viewing angle for this mode, achieved by using these newly designed parameters, is also confirmed theoretically and experimentally. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116254

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A hybrid, optoelectronic sampling circuit based on a photoconductive switch and a junction‐field‐effect‐transistor (JFET) source follower/amplifier has been demonstrated to have picosecond response, high‐sensitivity, absolute‐voltage capability, and a very high impedance. The distributed capacitance of the electrical measurement system is reduced to the gate input capacitance of the JFET, and the conventional photoconductive current measurement is transferred into an absolute voltage measurement. Gating measurements with an improvement of 150 times in output voltage over unamplified photoconductive gates have been made using only 10 &mgr;W of average optical power. The effective on‐state resistance of the photogate has also been increased by more than 150 times, indicating that a photoconductive probe with very low invasiveness may be produced. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116255

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have grown Nd:MgO:LiNbO3crystals with periodic ferroelectric domain structures. Absorption and fluorescence spectra measured on these crystals showed little difference from those from Nd:MgO:LibO3with uniform domain structures. Green fluorescence was generated by self‐frequency doubling in a cavity having great losses and pumped by a pulsed dye laser. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116256

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The influence of annealed proton exchanged (APE) waveguides on domain inversion inZ‐cut LiNbO3is reported. For this study, pyrophosphoric acid is used to fabricate planar APE waveguides, both before and after creating domain inversion through the application of an external electric field at room temperature. Domain inversion produced in this manner is shown to sustain the APE process. However, domain inversion is not producible in portions of the substrates having APE waveguides on both crystal faces. The implication of this result for integrated optic device fabrication is discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116257

出版商:AIP    

年代:1996

数据来源: AIP