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15 Nov 1966

Volume 9, Issue 10, pp. 353-387


COHERENT RADIATION FROM VOLTAGE‐BIASED WEAKLY CONNECTED SUPERCONDUCTORS

J. E. Zimmerman, J. A. Cowen, and A. H. Silver

Appl. Phys. Lett. 9, 353 (1966); http://dx.doi.org/10.1063/1.1754609 (3 pages) | Cited 25 times

Online Publication Date: 30 November 2004

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This Letter reports the generation of coherent radiation with voltage‐biased superconducting point contacts at both 30 MHz and 10 KMHz. The method of voltage biasing stabilizes the frequency of the emitted radiation against external noise sources and is tunable over a wide frequency range. We have optimized the electromagnetic coupling of the superconducting generator to the receiver and detected at least 5% of the generated power at 30 MHz. The relation1 V = Φ0ν, where Φ0 is the flux quantum, is satisfied. Furthermore, we have observed harmonics, V = nΦ0ν, and subharmonics, nV = Φ0ν, of this relation. The frequency stability of the emitted radiation was limited by the stability of the bias supply and was measured to be 10−5 at 30 MHz.

INFRARED BIREFRINGENCE OBSERVATIONS ON ELECTRON‐BOMBARDED SILICON

Gene J. Carron

Appl. Phys. Lett. 9, 355 (1966); http://dx.doi.org/10.1063/1.1754610 (3 pages) | Cited 6 times

Online Publication Date: 30 November 2004

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Polarized infrared radiation was used to study the birefringence surrounding localized thermal strains in single‐crystal silicon due to electron beam bombardment. These localized spots had previously exhibited four‐lobed rosette stress patterns when examined by x‐ray topography. The interest lies in the crystal optics effects relating these observed phenomena.

OPTIMUM HETERODYNE DETECTION AT 10.6 μm IN PHOTOCONDUCTIVE Ge:Cu

M. C. Teich, R. J. Keyes, and R. H. Kingston

Appl. Phys. Lett. 9, 357 (1966); http://dx.doi.org/10.1063/1.1754611 (4 pages) | Cited 19 times

Online Publication Date: 30 November 2004

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A measurement of the signal‐to‐noise ratio and minimum detectable power for heterodyne detection of scattered radiation at 10.6 μm has been made. Using photoconductive Ge:Cu as the detector, the observed minimum detectable power, at a frequency of 70 kHz and in a bandwidth of 270 kHz, was 3.5 × 10−14 W. This corresponds to a minimum detectable power of 1.3 × 10−19 W in a 1‐Hz bandwidth, which is within a factor of 10 of the theoretically perfect photon counter.

SPATIALLY RESOLVED LASER HETERODYNE MEASUREMENTS OF PLASMA DENSITIES IN WEAKLY IONIZED GASES

J. T. Verdeyen, B. E. Cherrington, and M. E. Fein

Appl. Phys. Lett. 9, 360 (1966); http://dx.doi.org/10.1063/1.1754612 (3 pages) | Cited 10 times

Online Publication Date: 30 November 2004

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See Also: Erratum

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A two‐wavelength He:Ne laser heterodyne system has been successfully used to measure electron number densities in the range from 4 × 1012 cm−3 to 1011 cm−3, over a path length of 24 cm. These experiments were performed on a single‐shot basis in pulsed argon discharges. The spatially resolved laser measurements compared quite favorably with integrated electron density measurements made with a microwave cavity operating in the TM010 mode.

SURFACE EXCESS CONDUCTANCE IN GERMANIUM TUNNEL JUNCTIONS VIA SURFACE STATES

J. E. Alberghini and R. M. Broudy

Appl. Phys. Lett. 9, 362 (1966); http://dx.doi.org/10.1063/1.1754613 (3 pages)

Online Publication Date: 30 November 2004

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Following cleavage through p‐n junctions on degenerate n‐type and p‐type germanium in liquid nitrogen, a large additional exponential contribution to the excess current has been observed. It is established that this excess is associated with the clean surface at the junction. Inversion layer conduction is shown to be negligible. Experimental evidence supports the interpretation that the surface excess is due to tunneling via surface states.

INTERACTION OF LITHIUM WITH IMPURITIES AND DEFECTS IN SILICON

P. H. Fang and Y. M. Liu

Appl. Phys. Lett. 9, 364 (1966); http://dx.doi.org/10.1063/1.1754614 (3 pages) | Cited 7 times

Online Publication Date: 30 November 2004

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Defects in silicon p‐on‐n solar cells with a lithium‐diffused n region, produced by electron irradiation and spontaneously annealed at room temperature, are interpreted as lithium atoms.

AN INVESTIGATION OF THE EFFECT OF GAS ADDITIVES ON THE ELECTRON TEMPERATURE AND DENSITY IN A CO2 LASER DISCHARGE

P. O. Clark and M. R. Smith

Appl. Phys. Lett. 9, 367 (1966); http://dx.doi.org/10.1063/1.1754615 (3 pages) | Cited 13 times

Online Publication Date: 30 November 2004

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The radial variation of electron temperature and density with partial gas pressures in a CO2☒N2☒He laser discharge is measured using double‐probe and microwave resonance techniques. In a 22‐mm‐diam discharge tube the optimum partial gas pressures for maximum laser power correspond to an electron temperature of 3 eV and a density of 3 × 109 cm3. The radial electron density profile is compatible with measured gain profiles. The results indicate that the role of He in the excitation mechanism is not due to a reduction in electron temperature.

PULSED OPERATION OF CO2☒N2☒He LASERS

P. O. Clark and M. R. Smith

Appl. Phys. Lett. 9, 369 (1966); http://dx.doi.org/10.1063/1.1754616 (4 pages) | Cited 8 times

Online Publication Date: 30 November 2004

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The amplitude and time behavior of the pulsed output from a 10.6‐μ CO2☒N2☒He laser is investigated as a function of partial gas pressures and discharge current. Nearly two orders of magnitude increase in output power is obtained compared to CW operation. The time behavior of the laser pulse indicates that electron excitation processes dominate in populating the upper laser level.

EFFICIENT MICROWAVE SHEAR‐WAVE GENERATION BY MODE CONVERSION

E. G. H. Lean and H. J. Shaw

Appl. Phys. Lett. 9, 372 (1966); http://dx.doi.org/10.1063/1.1754617 (3 pages) | Cited 3 times

Online Publication Date: 30 November 2004

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It is found that efficient conversion from longitudinal acoustic waves to shear waves is possible in YAG by surface conversion at an incline surface, with both the input and output waves traveling along crystal axes. Using this process, existing efficient longitudinal‐wave transducers are applicable to shear‐wave generation. Laser beam probe measurements indicate that the surface conversion loss is of the order of 0.1 dB at 1461 MHz, and that the shear wave column has approximately the expected cross‐sectional shape.

THEORY OF THE OPTICAL FREQUENCY TRANSLATOR

C. G. B. Garrett and M. A. Duguay

Appl. Phys. Lett. 9, 374 (1966); http://dx.doi.org/10.1063/1.1754618 (4 pages) | Cited 6 times

Online Publication Date: 30 November 2004

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The Duguay, Hargrove, Jefferts frequency translation experiment is analyzed in terms of superposition of side bands. It is shown that a Gaussian input pulse leads, in a good approximation, to a Gaussian output pulse translated in frequency, so long as the modulation index is not so large as to lead to a translation, in units of the inter‐mode spacing, of the order of the cube of the number of modes of appreciable amplitude in the input pulse.

SUPERCONDUCTING LENS FOR ELECTRON MICROSCOPY

Norihisa Kitamura, Michael P. Schulhof, and Benjamin M. Siegel

Appl. Phys. Lett. 9, 377 (1966); http://dx.doi.org/10.1063/1.1754619 (4 pages) | Cited 2 times

Online Publication Date: 30 November 2004

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Arrangements of superconducting materials have been investigated to obtain objective lenses with the lowest possible spherical aberration coefficient (Cs) for the electron microscope. Various configurations of Nb3Sn in ferromagnetic containers giving current loops of small radii which produce axially symmetric magnetic fields with high peak intensities and narrow halfwidths were studied. The axial field distributions were measured (bismuth probe) and optical parameters and spherical aberration coefficients were calculated. Available superconducting materials appear to set a limit of Cs ≃ 0.4 mm and Cs ≃ 1.8 mm for 100 kV and 1000 kV electrons, respectively (bore diam, 5 mm).

NOISE STUDIES IN UNIFORM AVALANCHE DIODES

Roland H. Haitz and Fred W. Voltmer

Appl. Phys. Lett. 9, 381 (1966); http://dx.doi.org/10.1063/1.1754620 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2004

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This Letter reports avalanche noise studies on microplasma‐free guard‐ring avalanche diodes. The low and high frequency approximations of Hines' theory are compared with experimental results at 1 kHz and 3 to 9 GHz, respectively. Good agreement is found between experiment and theory at both low and high frequencies. The open‐circuit spectral voltage density is white up to the avalanche frequency ωa and decreases inversely with current. For ω ≫ ωa the spectral noise power density falls off with ω4.

ELECTRON‐HOLE GENERATION IN GaAs

Esther M. Conwell

Appl. Phys. Lett. 9, 383 (1966); http://dx.doi.org/10.1063/1.1754621 (3 pages) | Cited 3 times

Online Publication Date: 30 November 2004

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Experimental findings have been interpreted by Copeland as indicating that the multiplication rate α(E) of carriers in GaAs has a narrow peak between 3 and 10 kV∕cm. It is argued here that theory can account for a sizeable α at these low fields, but that, rather than having a maximum and decreasing to zero again, α will continue to rise. The proposed variation of α appears to be more consistent with experimental results.

VELOCITY DISTRIBUTION MEASUREMENTS OF MOLECULAR BEAMS SCATTERED FROM SOLID SURFACES

Otto Friedrich Hagena

Appl. Phys. Lett. 9, 385 (1966); http://dx.doi.org/10.1063/1.1754622 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2004

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Using a nozzle‐type molecular beam with highly uniform velocity and high intensity and a sensitive time‐of‐flight detection system allows the measurement of the complete distribution of speeds after scattering the incident beam from a solid surface. With a ``dirty'' metal target at room temperature and argon as beam gas, it is found that the thermal spread of velocities in the scattered beam is at least three times larger than the thermal spread of velocities in the incident beam. While a complete thermal accommodation of the incident atoms would result in the same speed distribution for all scattering angles, the measurements show an angular dependence of the thermal spread and the mean speed of the scattered atoms.
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