Single-mode fibers were cleverly embedded into fixtures holding nitromethane, and used in conjunction with a photonic Doppler velocimeter (PDV) to measure the associated detonation velocity. These measurements have aided us in our understanding of energetic materials and enhanced our diagnostic capabilities.
An optical circulator is a multi-port, nonreciprocal device that routes light from one specific port to another. Optical circulators have at least 3 or 4 ports, up to 6 port possible (JDS Uniphase, Huihong Fiber) Circulators do not disregard backward propagating light, but direct it to another port. Optical circulators are commonly found in bi-directional transmission systems, WDM networks, fiber amplifiers, and optical time domain reflectometers (OTDRs). 3-Port optical circulators are commonly used in PDV systems. 1550 nm laser light is launched into Port 1 and will exit out of Port 2 to the target. Doppler-shifted light off the moving surface is reflected back into Port 2 and exits out of Port 3. Surprisingly, a circulator requires a large number of parts to operate efficiently. Transparent circulators offer higher isolation than those of the reflective style using PBSs. A lower PMD is obtained using birefringent crystals rather than PBSs due to the similar path lengths between e and o rays. Many various circulator designs exist, but all achieve the same non-reciprocal results.
A new laser trigger system (LTS) has been installed on Z that benefits the experimenter with reduced temporal jitter on the x-ray output, the confidence to use command triggers for time sensitive diagnostics and the ability to shape the current pulse at the load. This paper presents work on the pulse shaping aspects of the new LTS. Pulse shaping is possible because the trigger system is based on 36 individual lasers, one per each pulsed power module, instead of a single laser for the entire machine. The firing time of each module can be individually controlled to create an overall waveform that is the linear superposition of all 36 modules. In addition, each module can be set to a long- or short-pulse mode for added flexibility. The current waveform has been stretched from ∼100 ns to ∼250 ns. A circuit model has been developed with BERTHA Code, which contains the independent timing feature of the new LTS to predict and design pulse shapes. The ability to pulse-shape directly benefits isentropic compression experiments (ICE) and equation of state measurements (EOS) for the shock physics programs at Sandia National Laboratories. With the new LTS, the maximum isentropic loading applied to Cu samples 750 um thick has been doubled to 3.2 Mb without generating a shockwave. Macroscopically thick sample of Al, 1.5 mm, have been isentropically compressed to 1.7 Mb. Also, shockless Ti flyer-plates have been launched to 21 km·s-1, remaining in the solid state until impact.
Of special promise for providing dynamic mesoscale response data is the line-imaging VISAR, an instrument for providing spatially resolved velocity histories in dynamic experiments. We have prepared two line-imaging VISAR systems capable of spatial resolution in the 10-20 micron range, at the Z and STAR facilities. We have applied this instrument to selected experiments on a compressed gas gun, chosen to provide initial data for several problems of interest, including: (1) pore-collapse in copper (two variations: 70 micron diameter hole in single-crystal copper) and (2) response of a welded joint in dissimilar materials (Ta, Nb) to ramp loading relative to that of a compression joint. The instrument is capable of resolving details such as the volume and collapse history of a collapsing isolated pore.