摘要:

The extensive literature on quantum‐well infrared photodetectors (QWIPs) is reviewed. A detailed discussion is given on the device physics of the intersubband absorption and hot‐carrier transport processes for individual detectors, as well as the high performance which has been achieved for large staring arrays. QWIPs having widely different structures, materials, and spectral responses are covered, as is the optimization of the quantum‐well parameters for maximum performance.  

ISSN:0021-8979    

DOI:10.1063/1.354252

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

One important issue with regard to acceleration of electrons in free space using intense laser beams is the phase slippage of the electrons relative to the electromagnetic field. This arises from a phase velocity mismatch between the electron and light wave. Left uncontrolled this slippage can result in degradation of thee‐beam characteristics (e.g., emittance) and dispersion of the electron bunches. By a method similar to microwave accelerators, multistaging offers a means to control thee‐beam evolution by tuning each successive stage. The phase of the electron bunches relative to the laser field at the entrance of each section determines the acceleration and/or focusing that ensues in that section; therefore, the entrance phase is a natural tuning parameter. It is shown that by controlling the entrance phase it is possible to preserve thee‐beam quality, both transverse (emittance) and longitudinal (bunching, energy spread). Calculations of the longitudinal and transverse beam dynamics are performed to determine the evolution of a finite‐emittanceebeam from stage to stage. By this method the conditions on entrance phase that allow successfule‐beam trapping are found. It is also shown that conditions that assuree‐beam trapping automatically preserve the overall beam quality.

ISSN:0021-8979    

DOI:10.1063/1.354310

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Guided electromagnetic waves in an infinite dielectric plate with general crystal symmetry surrounded by free space are studied in terms of the three‐dimensional Maxwell’s equations. To exhibit as how the crystal symmetry may affect the propagation, symmetry, and coupling of the waves, the study is divided into four cases: (I) &bgr;11,&bgr;22,&bgr;33≠0; (II) &bgr;11,&bgr;22,&bgr;33,&bgr;12≠0; (III) &bgr;11,&bgr;22,&bgr;33,&bgr;23≠0; (IV) all &bgr;ij≠0; where &bgr;ijis the impermeability tensor referred to the rectangular axesxiwith thex2axis normal to the plate faces. Closed‐form solutions are obtained and then the dispersion relations and modes are computed and studied for each case. It is found that in case I, solutions can be separated into the transverse‐electric or TE waves and the transverse‐magnetic or TM waves; TE and TM waves can be further separated into the symmetric and antisymmetric waves. In case II, the solutions for the TE waves remain the same as those in the case I; however, TM waves cannot be separated into symmetric and antisymmetric waves. In case III, solutions cannot be separated into the TE and TM waves, but they can still be separated into the symmetric and antisymmetric waves. In case IV, solutions can neither be separated into the TE and TM waves nor into the symmetric and antisymmetric waves. In case the solutions are not separable, the resulting waves can always be expressed as the sum of symmetric and antisymmetric waves which differ by a phase angle of &pgr;/2. Numerical computations are made for singly and doubly rotated cuts of lithium niobate corresponding to the four cases of symmetry.

ISSN:0021-8979    

DOI:10.1063/1.354311

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A kind of microwave power source, called a free‐electron laser (FEL) afterburner, that consists of a free‐electron laser buncher and a slow‐wave output structure sharing a magnetic wiggler field with the buncher is proposed. The buncher and the slow‐wave structure can operate in either a traveling‐wave state or a standing‐wave state. In the buncher, the wiggler field together with the radiation field makes an electron beam bunched, and in the slow‐wave structure the wiggler field keeps the beam bunched while the bunched beam interacts strongly with the slow‐wave structure and thus produces rf power. The bunching process comes from the free‐electron laser mechanism, and the generating process of rf power is in a slow‐wave structure. A three‐dimensional, time‐dependent code is used to simulate a particular standing‐wave FEL afterburner and it is shown that rf power of up to 1.4 GW at 17.12 GHz, can be obtained from a 1 kA, 5 MeV electron beam with an energy spread of less than 1% and an emittance of less than 0.5×10−3&pgr; rad m.

ISSN:0021-8979    

DOI:10.1063/1.354312

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The electromagnetic field generated by a horizontal electric dipole in the air over a dielectric‐coated conducting or dielectric half‐space is evaluated in an earlier paper subject to the conditionsk20≪k21≪‖k22‖ on the wave numbers of the three regions and the conditionk1l≤ 0.6 on the thicknesslof the dielectric layer. Unintentionally, the severe condition ‖k2 l‖2≪1 was also imposed in the determination of the field in the dielectric layer and the half‐space below it. That restriction is removed in this paper and new complete formulas are derived which have wide potential application.

ISSN:0021-8979    

DOI:10.1063/1.354313

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Measurements are reported of the electro‐optic properties of multiple‐quantum‐wellp‐i‐ndiodes at wavelengths where the waveguide propagation losses are small, 55–110 meV below the exciton resonance. Electroabsorptive and electrorefractive properties were measured as a function of polarization and crystal propagation direction. The electroabsorption and electrorefraction data show that there is a wavelength bandwidth of ∼25 nm where the quadratic electro‐optic coefficient is large (1–7×10−15cm2/V2) and the magnitude of the electroabsorption is <0.5 dB/mm for applied fields of up to 1×105V/cm. Compact, high‐dynamic‐range interferometric modulators can be realized in this wavelength band.

ISSN:0021-8979    

DOI:10.1063/1.354314

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Flat‐top, Ar‐Xe laser pulses at 1.73 &mgr;m have been achieved by pumping the laser medium with a constant‐current electron beam for pulse durations of up to 2.5 ms. The 220 keV electron beam pumped an active volume of 50×8×6 cm3at power loadings of 6–100 W/cm3. Small signal gain, saturation flux, and nonsaturable absorption were determined as a function of Xe concentration, total gas pressure, and pump power density by a Rigrod analysis. In the experimental regime investigated, the small signal gain increased as the total laser pressure decreased and as the partial pressure of Xe decreased. The Xe concentration was varied from 0.5% to 2.0% and the total pressure was varied from 250 to 860 Torr. The results are consistent with Xe quenching of the upper laser level being the dominant deexcitation process and with the collisional broadening dominating the linewidth. The peak intrinsic efficiency observed was 2.2%.

ISSN:0021-8979    

DOI:10.1063/1.354315

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A simple ultraviolet filter utilizing the absorption mechanism of a liquid crystal compound at its isotropic state is demonstrated. Such liquid crystal filter absorbs ultraviolet radiation below the cutoff wavelength and transmits visible and near infrared light with high efficiency. The cutoff wavelength is mainly determined by the liquid crystal material employed, but can be fine‐tuned by varying the absorbing layer thickness. These devices are very simple to fabricate and can be scaled up to large sizes. Practical application for large screen projection display is emphasized.  

ISSN:0021-8979    

DOI:10.1063/1.354316

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Polymeric nonlinear optical waveguides of a copolymer of 4‐(N’‐2‐methacroyloxyethyl‐N‐ methyl‐amino)‐4’‐nitrostilbene and methyl methacrylate were tested for optical power handling capability at near‐infrared wavelengths. When exposed to about 5×105W/cm2optical power density at 1325 nm wavelength laser light, the waveguide showed a rapid decay of optical transmission on the order of about 3 dB/h. Operation of the waveguides in an oxygen‐free environment significantly reduced the decay rate to greater than 0.25 dB/h. The decay was a result of spatially inhomogeneous change of refractive index distributed along the length of the waveguides. Micrographs showing the photoinduced local variations of refractive index and the resulting loss of optical confinement of the waveguides are presented.

ISSN:0021-8979    

DOI:10.1063/1.354317

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

This article describes the demonstration of magneto‐optic channel waveguides in Ce‐substituted yttrium iron garnet which has a very large Faraday rotation. The rib waveguides are successfully produced by employing a new etching technique, which is a reactive ion etching method using BCl3gas. The nonreciprocal phase shift in the magneto‐optic waveguides is measured by using a new improved measurement method. These waveguides exhibit the largest nonreciprocal phase shift ever reported of 21.1 rad/cm (&lgr;=1.55 &mgr;m).

ISSN:0021-8979    

DOI:10.1063/1.354318

出版商:AIP    

年代:1993

数据来源: AIP