Showing papers in "Applied Physics Letters in 1963"

The channeling of energetic atoms in crystal lattices

Abstract: Preliminary studies showed that approximates - 1% of 10-kev Cu atoms, starting from lattice sites and slowing down according to the Bohr potential, made very long flights, predominantly in (110) directions. These channeled particies did not move in force-free regions but experienced very many glancing collisions with atoms of the lattice, which steered them into (110) directions. This phenomenon of channeling so dominates the Bohr potential calculations for particles normally incident upon the low index planes of Cu that no reliable statistical inferences about range distributions can be drawn. The probability of channeling increases rapidly with increasing energy for particles incident upon (110) and (100) from energies below 1 kev and for particles incident upon (111) from about 3 kev. In each case, the preferred channel is normal to the crystal surface. In the isotropic case, the probability of channeling remains roughiy constant at about 1% between 1 and 10 kev, the (110) channels being strongly preferred. Channeling is not restricted to fcc crystals. Calculations for diamond and bcc structures al4o show extensive channeling. The existence of channeling may have significant implications for radiation damage theory, since the channeled particies lose their energy in very small increments, thus producing farmore » fewer displacements than would be expected on the basis of conventional cascade theory. (C.E.S.) The hamiltonian of a system of charged particles interacting with the electromagnetic field is investigated. For an arbitrary system the multipole expansion of the interaction between the system and the field is derived by means of a suitable canonical transformation. The transformed hamiltonian is obtained from the hamiltonian of the system by replacing the momenta by the transformed kinetic momenta and by addirg to the hamiltonian a term representing the interaction of the system with the eiectric component of the field. By expanding this interaction term, as weli as the transformed momenta, in powers of the dimension of the system over the wavelength, the multipole expansion of the hamiltonian is obtained. For a system interacting with a classical field the muitipole form of the hamiltonian is exactly equivalent to the originai hamiltonian. For a quantized field this is not true, and the multipole form of the transformed hamiltonian is shown to be equivalent to the original hamiitonian oniy for first-order radiation processes. (auth)« less

Nature of the driving force in flux creep phenomena

Abstract: A more accurate expression for the driving force acting on Abrikosov vortex lines in hard superconductors is derived and used to calculate critical currents in Nb/sub 3/Sn containing cavities. (D.C.W.)

Laser‐induced emission of electrons, ions, and neutral atoms from solid surfaces

Abstract: Studies of various solids--- conductors, semiconductors, and insulators-- -irradiated in a vacuum with a focused beam from a pulsed ruby laser are described. Work was undertaken to detect and identify the ions, electrons, and neutral atoms emitted. The targets studied include Cu, Mo, Ta, W, stainless steel, and graphite, semiconductors of Ge and SiC, and one insulator Al/sub 2/O/ sub 3/. The ion spectra obtained include considerable concentrations of singly and multiply charged species typical of the target and also species representing background gases. (C.E.S.)

Laser‐stimulated raman effect and resonant four‐photon interactions in gases h2, d2, and ch4

Abstract: The output of a giant-pulsed ruby laser was focused into a cell containing the gas, and the output radiation was analyzed. In H/sub 2/ it is found that the frequency difference between lines corresponds to a particular vibration-rotation transition of the molecule. Some evidence for pure rotational transitions in D/sub 2/ was obtained. The resulting spectra in all cases appeared as if a diffusion of energy by discrete steps in frequency space had occurred. (R.E.U.)

Measurement of plasma density using a gas laser as an infrared interferometer

Abstract: A He-Ne gas laser is used as a simple infrared interferometer for measuring electron densities. The optical cavity of the laser corresponds to the reference arm of conventional interferometers. Interference occurs if the radiation from the laser is reflected back into the laser by an external mirror. The system was used to measure the electron density in an argon plasma produced by a pulsed high-current gas discharge. (C.E.S.)

Ion Energies Produced by Laser Giant Pulse

Abstract: Ion energies of approximates 1000 ev were produced by the action of a single giant pulse from a ruby laser. The delivered energy was about 0.2 joules in a pulse having full width at half maximum of about 40 nsec. The peak power was 5.4 Mw. The area of the focal spot was approximately 10/sup -3/ cm/sup 2/. Energies were determined by the ion time-of-flight method. Foils of C, Al, Au, and Ti were target materials. (C.E.S.)

A Simple Method of Measuring Low Uranium Concentrations in Natural Crystals

Abstract: Information from previous investigations on radiationdamaged material was used to provide a simple and sensitive way of measuring uranium concentrations as low as 4 x 10/sup -15/ in micaceous minerals. The linear regions of radiation damage can be enlarged to optical dimensions by etching the mineral in hydrofluoric acid. After the sample is etched to determine the number of background tracks, it is exposed to thermal neutrons in a reactor to induce fission of the uranium impurities. The sample is then reetched to determine the number of new tracks. A formula for calculating the number of fragments crossing a given surface in the interior of a thick sample is used to determine the concentration of uranium in the sample. By using a high purity mica crystal as a detector, this method can be applied to any natural mineral. (C.E.S.)

DIELECTRIC‐WAVEGUIDE MODE OF LIGHT PROPAGATION IN p‐n JUNCTIONS

Abstract: The condition for coherent laser emission from forward-biased p-n junctions [1-3] can be written as [4] [equation 1]... In order for the reported values [1-3] of Ic/A to agree with Eq. (1), must must use values pf d ~50 μ [4]. The question arises as to the nature of the mechanism which could confine the light generated near the junction to such small distances.