We present the results of an LDRD project to develop diagnostics to perform fundamental measurements of material properties during shock compression of condensed phase materials at micron spatial scales and picosecond time scales. The report is structured into three main chapters, which each focus on a different diagnostic devel opment effort. Direct picosecond laser drive is used to introduce shock waves into thin films of energetic and inert materials. The resulting laser - driven shock properties are probed via Ultrafast Time Domain Interferometry (UTDI), which can additionally be used to generate shock Hugoniot data in tabletop experiments. Stimulated Raman scattering (SRS) is developed as a temperature diagnostic. A transient absorption spectroscopy setup has been developed to probe shock - induced changes during shock compressio n. UTDI results are presented under dynamic, direct - laser - drive conditions and shock Hugoniots are estimated for inert polystyrene samples and for the explosive hexanitroazobenzene, with results from both Sandia and Lawrence Livermore presented here. SRS a nd transient absorption diagnostics are demonstrated on static thin - film samples, and paths forward to dynamic experiments are presented.
We present the results of a two year early career LDRD project, which has focused on the development of ultrafast diagnostics to measure temperature, pressure and chemical change during the shock initiation of energetic materials. We compare two single-shot versions of femtosecond rotational CARS to measure nitrogen temperature: chirped-probe-pulse and ps/fs hybrid CARS thermometry. The applicability of measurements to the combustion of energetic materials will be discussed. We have also demonstrated laser shock and particle velocity measurements in thin film explosives using stretched femtosecond laser pulses. We will discuss preliminary results from Al and PETN thin films. Agreement between our results and previous work will be discussed.
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
Kearney, Sean P.; Farrow, Darcie F.; Miller, Joseph D.; Meyer, Terrence R.
We discuss recent experiments and modeling for the chirped-probe-pulse generation of single-laser-shot femtosecond pure-rotational CARS/CSRS spectra from room-temperature gases. A pure-rotational Raman coherence is impulsively generated using near-transform-limited femtosecond pump/Stokes excitation, and the coherence is probed by stretching a nominally 100-fs near-transform-limited probe beam to approximately 1.7 ps via the refractive-index dispersion in a 30-cm long flint-glass rod. The linearly chirped probe spectrum and phase beat against the time-dependent Raman polarization to generate complex spectra. Chirped-probe-pulse rotational CARS/CSRS offers an interesting alternative to hybrid fs/ps rotational CARS, in which a band-limited pulse of limited energy is used, because all of the available probe pulse energy can be retained in a chirped-probe-pulse experiment. Our early chirped-probe spectra are presented and the details of our initial model calculations are provided. The temperature sensitivity of the chirped-probe results is illustrated using calculated spectra.