摘要:

Nonlinear optical properties of laser‐excited semiconductors are discussed, and the applications to optical bistability and optical logic are reviewed. The physical origin of the nonlinearities is analyzed in terms of the many‐body interactions in the system of electron‐hole pairs, causing effects such as plasma screening of the Coulomb interaction, band‐gap renormalization, and band filling. Theoretical results for absorption and refractive‐index spectra are compared to experimental data obtained for room‐temperature GaAs and other semiconductors. The experimental and theoretical results for dispersive optical bistability in semiconductors are summarized, and recent experiments on optical logic gating and pattern recognition are discussed.

ISSN:0021-8979    

DOI:10.1063/1.340098

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Supposing that an insulator is charged‐up negatively by an accumulation of incident primary electrons, we study how much the subsequent incident electron is influenced by the charge in the specimen. We introduce a new Monte Carlo simulation model of electron scattering in a solid taking into account an electric field around the simulated electron. In a present study the incident electron energy is 20 keV, and the insulator is a poly‐methyl‐methacrylate wafer of 1 mm in thickness. This paper clarifies the changes in some physical quantities, e.g., the backscattering coefficient, energy deposition, etc. due to the specimen charging during an electron beam irradiation.

ISSN:0021-8979    

DOI:10.1063/1.340285

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An infrared optical fiber made of As2S3glass has been applied for remote sensing of hydrocarbon gases. The fiber has enabled a transmission of the radiation at 3.39‐&mgr;m wavelength, where hydrocarbon molecules have strong absorption bands. Using a 3.39‐&mgr;m He‐Ne laser as a light source, an effective remote sensing system has been established. A detection limit of the gas concentration is ∼300 ppm for CH4gas, which is ∼0.6% of the lower explosion limit. The system is also expected as a pressure monitor since it is highly sensitive to the gas pressure.

ISSN:0021-8979    

DOI:10.1063/1.340286

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

X‐ray spectra in the 5–15 A˚ spectral region are presented for various elements with atomic numbers between 9 and 82. Plasma was produced by irradiating plane targets with 1‐J, 800‐ps frequency‐doubled Nd:glass laser pulses at &lgr;=527 nm. The characteristics of the spectra can be varied from pronouncedK‐ andL‐shell line emitters (F to As) to nearly continuous x radiators such as W or Au.

ISSN:0021-8979    

DOI:10.1063/1.340287

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An analytic atomic independent particle model potential adjusted to experimental single‐particle energy levels is used to generate wave functions for the valence and excited states of chlorine. Using these wave functions in conjunction with the Born approximation andLScoupling, we calculate generalized oscillator strengths and integrated cross sections up to 5 keV for various electron impact excitations from the 1s22s22p63s23p5(2P3/2) ground state.

ISSN:0021-8979    

DOI:10.1063/1.340288

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Electromagnetic waves can discriminate between objects of different handedness due to their transverse nature, which implies that the origin of chirality necessarily need not be molecular as in the case of optically active media. By embedding chiral microstructures in a host medium, effectively chiral composites can be constructed. The simplest microstructures are polymer strands which conform to left‐ or right‐handed helices. Using a simple multiple‐scattering theory, the electromagnetic signature of a polymer model, consisting of tiny point‐polarizable spheres strung on helical strands, is examined. From the computed scattered field in the far zone, the equivalent electric and magnetic dipole moments of the helical ensemble are computed for different plane‐wave incidence cases. Based on parametric studies of the equivalent moments, specific recommendations on the helical geometry are made for use in designing chiral composites.

ISSN:0021-8979    

DOI:10.1063/1.340289

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A superradiant and amplified spontaneous transition pulse is obtained from an iodine photodissociation laser amplifier which usesi‐C3F7I as an active molecule and is pumped with a flashlamp (full width at half maximum=3 &mgr;s). We have observed a sharp leading pulse of superradiance whose rise time is less than 50 ns, and the amplified spontaneous emission follows the superradiance during the pumping flash. By measuring the population inversion density in the active medium of the amplifier, we have obtained the threshold condition for the superradiance to take place. Also, the buildup time and peak intensity of the pulse are measured as a function of the flashlamp input energy. By placing a reflecting mirror at a varying distance (from 173 to 673 cm) behind the amplifier, we have found a periodic intensity fluctuation in the superradiance; the period (&Dgr;t) depends linearly on the distance (d), i.e., &Dgr;t=2d/c, wherecis the light velocity.

ISSN:0021-8979    

DOI:10.1063/1.340290

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An optically pumped CO laser that involves a two‐photon excitation of theBstate is described. A photon conversion efficiency of 15% is determined for the 0‐1 and 0‐2 vibraonic transitions of theB‐Asystem. It appears that the major portion of the emitted light is the result of amplified spontaneous emission due to the high gain of the transition.

ISSN:0021-8979    

DOI:10.1063/1.340291

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We present a theoretical analysis of a newly demonstrated semiconductor laser with coupled distributed feedback and Fabry–Perot (DFB‐FP) cavities and show that three modes of operation are possible for such a laser. In mode‐switched DFB mode, the wavelength can be switched between longitudinal modes on either side of the stopband. In coupled‐cavity laser mode, there are successive mode hops inside the stopband. Finally, in continuously tunable distributed Bragg reflector mode, a wide wavelength tuning range (4.8 A˚) without mode hopping can be obtained. The analysis is general enough to be applied to any laser with a periodic waveguide section, and provides an understanding of the mechanisms and the limits of wavelength tuning in such lasers. This type of laser has very important applications in coherent optical communications.

ISSN:0021-8979    

DOI:10.1063/1.340292

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Impulse responses of the piezoelectric photoacoustic (PA) signal have been measured by using the technique of cross correlation. Experimental impulse responses of aluminum model samples are in good agreement with theoretical prediction. It is shown that thermal diffusivities of opaque materials can be determined by measured zero‐crossing times of PA impulse response. Cracks in aluminum samples are detected by measuring a one‐dimensional image of the impulse response of the PA signal.

ISSN:0021-8979    

DOI:10.1063/1.340293

出版商:AIP    

年代:1988

数据来源: AIP