摘要:

A geometrical optics approach is used to calculate the intensity distribution in the image of a small object centered on the axis. The calculations take into account the size of the object as well as the spherical and chromatic aberrations of the lens. The intensity distribution curves, calculated as a function of depth in the image, reveal the existence of a compact high intensity image peak in the caustic region between the paraxial image plane and the plane of least confusion. The intensity distribution curves show that the geometrical resolution is better in the plane with the high intensity peak than in the plane of least confusion. As the object radius approaches zero the plane in which the high intensity peaks occurs moves toward the paraxial plane, and the geometrical resolution approaches zero. For an object of finite brightness the intensity in the image peak also approaches zero. A geometrical errorrgis introduced, which depends on the size of the smallest object providing the required intensity or current in the image peak. The geometrical error and the diffraction error are combined quadratically to obtain a resultant error. An adaptation of the geometrical approach, combined with wave optics, is explored in the case of a point source. Discussions of the intensity‐distribution approach as it affects the resolution calculations in the transmission electron microscope and the emission electron microscope are included. In the case of a probe‐type instrument a perhaps unexpected finding is that a larger source size along with a smaller angular aperture is preferable in some cases to a smaller source size and larger angular aperture.

ISSN:0021-8979    

DOI:10.1063/1.341085

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

It is shown theoretically that semiconductor lasers become bistable with weak optical feedback and that the intensity noise is increased by transitions between the bistable states due to steady‐state fluctuations. The bistability occurs in a narrow range of the feedback magnitude, depending on the phase of feedback light at the semiconductor facet. This is in good agreement with observed noise increase at low frequencies caused by external feedback.

ISSN:0021-8979    

DOI:10.1063/1.341086

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Eleven rare‐gas laser lines in the near infrared and the 1.45‐&mgr;m line in carbon have been pumped with an intense 3.6‐MeV He+dc beam from the Stuttgart Dynamitron accelerator. In one experimental run a40Ar beam was also successfully tested. Laser action was observed in gas mixtures up to several hundred mbar total pressure using a differentially pumped gas target. A maximum output power of 170 mW was observed from He‐Ar laser lines. This shows that ion beam accelerators which are widely used in nuclear physics can also be used as a versatile pumping source for lasers. The maximum power which can presently be provided by the Stuttgart accelerator is about 1 kW (dc). The observed laser lines in the infrared region between 1.15 and 3.07 &mgr;m are known from low‐pressure electrical discharge lasers. The excitation scheme at the relatively high pressures used had been investigated in connection with nuclear pumped lasers by other authors. Ion beam pumping is found to be an interesting pumping method in itself and at present a suitable way to optimize the conditions relevant for nuclear‐pumped lasers as the measurements do not have to be performed in the vicinity of a high flux nuclear reactor.

ISSN:0021-8979    

DOI:10.1063/1.341087

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Laser heating and melting is studied considering the laser‐induced reflectivity variationsR(&tgr;). The study is made for time intervals less than or equal to the transit time using the Fourier series expansion technique together with the differential and integral forms of the heat diffusion equation. The equations obtained for the thickness of the molten layerZ(&tgr;) and the rate of meltingZ’(&tgr;) are no longer quadratic. Computations for a thin silver film of thickness 5×10−5m, subjected to constant laser irradiance of valueq0=9×1010W/m2are carried out. Smaller threshold times required to initiate melting (i.e., damage) than those for the case of constant reflectivity are obtained. It is also found that melting occurs with nearly a constant rate.

ISSN:0021-8979    

DOI:10.1063/1.341088

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A nonuniform layer of deuterium‐tritium (DT) ice inside a spherical inertial confinement fusion (ICF) target held in an isothermal cryogenic environment should be driven toward uniformity by the beta‐decay heat of the tritium. Experiments have been performed at KMS fusion to verify this hypothesis. Two major conclusions may be drawn from the initial results: (1) the beta decay of the tritium does deposit energy in the target, as evidenced by melting of DT ice when the target is well insulated from its surroundings, and (2) solid layers of DT ice sublime because of beta‐decay heat. Both conclusions are reinforced by companion studies with nonradioactive hydrogen‐deuterium (HD) ice in similar targets held under similar experimental conditions.

ISSN:0021-8979    

DOI:10.1063/1.341089

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The feasibility of using the He‐&agr; line of Cu XXVIII at 8.394 keV to pump the 8.410‐keV nuclear transition from the ground level to the (3/2)+ level in169Tm is examined using a collisional‐radiative‐equilibrium plasma atomic model. Numerical calculations of the He‐&agr; line power output are presented for various density, temperature, and size conditions for both laser‐imploded andZ‐pinch plasmas. The interplay between the density, opacity broadening, and the radiating surface area in overcoming the 16 eV difference in transition energies is analyzed.

ISSN:0021-8979    

DOI:10.1063/1.341090

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Microwave diagnostic techniques have been used to measure the radiation temperature and electron density in parallel‐plate capacitively coupled radio‐frequency (2.5 MHz) discharges. Evidence is presented for the existence and importance of an energetic electron beam, produced by the large cathode sheath voltage, which sustains and excites the plasma. The measured radiation temperature of the bulk electrons is 500 K for helium and 800 K for argon. An upper limit on the radiation temperature is obtained for N2(1200 K) and CF4(3000 K) discharges. Measurements of the electron density in helium as a function of electrode spacing show a peak in the electron density that is consistent with the theory of ionization by beam electrons. The electric fields required to carry the rf current by drift in the bulk of the glow are low and consistent with the measured radiation temperature. The implications of these measurements on the nature of the rf plasma‐sustaining mechanism. The voltage distribution, and the electron energy distribution are discussed.

ISSN:0021-8979    

DOI:10.1063/1.341060

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The hollow‐anode discharge, with a hollow‐anode aperture 0.5‐mm i.d., on which the axial‐magnetic field has been applied, is studied. From the hollow anode, outside the discharge tube, an intensive, narrow, and well‐focused beam of fast electrons, more than 30 cm long, is obtained.

ISSN:0021-8979    

DOI:10.1063/1.341061

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The transport of ions through rf glow‐discharge sheaths was simulated with a Monte Carlo method to determine the distributions of ion‐bombardment energy and angle of impact. Several sheath parameters were varied and their effects examined: (1) the type of ion‐molecule scattering (hard sphere, potential field interaction, charge exchange), (2) the ratio of ion and neutral masses, (3) the ratio of the sheath width to collision mean free path, (4) spatially uniform, spatially linear, and time‐dependent (rf) electric fields in the sheath, and (5) the frequency of an rf component in the sheath. The results of the Monte Carlo simulations indicate that the type of elastic scattering (hard sphere or soft sphere) does not significantly change either the impact angle distributions or the scaled ion‐bombardment energy distributions. Charge‐exchange scattering produces a much greater ion‐bombardment directionality and a different shape of the ion‐bombardment energy distribution. The fully developed distributions depend only on the ion‐to‐neutral mass ratio, type of ion‐neutral scattering, and the dc value of the electric field‐to‐pressure ratio at the electrode. Fully developed distributions are reached in approximately three mean free paths in spatially uniform sheath fields and in about six mean free paths for spatially linear sheath fields. The minimum ion directionality was observed when the ion‐to‐molecule mass ratio was approximately unity. Time‐dependent (rf) variation of the sheath field produces features in the ion energy distributions which are similar for both the collisional and collisionless sheaths.

ISSN:0021-8979    

DOI:10.1063/1.341062

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Polycrystalline samples of (CuIn)x(AgIn)yCd2zTe2were prepared by a melt and anneal technique. Guinier x‐ray powder photographs were used to determine equilibrium conditions and lattice parameter values. Two single‐phase fields, with zinc‐blende and chalcopyrite structures, are found to exist in the diagram. Comparison of the experimental results with the expressions proposed by Jaffe and Zunger has been made. It was found that these equations, used with Phillips radii, give good agreement for parameterafor Cu‐rich samples but poorer agreement elsewhere and also forcandc/a. Optical absorption measurements were carried out on most of the samples to determine values of the optical energy gapE0at room temperature. These values ofE0are found to show a nonlinear variation withz. This variation is discussed in terms of the effects ofp‐dhybridization on the valence band and the change in crystal structure.

ISSN:0021-8979    

DOI:10.1063/1.341063

出版商:AIP    

年代:1988

数据来源: AIP