摘要:

We have obtained efficient laser action from Pr‐doped LaCl3using a novel pumping method. Pump energy is coupled into the crystal through Pr ions in an excited state rather than the ground state. Excited‐state absorption is made possible by a regenerative feedback process (the photon avalanche) utilizing cross relaxation to convert the energy of a single ion in a high‐lying state into energy shared by multiple lower lying state ions.

ISSN:0003-6951    

DOI:10.1063/1.103328

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Self‐defocusing of a Gaussian light beam in a bulk photorefractive BaTiO3crystal is demonstrated. This is a low light intensity process which results from the coupling and power transfer between the spatial frequency components of the beam. We use this effect in photorefractive waveguide structure for all‐optical switching with very low light powers.

ISSN:0003-6951    

DOI:10.1063/1.103329

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report here for the first time, two‐beam coupling energy transfer using the Franz–Keldysh electrorefractive effect in photorefractive semiconductors. A large beam coupling gain coefficient (&Ggr;=2.8 cm−1) exceeding the absorption coefficient (&agr;=2.0 cm−1) is obtained in undoped semi‐insulating GaAs using the new photorefractive process. The new photorefractive process differs from conventional photorefractivity in that the direction of energy transfer is dictated by the direction of an externally applied electric field. Using a moving grating technique and combining the electrorefractive grating with the conventional electro‐optic grating, a very large gain &Ggr;=16.3 cm−1(&agr;=3 cm−1, crystal lengthl=4mm) resulting in net amplification by more than a factor of 200 has been demonstrated.

ISSN:0003-6951    

DOI:10.1063/1.102576

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A dielectric Cherenkov maser has operated as an amplifier at a frequency of 9.8 GHz. The amplifier consisted of an electron beam interacting with the TM01mode of a cylindrical, dielectric lined waveguide with the rf input provided by a tunable (9–10 GHz), 10 kW magnetron. The dielectric constant of the liner was 10 with inner and outer radii of 1.0 and 1.27 cm, respectively. At electron beam voltage and current of 190 kV and 90 A, respectively, the measured power gain of the amplifier was 11 dB over a 21 cm interaction length with a pulse length of approximately 1 &mgr;s.

ISSN:0003-6951    

DOI:10.1063/1.102577

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A multielectrode laser can be used to perform digital logic functions and threshold detection. In addition, the intrinsic gain in these devices allows control of lasing light output without using conventional high‐current electrical switches. Device potential is illustrated by demonstrating logicalandoperation (demultiplexing) at 1.5 Gbit s−1with a bit error rate of <10−11s−1.

ISSN:0003-6951    

DOI:10.1063/1.102578

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Using a novel dynamic etch mask technique and wet chemical etchants, we have produced semiconductor structures with tapered thicknesses, with horizontal slope angles as small as 0.9°. With this technique we have fabricated GaAs/GaAlAs rib optical waveguides in which the etch depth tapered from 0.2 to 1.0 &mgr;m over a distance of 50 &mgr;m, resulting in a 2× change in mode size, with an excess taper loss of less than 0.2 dB. The technique is capable of producing tapers in different orientations, at arbitrary locations on a sample, and appears to be useful for a wide variety of materials systems and devices.

ISSN:0003-6951    

DOI:10.1063/1.102579

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report a new thermal equilibrium behavior in inhomogeneous, undoped amorphous silicon. The room‐temperature conductivity increases by two orders of magnitude compared with the annealed value just after fast cooling from above 180 °C. The decay of the excess conductivity follows (time)−1behavior, which is independent of the temperature. We suggest a possible explanation based on the material inhomogeneity.

ISSN:0003-6951    

DOI:10.1063/1.102580

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A region of anomalous negative capacitance has been observed with forward bias in Se‐Tl Schottky evaporated layer structures. The effect, which is more prevalent in diodes with lower series resistance, is due to an inductive contribution to the impedance that is believed to arise from high‐level injection of minority electrons into the bulk selenium.

ISSN:0003-6951    

DOI:10.1063/1.102581

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Si1−xGexheteroepitaxial layers have been grown on Si(100) surfaces by gas source molecular beam epitaxy. Si2H6and GeH4were used as the Si and Ge source gases, respectively. The Ge mole fractionxin the grown film was found to be controlled by the GeH4flow rate. The growth rate decreased gradually with increasing GeH4flow rate. Selective epitaxial growth of Si1−xGexusing a SiO2mark on a Si(100) substrate was successfully achieved.

ISSN:0003-6951    

DOI:10.1063/1.102582

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A theory is developed for the luminescence linewidth in a quantum well made of ternaries when the two‐dimensionally free excitons undergo alloy disorder scattering. The expression for linewidth shows aL−1dependence on the well widthLfor infinite barrier height. For thin wells leakage of wave function into the barrier is considered. A comparison between the experimental data and the present values points out the dominant role of alloy disorder scattering. For wells thinner than 40 A˚ the calculated values decrease with decreasing well width, indicating the importance of surface roughness scattering.

ISSN:0003-6951    

DOI:10.1063/1.102583

出版商:AIP    

年代:1990

数据来源: AIP