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Direct optical triggering of an avalanche transistor with a short laser pulse has been demonstrated. In some applications this system provides a compact low-jitter replacement for a laser-triggered spark gap. The technique has been applied to generating the gating and sweep voltages in a picosecond streak camera for laser pulse diagnostics where it eliminates the need for multiple beam splitters and long delays. The ``trigger'' avalanche transistor was placed as one of a series string of avalanche transistors. A portion of the switched-out laser pulse to be diagnosed was focused onto the trigger transistor chip. Nanosecond-rise kilovolt waveforms are thus generated with time jitter of the entire system being less than 100 psec.

Beam control and diagnostic systems are required to align the National Ignition Facility (NIF) laser prior to a shot as well as to provide diagnostics on 192 beam lines at shot time. A design that allows each beam's large spatial filter lenses to also serve as objective lenses fw beam control and diagnostic sensor packages helps to accomplish the task at a reasonable cost. However, this approach also causes a high concentration of small optics near the pinhole plane of the transport spatial filter (TSF) at the output of each beam. This paper describes the optomechanieal design in and near the central vacuum vessel of the TSF.

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Irising time of microchannel plaie intensifiers with quartz cathode windows has been reduced to less than 100 ps. This is achieved by application of a metal underlay to reduce cathode substrata resistance. The first approach uses a 50%-transmissive Uniform nickel heavy underlay, while the second approach uses a 96%-transmissive nickel mesh.For the heavy underlay, approximately 5 nm of nickel is evaporated over the cathode side of the quartz window. For the mesh underlay, approximately 750 nm of nickel is sputtered onto the window and coated with photoresist, which is exposed through a mask of 100-micron-square spaces defined by 3.5-micron-wide lines. The photoresist is developed and washed off, exposing the nickel covering the square areas. At this point, photoresist still covers the nickel over the 3.5-micron-wide wires, protecting them when the exposed nickel covering the squares is etched away. Removal of the remaining photoresist leaves only the nickel wires, which have been reduced to 2 microns in width due to sideways etching during removal of the squares.As a prototype effort, Lawrence Livermore National Laboratory (LLNL) purchased two 1 8-mm heavy underlay tubes from Hamamatsu Photonics and formed a mesh underlay on faceplates which Hamamatsu used for construction of two additional tubes. Measurements of irising time were made on these four tubes. Irising is characterized by a bright ring, seen first at the edge as it propagates toward the center. The time lag is caused by the distributed time constant of the substrata resistance and the cathode-to-MCP capacitance. Since the capacitance is fixed by restraints of tube geometry, our goal was to reduce the distributed resistance sufficiently to achieve sub-nanosecond irising times. Testing showed no irising on one tube of each type of underlay. With these encouraging results, LLNL and Nanostructures refined the mesh application technology, and LLNL procured eight mesh tubes from ITT using meshes formed by Nanostructures. An additional 8 tubes with a 50% transmissive heavy underlay were procured from Hamamatsu. Testing of these tubes also showed no detectable irising, which leads us to conclude that tubes can be made with irising clearly faster than the time resolution of our measurement system, which we estimate to be less than 50 Ps.