摘要:

Recently the backscattering of an electromagnetic (EM) missile with an energy decreasing asr−&egr;by a perfectly conducting plate has been studied and the analysis shows that the energy backscattered varies asr−&egr;with the same exponent as the incident EM missile. Scattering of an EM missile by other shapes is left as an open question. In this paper we study the backscattering of an EM missile with energy decreasing asr−&egr;by a perfectly conducting elliptical cylinder. It has been shown that the rate of the energy decay for the backscattered field far from the cylinder is proportional tor−(1+&egr;), which is faster thanr−&egr;for plate scattering but still slower than the ordinary energy decayr−2for a two‐dimensional backscattered field.

ISSN:0021-8979    

DOI:10.1063/1.350309

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We calculate the trajectories of electrons emitted from a sharp protrusion with corners, where the electric field is intense and the radius of curvature tends to zero. The calculations include the effects of a longitudinal magnetic field but ignore the space‐charge effects. We find that the arbitrarily large electric field at a mathematically sharp corner does not necessarily impart to the electrons an excessive amount of transverse momentum, whether or not the external magnetic field is present. Scaling laws are derived for the beam’s transverse displacement in terms of macroscopic quantities, such as anode‐cathode voltage drop, gap separation, magnetic field, and the protrusion dimensions. The implication of these findings on the electron sources generated from microtips is addressed.

ISSN:0021-8979    

DOI:10.1063/1.350259

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have calculated the parameters for an optimal matching layer between a waveguide and a laterally coupled photodetector for TE and TM modes. We find a difference on the order of a few percent between the classical and exact calculations based on optical modes concerning the optimal matching layer thickness. Also, the thickness of the matching layer depends critically on the thickness of the absorbing layer. Comparing TE and TM modes, the absorption maxima for TE(TM) and the minima for TM(TE) coincide approximately, and the maxima and minima depend on the matching layer thickness.

ISSN:0021-8979    

DOI:10.1063/1.350327

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

New symmetrical pi‐conjugated molecules having large third‐order nonlinear susceptibilities, &khgr;(3), are reported. The &khgr;(3)spectra of these molecules have been measured by a THG Maker‐fringe method. The magnitudes of the three‐photon resonant &khgr;(3)reach 10−10esu. The positions of the three‐photon resonance lie at the lowest‐energy peaks in the vibrational structure of each absorption spectra for these molecules.

ISSN:0021-8979    

DOI:10.1063/1.350306

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Transient gratings have been produced in KTa1−xNbxO3by picosecond‐pulse, two‐photon excitation using degenerate four‐wave‐mixing techniques. The excitation process has been characterized through fluorescence studies, and the fluorescence is attributed to the transition between an excited state and the ground state of B4+ions that are produced in ABO3perovskite crystals. Strong electron‐phonon coupling gives rise to the luminescence quenching. The observed degenerate four‐wave‐mixing signal is shown to be due predominantly to a phase grating caused by a change in the susceptibility associated with the formation of Nb4+or Ta4+ions in the peak region of the grating. The grating signal intensity was found to be dependent on the concentration of niobium ions and the crossing angle of the two laser write beams.

ISSN:0021-8979    

DOI:10.1063/1.350312

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Device fabrication and experimental results are reported for a reflectance modulator in which coupling between a 632.8 nm laser beam reflected from the base of a prism and a guided mode in an electro‐optic polymer is electrically varied. The beam intensity was varied ±31% by application of 46 V rms across the polymer. The response is independent of frequency up to at least 5 MHz.

ISSN:0021-8979    

DOI:10.1063/1.350300

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Self‐pumped phase conjugate in trapezoid‐cut Ce‐doped KNa(Sr0.61Ba0.39)0.9Nb2O6crystal was demonstrated without external reflection mirrors and applied field, phase conjugation reflectivities as high as 25% were measured. The threshold power was lower than 0.03 W/cm2. The device operated by one‐region four‐wave mixing using the photorefractive effect.

ISSN:0021-8979    

DOI:10.1063/1.350279

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Experimental results of the temperature dependence of the nonlinear optical response of disperse red 1 and methyl red doped in polystyrene film in the range 90–290 K are reported. It is found that the phase conjugate signal intensity resulting from degenerate four wave mixing is decreased by an order of magnitude at low temperature. The decay time of the recorded grating at fixed pump intensity also decreases with decreasing temperature.

ISSN:0021-8979    

DOI:10.1063/1.350283

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thomson scattering from plasmas in high‐pressure discharges for rare‐gas halide excimer laser pumping was observed using an yttrium‐aluminum‐garnet laser with a second harmonic generator, combined with a double‐monochromator to reject large signal from Rayleigh scattering. The results showed the electron velocity distribution to be Maxwellian which was different from prediction of computer simulations, while variation of electron density and temperature with time and gas composition was consistent with results of computer simulations.

ISSN:0021-8979    

DOI:10.1063/1.350292

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Physical properties of novel grating‐assistedYdirectional couplers are examined using the coupled‐mode theory. A general formalism for the analysis of the lateral perturbed directional coupler properties is presented. Explicit expressions for waveguide key parameters such as coupling length, grating period, and other structural characterizations, are obtained. The influence of other physical properties such as time and frequency response or cutoff conditions are also analyzed. A plane grating‐assisted directional coupler is presented and examined as a basic component in the integrated acoustic technology.

ISSN:0021-8979    

DOI:10.1063/1.350251

出版商:AIP    

年代:1991

数据来源: AIP