Paul J. Brannon

Studies of the spectral and spatial characteristics of shock‐induced luminescence from x‐cut quartz

Spatial and spectral studies of shock‐induced luminescence from x‐cut crystalline quartz as a function of stress level revealed the following information: Crystalline x‐cut quartz has a threshold for emission near the dynamic yield point (about 6 GPa); the spatial distribution of the luminescence from x‐cut quartz changes from an intersecting linear emission pattern to a uniform emission pattern as the stress level increases from 6 to 8 GPa; spectra from x‐cut quartz are band‐like rather than blackbody; crystalline x‐cut quartz has emission peaks near 400 and 600 nm; a change in the 400‐nm emission with time can be correlated to wave interaction times. A discussion of the luminous emission in terms of yielding and other physical mechanisms is given.

Laser feedback: its effect on laser frequency

To estimate the effect of laser feedback, a simple mirror system is considered and the effect on the frequency calculated. The analytical approach used is the same as that used in multifilm calculations. The mirrors are considered in sequence. The complex, Fresnel, amplitude reflection coefficient in conjunction with the next mirror is used to calculate the Fresnel reflection coefficient from the last three mirrors, and so on. This process is continued until the output mirror of the laser is reached and the complex reflection coefficient for the output mirror and all mirrors beyond is determined.

Low-jitter laser-triggered vacuum switch using a composite target

A laser-triggered high-voltage vacuum switch with a composite KCl/Ti target pellet is described. The switch triggers reliably for 532-nm laser input energies of 20 mu J corresponding to a peak irradiance of 1 MW/cm/sup 2/. Jitter times of less than +or-15 ns and delay times of less than 100 ns are observed. Several experiments were performed to explore the operation of the switch. It was found that the amount of energy needed to trigger the switch and the jitter time was strongly dependent on the position of the pellet relative to the cathode. It is noted that the mechanism responsible for the operation of the switch is not completely understood. >

Shock‐induced luminescence from Z‐cut lithium niobate

Shock‐induced luminescence from lithium niobate has been studied in the stress range 1.6–21.0 GPa. Both fast‐framing photography and five‐channel optical pyrometry were used to observe the luminescence. The framing photography showed that the emission pattern is heterogeneous for stresses just above the dynamic yield point. A further increase of the stress resulted in a pattern which was essentially homogeneous to within the experimental spatial resolution of about 30 μm. Narrowband filters and photomultiplier tubes were used in the optical pyrometry experiments. A broadband spectrum with a peak near 700 nm was observed. A plot of the energy dissipated by the shock versus shock stress correlates very well with a plot of the 700‐nm intensity versus shock stress. The mechanism for light emission in lithium niobate appears to be closely related to the dynamic yielding process.

A study of an electron-beam excited atomic xenon laser at high energy loading

Operation of an electron-beam excited atomic xenon laser was investigated at pump rates between 40 W/cm/sup 3/ and 1 kW/cm/sup 3/ with pump times of 1 ms. Effects of cavity loss, gas mixture, and pump rate on laser performance were studied under selected conditions. The variation in laser power in 99.5% argon and 0.5% xenon selectively lasing at 1.73 or 2.6 mu m was investigated as a function of pump power. It was found that the laser pulsewidth was shorter than the pump pulse and increased as the pump rate decreased, consistent with a temperature-induced effect. Lasing with broadband optics was investigated as the xenon concentration was varied and as helium or neon was combined with argon-xenon mixtures. Strong lasing was observed for xenon concentrations up to 20%. Addition of helium resulted in a slight increase in laser pulsewidth and caused lasing at 2.03 mu m to increase at the expense of lasing at 1.73 and 2.6 mu m. >

Ion‐bombardment‐enhanced etching of LiNbO3 using damage profile tailoring

The production of a tailored implant‐damage profile by sequential implantation of ions at several different energies rather than at a single energy can increase the depth and improve the wall smoothness of features produced by ion‐bombardment‐enhanced etching of a solid. This has been demonstrated in the enhanced etching of LiNbO3 by HF following He+ implantation at several energies and fluences selected to produce a relatively flat damage depth profile. The use of lighter ions permits the etching of deeper features than is possible with heavier ions of the same energy. Buried microcracks are observed in heavily implanted Z‐cut samples. Similar microcracks may play an important role in determining propagation losses in ion‐implanted waveguides.

Laser focal spot measurements

The focal spot size for a high‐powered neodymium laser has been determined by measuring the energy passing through pinholes of various sizes and also, by photographing the focused spot. A comparison of the two methods indicated that the photographic method could give misleading results. The spot size was also determined by measuring the absorbed energy by target pellets of various sizes. This method always gave a smaller value than the pinhole method. The difference was attributed to plasma effects.

Improved method of measuring optical waveguide propagation losses

An improved method is reported for determining propagation losses in single-mode optical waveguides that is insensitive to the input light coupling efficiency. (AIP)

A model for the operation of a laser-triggered vacuum low-inductance switch

A new model for the operation of a laser-triggered vacuum switch utilizing a composite target pellet in the cathode is given along with supporting experimental results. It is shown that two separate mechanisms are responsible for the operation of the switch, namely, a thermal mechanism for the initial current flow and an ion regeneration mechanism for the current buildup. The current buildup is strongly dependent upon geometry, as is evident from the experiments with 3- and 1-mm apertures in the anode. The jitter time is primarily determined during current buildup and nearly independent of the laser energy. An ion regeneration mechanism is consistent with the experimental data for current buildup, and a thermal mechanism is consistent with the initial generation of current. >

SHOCK-INDUCED LUMINESCENCE FROM X-CUT QUARTZ AND Z-CUT LITHIUM NIOBATE

The spectral and spatial properties of shock-induced luminescence from X-cut quartz and Z-cut lithium niobate are observed using optical pyrometry and fast framing photography. In both cases the spatial emission patterns are heterogeneous for stresses just above dynamic yielding; the pattern becomes homogeneous to within the spatial resolution of the experiment as the stress is increased further. In addition, the luminescence in both cases increases abruptly after dynamic yielding. The emission spectrum from both samples is band-like rather than blackbody and in the case of X-cut quartz is similar to the photoluminescence from structural defects.