Volume 25, Issue 8, 15 October 1974
Index of content:
25(1974); http://dx.doi.org/10.1063/1.1655536View Description Hide Description
Laser‐induced stress waves in iron samples were analyzed by measuring the pressure environment at the back surface of various sample thicknesses. These results were compared with numerical calculations obtained from a one‐dimensional radiation hydrodynamicscomputer code. The experiments were conducted in an air environment under ambient conditions and the metal surfaces were confined by transparent overlays. Peak pressures exceeding 50 kbar were measured with quartz pressure transducers at a laser power density of about 109 W/cm2. Computer predictions agreed favorably with the experimental results and indicated that peak pressures exceeding 100 kbar could be generated by appropriate modifications in the laser environment and target overlay configuration.
25(1974); http://dx.doi.org/10.1063/1.1655537View Description Hide Description
We report CuInSe2/CdS p‐nheterojunctionphotovoltaic detectors which display uniform quantum efficiencies of up to ∼70% between 0.55 and 1.25 μ. Response times as short as 5 nsec have been observed. A weak electroluminescence (0.01% external quantum efficiency) peaking near 1.4 μ has also been observed at room temperature.
25(1974); http://dx.doi.org/10.1063/1.1655538View Description Hide Description
Glow dischargeoptical spectroscopy (GDOS) has been applied to the measurement of impurity profiles in boron‐diffused and ion‐implanted Si samples. The GDOS technique provides a convenient and sensitive probe of boron impurity profiles; results are presented for concentrations below 5×1017 cm−3. For a Si sample which has been subjected to a 1‐h constant source borondiffusion at 1100°C, the measured profile exhibited enhanced diffusion effects typical of previously reported results measured by other techniques. Similarly, a sample implanted with 120‐keV B+ ions to a fluence of 1014 cm−2 exhibited a typical boron distribution. The position of the measured peak concentration corresponded well with that predicted by theory, and the implanted distribution exhibited a prominent tail as reported from other measurements.
25(1974); http://dx.doi.org/10.1063/1.1655539View Description Hide Description
Diffraction gratings have been formed on the surface of germanium using two beams from a ruby laser inclined at an angle to each other. Grating spacings from 2 to 20 μm have been formed that appear to be present only during the illumination and no visible damage is observed. Subsequent illumination with a single beam produces no observable diffracted beams. Permanent gratings in damaged areas can be produced with more intense beams. The intensity of a diffracted order appears to depend on the product of the intensities of the incident beams. Several applications of the temporary grating are suggested.
Threshold reduction in Pb1−x Sn x Te laser diodes through the use of double heterojunction geometries25(1974); http://dx.doi.org/10.1063/1.1655540View Description Hide Description
A systematic study has been made of the effect of the middle active region width in double heterojunctionPb1−x Sn x Te/PbTe laser diodes on the lasing threshold. A fourfold reduction in pulsed threshold over that of comparable single heterojunction lasers is demonstrated in lasers having 4‐μm‐wide middle regions. A comparison is also made between lasers fabricated by liquid phase epitaxy using undoped melts and substrates, and using thallium‐doped p ‐type PbTe layers; the latter is shown to yield thresholds as much as two times lower.
25(1974); http://dx.doi.org/10.1063/1.1655541View Description Hide Description
The temperature (T) dependence of the absorption coefficient β at 10.6 μm of Czochralski‐grown high‐resistivity GaAs and chemical vapor deposited (CVD)ZnSe is measured by laser calorimetry. Experimental data are compared with theoretical curves for intrinsic multiphonon absorption. The temperature dependence of β for GaAs is found to possibly exhibit multiphononlike behavior below ∼450°K, but deviates rapidly from theoretical predictions above ∼500°K. The latter effect may be attributed to an increase in free‐carrier density via thermal ionization from a level near 0.37 eV. The absorption coefficient of CVDZnSe is found to be independent of T over the temperature range investigated, and therefore this material appears to be impurity or surface loss dominated.
25(1974); http://dx.doi.org/10.1063/1.1655542View Description Hide Description
Passive Q switching of the CO2 laser by a new class of saturable absorbers is reported. Results are presented for eight representatives of this class: benzene, chlorobenzene, bromobenzene, m‐dichlorobenzene o ‐dichlorobenzene, m ‐difluorobenzene, pentafluorobenzene, and hexafluorobenzene. These Q‐switching agents operate on a large number of lines in both the 9.6‐ and 10.6‐μ bands. Other aromatic halogens selected on the basis of their absorption spectra are expected to display similar Q‐switch characteristics. This new class of saturable absorbers provides increased flexibility in the production of CO2 laser pulses.
25(1974); http://dx.doi.org/10.1063/1.1655543View Description Hide Description
For laser beams of large aperture with power far above the critical power for self‐focusing, nonlinear propagation instabilities lead to the growth of small‐scale variations in intensity and phase. We report measurements of the growth rate for interference fringes in unpumped ED‐2 laser glass as a function of fringe spacing and intensity. Calculations based on the simplest form of linearized small‐scale instability theory agree approximately with the measured rates, and a more complete linearized treatment predicts the growth rates within experimental error.
25(1974); http://dx.doi.org/10.1063/1.1655544View Description Hide Description
We report the first demonstration of holographic techniques in the vacuum ultraviolet spectral region. Holograms were produced with coherent 1182‐Å radiation. The holograms were recorded in polymethyl methacrylate and examined with an electron microscope. A holographic grating with a fringe spacing of 836 Å was produced and far‐field Fraunhofer holograms of submicron particles were recorded.
25(1974); http://dx.doi.org/10.1063/1.1655546View Description Hide Description
Implanted noble gas atoms of Xe have been used as diffusion markers in the growth study of three silicides: Ni2Si, VSi2, and TiSi2. Backscattering of MeV He has been used to determine the displacement of the markers. We found that while Si atoms predominate the diffusion in VSi2 and TiSi2, Ni atoms are the faster moving species in Ni2Si.
25(1974); http://dx.doi.org/10.1063/1.1655547View Description Hide Description
Deposited films of transition metals (Ti, V, and Ni) have been diffused into LiNbO3 crystals to form low‐loss TE and TM mode optical waveguides. Using Ti, single‐mode low‐loss waveguides which confine the guided light to within ∼1 μm of the surface have been constructed. The choice of diffusion parameters allows independent control of important waveguide parameters.
25(1974); http://dx.doi.org/10.1063/1.1655548View Description Hide Description
Saturated absorption of monochromatic radiation by a Doppler‐broadened transition in NH2D has been measured as a function of intensity. The transition was Stark tuned into coincidence with the 10.6‐μm P(20) line of a CO2 laser. We thereby determined the dependence of the saturation intensity on pressure (5–120 mTorr) and beam radius (0.70–1.25 mm).
25(1974); http://dx.doi.org/10.1063/1.1655549View Description Hide Description
The electron energy distribution function has been numerically determined from the Boltzmann equation for some typical discharge conditions in CO and its mixtures. Collisions of the second kind have also been incorporated in the equation and it is found that the consideration of the second kind of collisions is important when the upper states are highly excited. This is, indeed, the case for the laser active medium.
25(1974); http://dx.doi.org/10.1063/1.1655551View Description Hide Description
Photoconductivity has been studied in p‐type and high‐resistivity n‐type silicon compensated by cobalt. Threshold energies of 0.505, 0.537, and 0.572 eV are observed to be independent of temperature within the experimental accuracy of ±2 meV. This is the first direct experimental evidence of the temperature independence of a deep level in Si. The photoconductivity which is stronger for p‐type samples than for n type leads to its identification as a new deep level 0.521 eV ±2 meV from the valence band; the phototransitions are phonon assisted.
25(1974); http://dx.doi.org/10.1063/1.1655552View Description Hide Description
Series arrays of nearly identical superconducting proximity effect bridges have been fabricated in Nb/Ta thin films. Arrays with up to 500 bridges respond cooperatively to incident radiation and produce voltage steps in response to incident 30–20 000‐MHz radiation at V =(number of bridges in array)×(hν/2e).