Development of Experiment for Materials Studies at the Z-Beamlet Laser Facility Lasers enable us to study the state of materials and the dynamics of material processes. The Line-VISAR measures the material velocity. Incoming Light Injection to Fiber Fiber 50/50 Beamsplitter Periscope 3” Mirror 15 cm f.l. achromat 10 cm f.l. achromat Streak Camera CCD Camera Particle velocity is determined with VISAR and 2D Interferometry. Using the Equation of State of a material, we can establish shock velocity, pressure, and compression. Shock loading with lasers enables us to study material melting. Lasers enable us to determine the material strength at higher strain rates. Pump beam VISAR Probe The shock experiments that we perform at Z-Beamlet are pump-probe style experiments. The VISAR (Velocity Interferometer System for Any Reflector) measures a Doppler shift in the probe light. By using a streak camera, we can image a line from the target. This gives both spatial and temporal information. Upon retrieving the phase out of an interferogram, the velocity is found by multiplying the phase by the velocity per fringe constant. When the pump beam hits the target, ablation of the material into vacuum initiates a shock wave that propagates toward the back surface. An advantage to using Z-Beamlet is that we can reach pressures necessary to melt aluminum over a large area. (In order to drive a 1D shock, the ratio of laser spot size to target thickness must be ≥ 3:1) Interferogram and maximum velocity profile for 50 micron Aluminum on LiF impacted at ~5x10 12 W/cm 2, giving a maximum pressure of 1.4 Mbar and maximum density of 1.7 ρ 0. The equation of state used was: U S =5.386 um/ns U P Key Design Features Fast Optics Optical Fiber Mach-Zehnder interferometer Douglas Allen Dalton Will Grigsby Aaron Bernstein Despina Milathianaki Todd Ditmire Eric Taleff Jonathan Brewer Richard Adams Patrick Rambo Larry Ruggles Ian Smith John Porter 2D short pulse diagnostics give an advantage of looking at the shock breakout at a point in time. Spall is the planar separation of material due to tensile stress, which is induced by crossing rarefaction waves. The spall pressure and strain rate can be found from an interferogram. 2 ns 1.79 mm 2 ns 1.79 mm Build pulse stacker for events that occur on a longer time scale. Continue developing other short pulse techniques. Implement use of a phase plate to produce more uniform shocks. Further developments are needed to make future progress. Reflectivity/Interferometry Probe Through Fresnel’s Reflectivity equation, material conductivity can be found. The 2D interferometer gives the interface/free surface displacement at a snapshot in time. Mapping out position versus time, the interface/free surface velocity can be determined. Reflectivity ImagePosition Interferogram 3 mm Although this is not the data that we expected, we can redesign the system for a faster collection optic. We previously used ~f/16 collection optic, but now want an f/3 optic. 50 um Aluminum (Melt) 350 um Aluminum (Spall) (100) Lithium Fluoride (Melt) Nearly complete loss of light in shocked region By putting the image plane at the output beamsplitter, adjustments optimizing fringe contrast are decoupled from adjustments optimizing fringe orientation and fringe spacing. Uneven Shock Breakout Velocity (microns/ns) Time (ns) Interferogram of a 350 micron free standing target impacted at ~7x10 11 W/cm 2. Beamsplitters Reflecting Anti-Reflecting Etalon Mirror Reflecting Anti-Reflecting Image Plane To Streak Camera To Camera 7.5 mm SEM image showing the back surface of a spall target. Ablation Compression Wave Shock Velocity: U S Particle Velocity: U P Pressure: P Density: ρ Initial Density: ρ 0 Bulk Sound Speed: c 0 Constant: a Half-wave plate Mirror A pulse stacker is needed so that we can look at a larger time window over which the spallation process occurs. Polarizing Beamsplitter We are using the Z-Beamlet Laser to drive shock waves. Rarefaction wave from reflection of shock from back surface Rarefaction wave from decrease of drive pulse Spall Z-Beamlet is a Nd:Glass laser with a multi-pass amplifier design. Energy: 1.2 kJ at 527 nm Pulse Length: ns Beam Profile: Square and Top-Hat Spot Size for Experiments: 2 mm-10 mm Line-VISAR and 2D Reflectivity/Interferometry are being fielded at Z-Beamlet to test Aluminum. VISAR probe beam: 532 nm, 8 ns FWHM, ~5 mJ Reflectivity/Interferometry probe beam: 1054 nm, 500 fs, ~10 mJ Time Position Time Position No spall signal Result from non-uniform beam