摘要:

The spontaneous emission spectrum and the small‐signal gain have been measured in a low‐energy, waveguide‐mode free‐electron laser. Measurements are carried out at microwave frequencies (25–40 GHz) in anX‐band rectangular waveguide with a low‐energy (450–600 keV, &ggr;∼2), low‐current (∼1.5 A), low‐energy spread (&Dgr;E/E≪10−4) relativistic photoelectron beam. The measured spontaneous emission spectrum agrees well with the homogeneously broadened spectrum of the TE10waveguide mode. The measured small‐signal gain spectrum is in good agreement with the theoretical prediction calculated under the assumption of operation in the low‐gain Compton regime.

ISSN:0003-6951    

DOI:10.1063/1.102687

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Measurements of the variation of differential gain, refractive index, and linewidth enhancement factor with carrier density in InGaAs‐GaAs strained‐layer quantum well lasers are presented for the first time. These results verify predictions of improvement over unstrained bulk or quantum well lasers, but only at certain carrier densities. Differential gain (dg/dN) is found to vary from 7.0×10−16to 2.5×10−16cm2over the range of carrier densities studied, while the carrier dependence of the real part of the refractive index (dn/dN) ranges from a peak of −2.8×10−20down to −7.0×10−21cm3. From these measurements the resulting linewidth enhancement factor (&agr;) is found to vary from 5 to a minimum of 1.7. This information is critical to successfully exploiting the potential advantages of strained‐layer lasers for such devices as high‐frequency or narrow linewidth lasers.

ISSN:0003-6951    

DOI:10.1063/1.102688

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report the first high quality optical waveguides (loss <1 dB/cm) on alumina and beryllium oxide substrates. The tunability of the polymer guiding layer refractive index is provided through a recently developed wet processing technique. This procedure changes the waveguide propagation loss from larger than 40 dB/cm to less than 1 dB/cm. Since alumina (Al2O3) and beryllium oxide (BeO) are the major substrates for hybrid mode microwave integrated circuits (HMMICs), realization of such waveguides is useful for optical interconnection and signal processing for HMMIC.

ISSN:0003-6951    

DOI:10.1063/1.103313

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Third‐order optical susceptibilities (&khgr;(3)) of poly{(7‐oxo‐7, 10H‐benz[de]imidazo[4’,5’:5,6]benzimidazo [2,1‐a]isoquinoline‐3,4:10,11‐tetrayl)‐carbonyl}, referred to as BBL, and poly(6,9‐dihydro‐6,9‐dioxobisbenzimidazo[2,1b:1’,2’j] benzo[1mn]‐[3,8]phenanthroline‐3,12‐diyl), known as BBB, have been determined using the technique of degenerate four‐wave mixing (DFWM) at 1.064 &mgr;m. BBL has a &khgr;(3)xxxx=(1.5±0.4)×10−11esu, three times as large as that of BBB and 38 times as large as that of CS2. Electrochemical doping led to a small (<30%) increase in the third‐order susceptibility of BBL.

ISSN:0003-6951    

DOI:10.1063/1.102689

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have observed room‐temperature exciton blue shift with applied voltage in a ⟨111⟩ In0.1Ga0.9As‐GaAsp‐i‐nmultiple quantum well modulator. We have also observed optically induced bistability in a symmetric self‐electro‐optic effect device circuit composed of these modulators. Very large (2.5:1) ratios of photocurrent were obtained with only 0–3 V applied bias.

ISSN:0003-6951    

DOI:10.1063/1.102690

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A number ofp‐substituted benzalbarbituric acid derivatives were synthesized by the reaction ofp‐substituted benzaldehyde with barbituric acid, and their nonlinear optical properties were investigated by using the Kurtz powder test.p‐acetamidobenzalbarbituric acid derivatives were found to exhibit the relatively high second‐harmonic intensity and have the higher thermal stability.

ISSN:0003-6951    

DOI:10.1063/1.102691

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The temporal profiles of metastable F(4P3/2) and Ar(1s5) and emitting F(4D05/2) and Ar(2p2) in a sharp‐edged, pulsed CF4/O2/Ar (87.5/10.4/2.1) discharge are discussed. All four states are so short lived that there is no net accumulation during the discharge pulse and the profiles merely reflect the formation rate. For Ar, electron impact on the ground state leads to both excited states. Their similar profiles mirror the electron excitation function. For excited F, two channels are open: electron impact on CF4, and electron impact on ground‐state F which accumulates during the discharge pulse. The fact that metastable F is rapidly quenched in the gas phase indicates that it is not a major etchant of silicon or silicon nitride as was recently suggested in the literature.

ISSN:0003-6951    

DOI:10.1063/1.102692

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report the first detection by optical means of highly vibrationally excited H2 X1&Sgr;+g(vx=6–11). Vibrationally excited H2was generated using a recently discovered hot‐wire effect in H2gas, and was detected in 40 bands with 2+1 resonantly enhanced multiphoton ionization via the EF state (vEF=0–14). Rotational temperatures are in the range 200–650 K, well below that required for thermal excitation of the observed vibrational levels.

ISSN:0003-6951    

DOI:10.1063/1.102693

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of impurity on the thermal stability of titanium silicide (TiSi2)/single‐crystal silicon (Si) structures has been studied. It is found that nitrogen and oxygen in the TiSi2film significantly influence the morphological changes of a TiSi2/Si structure during high‐temperature annealing at 1100 °C for 2–20 s. Nitrogen impurity improves the thermal stability of the TiSi2/Si structure, whereas oxygen degrades it.

ISSN:0003-6951    

DOI:10.1063/1.103314

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polycrystalline Pd and amorphous PdTa films on Al substrates were studied by a variable energy positron beam and by Rutherford backscattering. Since positron diffusion in the overlayers is limited, the range follows directly from the Doppler broadening as a function of incident positron energy. To observe possible effects of positron backscattering, a sandwich of Al/Pd/Al was studied as well. It was found that the mean penetration depth is not described well byz¯(E)=A(&mgr;g/cm2)×En(E), ifAandnare assumed to be material and energy independent.

ISSN:0003-6951    

DOI:10.1063/1.102694

出版商:AIP    

年代:1990

数据来源: AIP