Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session T4: Experimental Developments VIII: Velocity Measurement Techniques 2 |
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Chair: Dayne Fratanduono, Lawrence Livermore National Laboratory Room: Regency Ballroom A |
Thursday, July 13, 2017 11:15AM - 11:30AM |
T4.00001: Line-RALF Doppler Velocimetry Mario Fajardo We report the successful proof-of-concept demonstration of a 1D spatially-dependent variant of our Rubidium Atomic Line Filtered (RALF) Doppler velocimetry technique,$^{\mathrm{1}}$ using streak camera detection of laser light reflected from 1-mm-diameter laser-driven flyers traveling at 1 km/s. RALF employs the frequency-dependent near-resonant optical absorption of a heated Rb/N$_{\mathrm{2}}$ gas cell to convert the Doppler shift of reflected 780.24 nm light directly into transmitted light intensity. This approach results in each individual pixel in a RALF image constituting an independent velocity measurement. RALF advantages over conventional interferometric Doppler velocimetry methods include: a time response limited only by the optoelectronic detection system, and facile adaptation for 1D, and even 2D, imaging velocimetry applications. RALF disadvantages include: the direct conversion of image intensity noise into calculated velocity noise, extreme sensitivity to loss of signal upon shock breakout, and poor tolerance of parasitic reflections of unshifted illumination laser light. 1. M.E. Fajardo, C.D. Molek, and A.L. Vesely, AIP Conf. Proc. \textbf{1793}, 160011 (2017). ``Rubidium Atomic Line Filtered (RALF) Doppler Velocimetry.'' [Preview Abstract] |
Thursday, July 13, 2017 11:30AM - 11:45AM |
T4.00002: Photon Doppler Velocimetry Measurements of Transverse Surface Velocities Christopher R. Johnson, Jeff LaJeunesse, Peter Sable, Ashley Hatzenbihler, John P. Borg Photon Doppler Velocimetry (PDV) is a prominent optical diagnostic used for measuring displacement or velocity in dynamic experiments. A table-top experiment consisting of a 31mm diameter metal wheel mounted in a hand tool was setup to make steady state transverse surface velocity measurements using PDV for a range of velocities and surface preparations. The experiment consisted of PDV collimators positioned with respect to either the side or bottom face of the wheel at various angles to resolve transverse velocity components. Different preparations for the surface of the wheel were explored such as polishing, laser etching, chemical etching, mechanical milling, and retroreflective microspheres. Light return and transverse surface velocity were recorded for each surface preparation as a function of angle. Polished aluminum allowed adequate light return for only one degree from the normal of the wheel, while the retroreflective microspheres exhibited usable light for upwards of 30 degrees. Velocity measurements were performed over a range of 0 to 45 degrees from the surface normal of the rotating wheel for each surface preparation. Velocity measurements from the PDV experiments show good accuracy with theoretical wheel velocities between 0 and 10 m/s. [Preview Abstract] |
Thursday, July 13, 2017 11:45AM - 12:00PM |
T4.00003: VISAR fringe analysis under extreme spatially varying shock loading David Erskine, Dayne Fratanduono Many VISAR velocity interferometers employ a streak camera to record fringes along the spatial axis (Y) of a target, versus time. When the shock loading (thus velocity history) varies rapidly versus Y, the fringe analysis challenges traditional algorithms since the Y-spacing of fringes can vary strongly with Y, and be significantly different than the uniform pre-shock (bias) spacing. For traditional colum-by-column analysis the intensity signal shape would be a sinusoid with rapidly varying frequency (chirped), which can confuse a traditional algorithm expecting a monochromatic peak in Fourier space. And for a traditional push-pull row-by-row approach, the phase steps are irregular. We describe preliminary success in analyzing such data in simulation. We find it useful to (a) separate the nonfringing component from the data early; (b) maximize linearity of a plot of fringing magnitude versus nonfringing intensity to choose optimal weight values; (c) when using a row-by-row approach sampling 0, 90, 180, and 270 degrees phase we add a fifth sample at 360 degrees, which is averaged with the 0 degree sample and replaces it. This increases the robustness to variable phase step (following P. Hariharan). The pre-shock and post-shock regions are separately processed/concatenated. [Preview Abstract] |
Thursday, July 13, 2017 12:00PM - 12:15PM |
T4.00004: Shot Noise and Fiber Amplifier Effects in Photonic-Doppler Velocimetry Systems Edward Kirk Miller, Eric Larson, Kevin Lee We present theoretical and experimental data to show the effects of shot noise and erbium-doped fiber amplifiers (EDFA's) on the achievable dynamic range of photonic-Doppler velocimetry (PDV) systems. We show that many common system configurations are very nearly shot noise limited. Heterodyne gain from strong local-oscillator (LO) light creates a signal amplitude that can be recorded on high-speed digitizers, and the shot noise from the LO sets the system noise floor above the levels of electronic noise in the photoreceiver and digitizer. We show that boosting weak signal returns using an EDFA creates noise in the same proportion that it increases signal, leaving the signal-to-noise ratio (SNR) unchanged. Amplified spontaneous emission (ASE) from the EDFA, when mixed with the LO light, creates a noise term proportional to the LO shot noise and to the EDFA gain. The net result is that EDFA's are useful for boosting heterodyne signal levels for recording, and they can be used to boost weak return light before lossy components, but they do not improve the fundamental SNR of the system. [Preview Abstract] |
Thursday, July 13, 2017 12:15PM - 12:30PM |
T4.00005: A simple and accurate method for shock wave velocity measurement of initially transparent material based on optical reflection Chengjun Li, Qifeng Chen, Yunjun Gu, Jun Zheng, Jiangtao Li, Zhiguo Li Shock velocity (Us) is one of the most important parameters in shock wave experiments. So far, there are various methods of Us measurement for initially transparent sample, such as X-ray radiography, VISAR,and the method of recording optical radiance history (ORH). Recently we have developed an improvedUs measurement method by recording the history of reflected optical signal during the propagation of shock wave in the sample, which was sandwiched between two high impedance materials: baseplate and window. Since the reflection signal jumps abruptly at the interfaces of baseplate/sample and sample/window, the propagating time of the shock wave in the sample can be obtained. Hence, Us is determined with the known thickness of the sample.Applying this method in shock experiments, we have got the Us for different samples. This optical reflection method is more economic and easier to operate than VISAR and X-ray radiography, and has higher time resolution than ORH. Moreover, the method can also be applied for reflectivity measurement of the sample from initially transparent state to opaque under shock compression. [Preview Abstract] |
Thursday, July 13, 2017 12:30PM - 12:45PM |
T4.00006: Development of the symmetrical laser shock test for weak bond inspection. Maxime Sagnard, Laurent Berthe, Romain Ecault, Fabienne Touchard, Michel Boustie This paper presents the LAser Shock Adhesion Test (LASAT) using symmetrical laser shocks. The study is part of ComBoNDT European project that develops new Non-Destructive Tests (NDT) to assess adherence properties of bonded composite structures. This NDT technique relies on the creation of a plasma on both side of the sample using two lasers. The plasma expands and generates shockwaves inside the material. When combined, the shockwaves create a local tensile strength. Properly set, this stress can be used to test interfaces adherence. Numerous experiments have shown that this adaptive technique can discriminate a good bond from a weak one, without damaging the composite structure. Weak bonds are usually created by contaminated surfaces (residues of release agent, finger prints, \textellipsis ) and were artificially recreated for ComBoNDT test samples. Numerical simulations are being developed as well, to improve the comprehension of the physical phenomenon. And ultimately, using these numerical results, one should be able to find the correct laser parameters (intensity, laser spot diameter) to generate the right tensile strength at the desired location. [Preview Abstract] |
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