摘要:

This paper reports the experimental and analytical studies of the light amplification of the Fabry–Perot type lasers. Particularly, for high bias current level of the laser amplifier, say more than 90% of the threshold current, the waveform distortion of the amplified output becomes apparent. Considering the following facts that the time division spectra of the input pulse to the amplifier changes from shorter to longer wavelengths due to temperature increase in the active layer after the pulse current is turned on and the peaks of the amplification factors of the Fabry–Perot type amplifiers depend on the wavelength for the different bias current level, we can show that the waveform distortion is caused by the peaks of the spectrum shift of the input and the amplifier. We also observe an important fact that the effective bias current to the amplifier is not the same as the actual bias current, which causes the wavelength shift of the peak gain of the amplifier, because of the reduction of the carrier concentrations in the active layer due to stimulated emission by the input light pulse. Taking into account these facts, the analytical and experimental results are in good agreement with each other.

ISSN:0021-8979    

DOI:10.1063/1.335627

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We present a numerical method for the solution of the cavity modes of a multichannel array of laser diodes. The analysis is based on coupled‐mode theory and includes the appropriate boundary conditions for the electric field at each reflecting facet. Saturable gain is also included, with saturation arising from both the forward‐going and reflected waves. We present results which differ from a recent analytic analysis for the case of two channels with different gains and propagation constants. The present work predicts ‘‘cavity supermodes’’ which are similar to the ‘‘symmetric’’ and ‘‘antisymmetric’’ waveguide supermodes previously described in the literature. These cavity modes are characterized by equal intensities in both channels even when the channel gains are grossly different.

ISSN:0021-8979    

DOI:10.1063/1.335628

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Photoluminescence and absorption data are presented on AlxGa1−xAs‐GaAs superlattices (SLs) disordered into bulk‐crystal AlyGa1−yAs (0≤y≤x) by Si or Ge diffusion. The bulk‐crystal AlyGa1−yAs produced by impurity‐induced disordering (by Al‐Ga interchange) is determined by transmission electron microscopy, absorption measurements, and photoluminescence to be homogeneous, with an alloy composition (y) that agrees with the average Al concentration of the SL. For low enough Al concentration (y≊0.23<yc=0.44, the direct‐indirect crossover), in absorption the Ge‐ or Si‐disordered SL exhibits (4.2 and 77 K) the bulk‐crystal exciton, which is characteristic of homogeneous alloy (AlyGa1−yAs). Stimulated emission (4.2 and 77 K) in bulk‐crystal AlyGa1−yAs is observed &Dgr;E≤50 meV below the band edge via photopumping for both Si‐ and Ge‐disordered SLs of Al concentration yieldingy∼0.23 andy∼0.39. Shallow hydrogenlike donor or acceptor states are characteristic of AlxGa1−xAs‐GaAs SLs disordered with Ge or with Si. For the Si impurity (i.e., an AlxGa1−xAs‐GaAs SL disordered with Si), however, much deeper states (transitions) are observed that saturate at higher photoexcitation levels. These states are attributed to nearest‐neighbor or extended Si‐Si pairs since similarly disordered AlxGa1−xAs‐GaAs SLs doped with Ge do not exhibit deeper states.

ISSN:0021-8979    

DOI:10.1063/1.335710

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

This paper analyzes the static stability of a mercury droplet held in a geometry consisting of two parallel gaps connected by a short tube. This arrangement finds application as a high‐efficiency optical modulator which works in reflection, with the mercury surface acting as a mirror. Theoretical calculations of the pressure balance and the system energy are presented which lead to conclusions concerning the design of these devices.

ISSN:0021-8979    

DOI:10.1063/1.335711

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Design and operation of a cw, transverse‐flow oxygen‐iodine chemical laser are reported. Reactant recirculation in the O2(1&Dgr;) chemical generator allows long duration (up to 2 h) operation. Peak powers of 460 W, and stable outputs of 80 W have been demonstrated. Power extraction efficiencies of up to 65% were measured for 80‐W operation, and the implications of this observation for theI2dissociation mechanism are discussed.

ISSN:0021-8979    

DOI:10.1063/1.336293

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The optoacoustic generation and electrical detection of acoustic pulses of about 0.5‐ns duration in quartz and in several polymer materials is demonstrated. The ultrasonic pulses are generated by thermoelastic effects and/or ablation due to absorption of 70‐ps laser‐light pulses in an opaque coupling layer deposited on one of the sample surfaces. Detection of the acoustic pulses is possible by using electrically charged, piezoelectric, or biased samples which yield electrode signals upon transit of the pulses. The acoustic pulses have also have been used to measure ultrasonic velocity and attenuation in various materials.

ISSN:0021-8979    

DOI:10.1063/1.335712

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In this paper we describe a new technique, based on Fourier optics, to explain the propagation, as well as loss, of three‐dimensional thermal waves in isotropic, homogeneous materials. Using this, the dependence of temperature distribution at any arbitrary infinite parallel plane on the aperture distribution is derived. In addition, the temperature distribution at the aperture plane, due to a given perpendicular source is formulated, by applying the boundary conditions in the spatial frequency domain. A scattering matrix theory is developed to analyze the propagation of thermal waves in multilayered structures. This directly relates the heat source characteristics to the temperature distribution at any level. The contrast mechanism in the subsurface mode of operation is explained, and the dependence of the response of a typical system on depth is explored. In addition, the theoretical amplitude and phase images of a cylindrical void are presented; the results are in good agreement with the published experimental subsurface images of voids. Finally, transform techniques in both temporal and spatial frequency domains are employed to analyze the pulse response of layered structures. It is found that the decay rate of the surface temperature is strongly influenced by the presence of inclusions within a sample.

ISSN:0021-8979    

DOI:10.1063/1.335713

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Desorbed gases from insulator surfaces may be much more important in flashover initiation than properties of the dielectric surface. Ambient neutral densities, immediately above the insulator surface, in the initial stages of flashover have been calculated to lie in the range from 2×1017/cm3to 2×1021/cm3with a mean of about 1×1019/cm3, whether flashover occurred on surfaces in air at atmospheric pressure or in vacuum as low as 10−6Torr. The evidence presented indicates that, for dc and microsecond pulse voltages, surface flashover is a local, relatively high‐pressure phenomenon. Comparison of field strengths of surface flashover for various insulating materials perpendicular to the electrodes, operating pressures, and voltage waveforms appears to indicate that flashover values range well within an order of magnitude (∼18–80kV/cm). A filamentary nature of the flashover discharge is shown and is consistent with gas breakdown phenomena. Ionization wave front velocities are examined and these compare favorably with those obtained from gaseous breakdown studies.

ISSN:0021-8979    

DOI:10.1063/1.335698

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The output performance of two thermionic energy converters is compared. One converter has a normal emitter, working with zero field at the emitter which is close to the optimum working point, and the other has a low work function emitter and ion reflection at the emitter. A simple model of the plasma and the sheaths shows that a converter working with a low work function emitter and ion reflections gives a worse performance than a similar converter with a normal emitter.

ISSN:0021-8979    

DOI:10.1063/1.335699

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The surface flashover of Teflon, plexiglass, quartz, Pyrex glass, Macor glass‐ceramic, and sapphire solid insulators has been measured in vacuum (∼10−8Torr, ∼10−6Pa) and in atmospheric air using dc, ac (60 Hz), and 1.2/50‐&mgr;sec lightning impulse voltages. The dependence of the flashover voltage on the following parameters is investigated: (1) spacer material, (2) diameter of the spacer, (3) spacer length, (4) number of spacers stacked in series, (5) air pressure in the range 10−6–105Pa, (6) electrode material, (7) spark conditioning, and (8) the external resistance in series with the gap. At a fixed insulator length the flashover voltage decreases with increasing spacer diameter. The withstand voltage of spacers stacked in series increases with increasing the number of spacers. The dc flashover voltage of different insulating materials is theoretically calculated in vacuum as a function of the length of the insulator and compared with the experimentally obtained results. Good agreement is obtained.

ISSN:0021-8979    

DOI:10.1063/1.335700

出版商:AIP    

年代:1985

数据来源: AIP