摘要:

A formalism describing the conversion of radiation energy into work can be constructed in terms of energy and entropy fluxes. This leads, among others, to the Landsberg efficiency, a formula expressing an upper bound to photothermal solar energy conversion. The relationship between the above approach and the viewpoint of endoreversible thermodynamics is investigated. An extension to photovoltaic solar energy conversion is formulated. A generalization of the Landsberg formula, for a solar energy converter with arbitrary bandgap, is presented.

ISSN:0021-8979    

DOI:10.1063/1.354503

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For large inertial confinement fusion deuterium‐tritium targets, a way to diagnose &agr; slowing might be via capture reaction &ggr; rays. Calculations are presented for two such methods: one uses the &agr;+T direct capture &ggr; rays, the other is based on a series of resonant &agr;‐capture reactions. For small targets (&rgr;R≤0.02 g/cm2), the total &agr;+T &ggr;‐ray yield relative to the DT neutron yield is temperature independent and proportional to the &rgr;Rvalue. For large targets (&rgr;R≥0.2 g/cm2), this quantity becomes temperature dependent and &rgr;Rindependent. Some experimental aspects are discussed.  

ISSN:0021-8979    

DOI:10.1063/1.354504

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Specific primary ionization induced by minimum ionizing electrons has been measured in several gases and vapors. Charges deposited by &bgr;‐electrons in a low‐pressure gas were collected, amplified by a multistep gaseous electron multiplier, and counted. The high counting efficiency of the multiplier provided results of systematically higher values as compared to existing data. The respective values of the specific primary ionization in CH4, C2H6, C3H8,i‐C4H10, argon, dimethylether, triethylamine, and tetrakis(dimethylamino)ethylene are: 0.034, 0.065, 0.095, 0.12, 0.03, 0.082, 0.195, and 0.370 clusters/cm Torr. The experimental method is presented and the results and their accuracy are discussed.

ISSN:0021-8979    

DOI:10.1063/1.354505

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The source area of electron field emission from ultrasharp ⟨111⟩‐oriented tungsten tips terminated by a few (down to one single) atoms is confined to the very end of the tip, thus forming an atomic size electron source. The most remarkable emission property of such tips, the angular dispersion of the emitted electron beam, is measured both qualitatively and quantitatively for well‐defined atomic arrangements at the tip apex and also for a wide range of applied electric fields and currents. It is shown that only pyramidally shaped tips emit electrons in sharp beams, with small opening angles down to less than 3°. The results suggest, in contrast to existing theories, that mesoscopic parameters, as the overall shape of the tip apex (on a scale of a few nanometers) and the associated patch field distribution, might play a crucial role in focusing the beam.

ISSN:0021-8979    

DOI:10.1063/1.354506

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

High purity, 1 MV, 50 ns, 300 A/cm2lithium beams have been produced using an extraction diode driven by Cornell’s Light Ion Accelerator. Both passive and active anodes were studied with the highest‐purity beams being generated by active anodes. These anodes were approximately 200 cm2in area and consisted of 0.1 &mgr;m films of Al and LiF evaporated onto a glass substrate. The anode plasma was formed by using a plasma opening switch to divert 50 kA from the main power pulse through the Al foil for 20 ns. Without glow‐discharge cleaning, the ion beam produced by the LiF Al anode was over 55% hydrogen and only 20% Li+. In order to remove impurities, especially the hydrogen, the anodes were cleaned with a 110 mA, 33 W, 60 Hz glow discharge. The stoichiometry of the ion beam after discharge cleaning was 65% Li+, 20% Al+2, and 15% H+. The results are presented and a model of the cleaning mechanism is discussed.

ISSN:0021-8979    

DOI:10.1063/1.354507

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have prepared films of polymethyl methacrylate in which fullerenes (a mixture of C60and C70) are uniformly embedded. By performing both degenerate four‐wave mixing experiments and irradiance‐dependent transmission measurements with nanosecond laser pulses of 608‐nm wavelength, the third‐order nonlinear optical susceptibility of these films is determined to be of the order of 10−10esu. This susceptibility is dominated by its imaginary part. Excited‐state absorption is the main mechanism responsible for the observed nonlinear susceptibility.

ISSN:0021-8979    

DOI:10.1063/1.354508

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Addition of helium to an Ar/Xe gas mixture has been shown to significantly improve the fission‐fragment excited 1.73 &mgr;m atomic xenon laser performance. Using narrow band dielectric laser cavity mirrors to suppress the 2.03 &mgr;m atomic xenon transition, the 1.73 &mgr;m laser power efficiency varied between 1% and 3% for total pressures of 520–1550 Torr, He/Ar ratios of 3/1–16/1, and pump rates of 5–40 W/cm3. For a constant energy loading, the FWHM of the laser pulse with respect to the pump pulse increased by a factor of 2.5 when argon was replaced by helium. Small signal gain varied between 0.1%/cm and 1.0%/cm. The implication of helium substitution on the Ar/Xe laser kinetics is discussed.

ISSN:0021-8979    

DOI:10.1063/1.354509

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Optical probing of transverse ‘‘width’’ surface modes of magnetostatic waves (MSW) in narrow yttrium iron garnet–gadolinium gallium garnet waveguides 1.14‐ and 0.49‐mm wide has been performed. It has been shown that the resolution of the optical technique using four first couples of optical waveguide modes TEi, TMi(i=0,1,2,3) is sufficient to detect diffraction peaks of numerous transverse magnetostatic modes (n=1,2,3,4,5,6). The method makes it possible to directly measure the efficiency of excitation of transverse MSW modes (symmetric as well as antisymmetric) in a narrow channel waveguide, which cannot be realized by means of microwave measurements.

ISSN:0021-8979    

DOI:10.1063/1.354510

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Third‐order nonlinear optical properties of As2S3chalcogenide bulk glass are studied experimentally. Third‐harmonic generation (THG) measurement shows the value of the third‐order susceptibility &khgr;(3)to be 5.6×10−19m2/V2(1.0×10−11esu) at the funda‐ mental‐light wavelength of 2.1 &mgr;m. This value is more than 300 times that for a silica glass. The dependence of the THG &khgr;(3)on the wavelength has been measured, which indicates the &khgr;(3)enhancement effect due to three‐photon resonance. Optical Kerr shutter operation is also achieved using the chalcogenide glass. The nonlinear refractive index ofn2=6.8×10−18m2/W is obtained at the gate‐light wavelength of 700 nm. This value ofn2agrees with that estimated from the THG measurement. Other nonlinear effects such as two‐photon absorption for the gate light are discussed.

ISSN:0021-8979    

DOI:10.1063/1.354511

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Extinction cross sections normalized to particle volume for two fibrous graphitic aerosols were measured at 0.319 cm (94 GHz) and 0.857 cm (35 GHz). Characterization of the aerosol was performed using several techniques, that is, dosimetrically, through time correlation of millimeter wavelength extinction signals with scattered radiation at much shorter wavelengths, through time correlation with a nearly colinear measurement of extinction at visible wavelengths and using a purpose‐built time resolved particle collector system. Results compare well with existing detailed theory.

ISSN:0021-8979    

DOI:10.1063/1.354512

出版商:AIP    

年代:1993

数据来源: AIP