摘要:

Using spectroscopic ellipsometry we have studied a series of virgin and germanium‐implanted crystalline silicon samples oxidized at 900 and 1000 °C. The thickness of the oxide in the virgin and implanted sample was accurately determined and found to be in agreement with the results previously obtained by single‐wavelength ellipsometry. The interface structure between the silicon substrate and the oxide layer of all the samples was investigated in detail. We find that the interposing layer between the oxide and the silicon substrate is composed of a thin layer of crystalline germanium‐silicon alloy. A brief discussion on the strain and quantum confinement of the interface that may affect the calculated composition is also presented. The interface thickness was found to be slightly larger to that obtained by high‐resolution transmission electron microscopy measurement for samples implanted at higher doses. A plausible explanation for the discrepancy is provided.

ISSN:0021-8979    

DOI:10.1063/1.345760

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The partial pressure of vibrationally excited hydrogen has been measured in a flowing gas using the technique of vacuum ultraviolet laser‐induced fluorescence. In most of the studies H2(v=1) was generated with a microwave discharge. For this source we measured in detail the effects of the partial pressures of H2and Ar, the flow rate, the microwave power, and the construction of the flow tube. A more limited study was also performed using a thermally heated flow tube.

ISSN:0021-8979    

DOI:10.1063/1.345761

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The generation and transport of a 1‐MV, 5‐kA, 50‐ns annular proton beam has been studied. The diode is magnetically insulated with a full‐cusp field geometry. Beam transport in a 6‐kG axial magnetic field is measured for injection into vacuum and neutral gas. The neutral gas background is supplied by a fast puff valve system. The gas background is found to enhance the space‐charge neutralization of the beam. Under these conditions the beam divergence is <1° and the annular profile is maintained throughout the 30‐cm transport region. We discuss a simplified model of the beam injection process to explain the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.345762

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A rigorous electromagnetic theory of the common sidewall, single‐hole directional coupler is presented. The characteristics of the directional coupler are obtained retaining the propagating modes as well as the evanescent modes, and the effect of the evanescent modes is determined. The standing‐wave ratio at the input port, the directivity, the transmission, and the coupling factors, together with their spectral responses, are investigated. Maximization of the power coupled to the output port with respect to the aperture width and the optimization with respect to the variation in the width of the waveguide are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.345763

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A series of bulk proton‐exchanged lithium niobate waveguides has been prepared by using concentrated sulfuric acid as the proton source and varying the time and temperature of the exchange process. The optical and physical properties of the proton‐exchanged lithium niobate layer have been measured and found to be essentially identical to proton‐exchanged layers obtained by other workers using the benzoic acid process. Sulfuric acid offers a number of advantages over benzoic acid as a proton source, including a wider temperature liquid range and a greater ease of handling in a clean‐room environment.

ISSN:0021-8979    

DOI:10.1063/1.345764

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The nonlinear optical coefficients of lithium triborate LiB3O5(LBO) have been determined by the method of Maker fringes at &lgr;=1.079 &mgr;m. It is found that these coefficients relative tod36for potassium dihydrogen phosphate ared31=∓2.51 (l±0.09),d32=±2.69 (l±0.12),d33=±0.15 (l±0.10),d15=∓2.30 (l±0.22), andd24=±2.52 (l±0.20). The phase‐matching conditions, effective second‐harmonic generation (SHG) coefficients, walk‐off angles, and acceptance angles for SHG at &lgr;=1.079 &mgr;m are also investigated. The figures of merit of LBO in different cases are then compared with those of potassium dihydrogen phosphate (KDP), &bgr;‐barium metaborate (BBO), and potassium titanyl phosphate (KTP) crystals. All these figures combined with the damage thresholds of the crystals show that an LBO crystal may operate better than KDP and BBO crystals for frequency conversions of a tightly focused Nd:YAlO3(YAP) or Nd:Y3Al5O12(YAG) laser and also a dye laser.

ISSN:0021-8979    

DOI:10.1063/1.345765

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The radiation emitted by electromagnetic sources placed both inside and outside of a homogeneous sphere of chiral media is studied using an exact formulation. For both cases, dyadic Green’s functions are found in terms of spherical vector wave functions. The radiated fields and radiation resistance are examined for a dipole located at the center of the chiral sphere. For this case, it is shown that by choosing the sphere’s size and material parameters properly, purely circular polarization can be achieved in the far field. It is also demonstrated that the radiation resistance of the dipole can be increased.

ISSN:0021-8979    

DOI:10.1063/1.345766

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Emission and absorption spectra of (5% Er) BaY2F8were studied at 300, 77, and 4.2 °K. Stark‐level positions were determined from the liquid‐helium absorption spectra. Emission spectra were excited with a UV flash lamp and 1.53‐&mgr;m radiation from an Er:glass laser; in the latter case, the visible and near‐IR fluorescence of the Er3+ions was excited through a multiphoton upconversion process. The lifetimes of Er3+‐ion‐excited states were measured at 300 and 77 °K. Laser action was stimulated at 0.85, 1.73, and 2.796 &mgr;m in a (5% Er) BaY2F8laser rod using the transitions4S3/2→4IJ, whereJ=13/2, 9/2, and4I11/2→4I13/2, respectively. A Xe flash lamp was used for optical pumping. The latter two laser transitions were also pumped through upconversion of 1.53‐&mgr;m radiation of the Er:glass laser. The cross‐relaxation ion‐pair conversion coefficient for the4I13/2levels of the Er3+ions in BaY2F8was calculated to be &agr;=3.7×10−17cm−3 s−1.

ISSN:0021-8979    

DOI:10.1063/1.345767

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Investigations of acousto‐optic interactions between guided optical waves and Bleustein–Gulyaev surface acoustic waves in gallium arsenide and other piezoelectric cubic crystals indicate very low light diffraction efficiency. The diffraction efficiency is controllable, however, by varying the penetration depth of the surface wave. A simple and effective method of detecting Bleustein–Gulyaev waves using a plane optical wave is also presented.

ISSN:0021-8979    

DOI:10.1063/1.345768

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Spectroscopic measurements were made on a nitrogen nonblown arc in extinction at atmospheric pressure seeded with copper vapor produced by the anode. The experimentally determined axial temperatures and total line intensities were compared to theoretical values obtained from a model based on mass and energy conservation equations. This comparison validated the model and showed that for an initial current of 25 A, the concentration of copper decreases at 0.5 mm from the anode as soon as the electric field is cut but remains more or less constant for about 150 &mgr;s in the region of plasma at around 2.5 mm from the anode. This is mainly due to the copper diffusion mechanisms involved. The model allowed the influence of copper on the evolution of the conductance of a nitrogen arc during extinction to be calculated. In particular it was seen that a proportion of copper as low as 10−4markedly changed the conductance of the arc. Moreover, when the conductance of pure nitrogen has dropped by a factor of 40 compared to the initial value, that of a mixture containing 99.9% nitrogen and 0.1% copper has only decreased by a factor of 4.

ISSN:0021-8979    

DOI:10.1063/1.345769

出版商:AIP    

年代:1990

数据来源: AIP