Degree Half Angle Research Articles

Observation of ultrabroadband, beamlike parametric downconversion

We report spontaneous parametric downconversion having an unusually wide spectral bandwidth. A collinear type 1 phase-matching configuration is employed with degeneracy near the zero group-velocity dispersion frequency. With a spectral width of 1080 nm and degenerate wavelength of 1885 nm, the source also emits a high flux of 3.4 x 10(11) s(-1)W(-1) photon pairs constrained to a cone of only approximately 2 degrees half-angle. A rigorous theoretical approach is developed that confirms the experimental observations. The source properties are consistent with an ultrashort photon-pair correlation time and, for a narrowband pump, extremely high-dimensional spectral entanglement.

105 超音速ノズルにおける過膨張流れの特性

An overexpanded flow in a two-dimensional supersonic nozzle with 10 degree half-angle has been experimentally investigated with schlieren observation and wall static pressure measurement, and the experimental results have been compared with the one-dimensional inviscid theory. The characteristics of nozzle flow for various pressure ratios across the nozzle are made clear The range of pressure ratio for the overexpanded flow by the inviscid theory is different from the present experimental results. This is due to the fact that the pseudo-shock is formed in real flows instead of the normal shock.

Atomically sharp silicon and metal field emitters

A method is described for forming atomically sharp silicon tips of less than 10-15 degrees half-angle by utilizing a known oxidation inhibition at regions of high curvature; equally sharp silicon wedges are now made in a similar fashion. The sharp silicon tips serve as the starting point for forming sharp tips of W, beta -W and gold. Field emission data from silicon emitters are compared with Fowler-Nordheim modelling and emission as a function of emitter-anode distance is described. >

Observations of the plasma environment during an active ionospheric ion beam injection experiment

The electrodynamics of the release of neutral beams of a few tens of eV to 200 eV Argon ions in the upper ionosphere is becoming clearer as a result of several rocket flights each having a different location of the Argon release with respect to the diagnostic payload. A volume of about 10 meters radius centered on the Argon release payload is highly turbulent which scatters the Argon ions to angles well beyond the 30 degree half angle emission cone. Broadband wave activity is measured in this volume. The superthermal neutralizing beam electrons become magnetized in this volume for across-field plasma releases. If this volume is not neutralized by field-aligned electron transport it becomes charged and decelerates the Argon ions. Ambient electrons are accelerated near or within this volume to energies of several hundred eV. The mechanism for doing this appears to be due to the wave turbulence rather than any payload neutralization effect. In a much larger volume of cross-field dimension equal to the Argon ion gyroradius (a few hundred meters) the wave activity is predominately near the lower hybrid frequency and also consists of narrow-band waves at ion gyrofrequecies. It is in this volume that ambient ions are accelerated perpendicular to the local magnetic field.

The NBS 14 MeV Absolute Neutron Beam Facility

A 14 MeV absolute neutron beam has been established at the NBS 3 MV positive-ion Van de Graaff Accelerator Laboratory. The T(d,n)? reaction is used for the production of the 14.1 MeV neutron flux with a source strength of 108 n/sec. The neutron flux is absolutely determined by the measurement of the associated alpha particle rate in a silicon surface barrier detector positioned at 84 degrees with respect to the beam axis. The facility may be used to measure the absolute response of active neutron monitoring devices with high accuracy. The neutron background contributions may be eliminated in the calibration measurements by utilizing the coincidence between the device and the solid state alpha detector. This method allows a neutron flux in a cone of 2 degree half angle to be placed at 90 degrees with respect to the beam axis.

Stopping powers of copper, silver and gold for protons and helium ions of low energy

Protons and helium ions in the energy range 4-16 keV have impinged on free films of copper, silver and gold of thicknesses from 300 to 700 AA. The stopping powers have been determined by measuring the energy spectra of the ions transmitted within a cone of 3 degrees half-angle. As for the stopping power for helium ions, the nuclear stopping power is very small compared with the electronic stopping power in this method. The experimental results show that the dependence of the electronic stopping power on the ion velocity is almost in quantitative agreement with the Lindhard, Scharff and Schiott (LSS) theory.

X-Ray Telescope for an Orbiting Solar Observatory

The X-ray experiment described here was designed to monitor the intensity, energy distribution, and time variations of solar X-rays, and to measure the intensity and angular distribution of X-rays over the celestial sphere. The detector, which operates between about 7 to 200 Kev, will also monitor local effects due to cosmic rays, trapped particles, and albedo gamma rays The telescope consisted of a thin NaI (T1) crystal-phototube assembly surrounded by a 10.5-lb cylindrical cup-shaped CsI(T1) shield crystal. The shield, connected in anticoincidence, had a 2-cm wall and defined a field of view of 13 degrees half-angle for the NaI detector. The detector had an area of 9.3 cm2 and a geometry factor of 1.5 sterad-cm2. The charge-energy relationship was divided into eight logarithmically spaced pulse-height channels. Integral rates of the shield crystal were monitored for two thresholds, set at 85 Kev and 3.2 Mev, respectively. Binary and logic circuits provided scaling, storage, and directional information for each channel, and conditioned the data for transmission through the spacecraft telemetry. The experiment is to be flown on the NASA S-57 Orbiting Solar Observatory-C, scheduled for launch in early 1965. The observatory is to be placed in a near circular orbit at 300 nautical miles at an inclination of 33 degrees to the equator. The design lifetime of the instrument is six months. Performance checks with ground observations and with high-altitude balloons indicated the counting rate due to phototube noise to be 3 counts per minute for events > 7 Kev.

Experimental Study of the Effect of Field of View on Transmission Measurements

The ratio of the amounts of scattered and direct radiation received from a 4π source has been measured in the San Francisco Bay Area for source-receiver distances of 1.18, 4.33, 6.79, 9.81, and 14.37 miles. A large flashlamp surrounded by a frosted globe was used as the source. The receiver consisted of any one of five combinations of Wratten fiters and photomultiplier tubes having peak responses at 0.40, 0.50, 0.70, 0.83, and 0.90 μ and feeding into an oscilloscope, the screen of which was photographed. A device for controlling the field of view of the receiver allowed choice of fields of view from 4 degrees to 58.33 degrees half-angle, and an occulter allowed the direct radiation to be blocked out if desired. It has been found that for a given field of view the ratio of scattered to direct radiation received from such a source under no overcast conditions is greater the shorter the wavelength and that for source-receiver distances of up to about 7 miles this ratio is approximately proportional to the optical thickness (path length times attenuation coefficient) of the path. For the source-receiver distances greater than 7 miles and a given attenuation coefficient and field of view, the ratio in question has been found to decrease slowly with increasing distance.