Author Institution: Lawrence Livermore National LaboratorySlides presented at the 3nd Annual Photonic Doppler Velocimetry (PDV) Conference and Workshop held at Sandia National Laboratories, Albuquerque, New Mexico, September 3-4, 2008

Bonner, Randy

Hester, Daron

Strand, Oliver T.

Whitworth, Tony L.

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Lawrence Livermore National Laboratory Ted Strand, Randy Bonner Daron Hester, Tony Whitworth This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.!Performance Measures x.x, x.x, and x.x!Factors to Consider When!Choosing a Probe for PDV!UNCLASSIFIED!UNCLASSIFIED!LLNL-CONF-xxxxxx!2 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Ouline -- Factors to Consider When Choosing a Probe Factors to consider!!Probe types commonly used at LLNL!!Conclusions!UNCLASSIFIED!UNCLASSIFIED!3 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--initial stand-off UNCLASSIFIED!UNCLASSIFIED!How far do you need!to follow the surface?!!A longer stand-off!allows the probe!to follow the surface!a longer distance.!!This is probably!the single biggest!factor.!Narrow!FWHM!Broad!FWHM!4 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--initial stand-off UNCLASSIFIED!UNCLASSIFIED!Focusing probes have an efficiency curve that limits!the depth of field.!We usually set the initial probe-to-surface distance!with the focal point in front of the surface.!This allows us to follow the surface a longer distance.!5 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration UNCLASSIFIED!UNCLASSIFIED!Factors to consider--initial stand-off Long stand-off probes!allow access for!other diagnostics.!6 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--surface tilt UNCLASSIFIED!UNCLASSIFIED!We will initially install!the probe at an angle!to the surface normal!if we know the surface!will tilt during the!measurement.!!We generally try to stay!within 10 degrees of the !surface normal. We need!a diffuse surface for this!technique.!10 degrees!Place the probe so that the surface normal!sweeps through the probe during the measurement.!7 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--physical space UNCLASSIFIED!UNCLASSIFIED!Short stand-off probes!will not allow!closely-spaced!measurements if we!do not exceed 10 degrees.!8 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--physical space UNCLASSIFIED!UNCLASSIFIED!Smaller diameter probes!will fit into a smaller space!but have lower efficiencies,!which means less signal.!9 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--solid angle UNCLASSIFIED!UNCLASSIFIED!Large!solid!angle!Small!solid!angle!A large solid angle!collects more light,!which means!less laser power!or compensates!for low surface!reflectivity!10 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--solid angle UNCLASSIFIED!UNCLASSIFIED!Large!solid!angle!Small!solid!angle!A large solid angle!allows more tilt!The red rays show the case for a specular surface,!but the same principle applies to a diffuse surface.!11 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--surface preparation UNCLASSIFIED!UNCLASSIFIED!Specular!surface!Diffuse!surface!Specular surfaces generally go diffuse when shocked,!so we often make a diffuse surface initially to avoid!large drops in the signal returned to the probe.!!This also helps with surfaces that tilt during the measurement.!(higher peak brightness)!(bead blast or ball roll)!12 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--spot diameter UNCLASSIFIED!UNCLASSIFIED!desired stand-off!desired stand-off!f!f!Some measurements require high spatial resolution at shock arrival,!which means you want a small spot diameter.!Place the surface at the focal point to start the measurement.!The focal length of the lens affects the spot size.!13 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--power budget The power budget for PDV is sufficient for probes with 10-4 efficiency!2W!Laser! probe!0.85! 0.85!0.85!0.25!0.25!0.25!0.25!0.95! 1 x 10-4!55 µW!1 x 10-4!Detector!2000 V/W!Digitizer!12 GHz!These detectors!saturate at!2 mW!The circulator!has a max power!rating of 0.5 W!We order probes!with BRs to match!the surface return!UNCLASSIFIED!UNCLASSIFIED!Historically, we use probes with 10-4 efficiency!14 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--probe back reflection 2W!Laser! probe!0.85! 0.85!0.85!0.25!0.25!0.25!0.25!0.95!Probe BR =!1 x 10-4!55 µW!We use angled FC connectors!everywhere (-60 dB)!Detector!2000 V/W!Digitizer!12 GHz!UNCLASSIFIED!UNCLASSIFIED!It is important to have only a single source of undoppler-shifted light!We have used probes with BR ranging from 0.04 to 10-4!15 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Factors to consider--probe back reflection LANL uses probes with very low back reflection!and an external variable source of undoppler-shifted light.!Laser!Detector!Digitizer!probe!They order probes!with -60 dB!back reflection!Variable!reflector!10%!90%!UNCLASSIFIED!UNCLASSIFIED!16 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 240-mm focusing probe Oz Optics designed and built a custom probe that matched!the physical dimensions and optical efficiencies of our FP probes!!We quickly realized the advantage of buying probes!!rather than building them!!Initial stand-off is usually 250 mm.!Oz Optics Part # LPF-OSP-1300/1550-9/125-S-8.7-240-25AC-40-3A-3-5!Probe body is!15 mm dia x 40 mm!!Lens dia = 12.5 mm!Focal length = 240 mm!Efficiency = 1.1 x 10-4!BR = -40 dB!Spot dia = 90 µm!UNCLASSIFIED!UNCLASSIFIED!17 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 240-mm focusing probe We use the 240-mm probes for cook-off experiments.!250-mm stand-off keeps the probes outside the heaters.!30 mm!Heater!Probe!0.010.11101001000Velocity (m/s)-300 -200 -100 0Trigger Time (µs) Vp1 Vp2 Vp3Velocity vs TimeUNCLASSIFIED!UNCLASSIFIED!18 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 97-mm focusing probe We use more 97-mm probes than any other size or type.!We usually set the initial distance at 102 mm from the surface.!Probe body is!8 mm dia x 19 mm long!!Lens dia = 5 mm!Focal length = 97 mm!Efficiency = 0.38 x 10-4!BR = -40 dB!Spot dia = 150 µm!Oz Optics Part # LPF-04-1550-9/125-S-15-97-6.2AS-40-3A-3-5!UNCLASSIFIED!UNCLASSIFIED!19 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 97-mm focusing probe probe 1 probe 2 probe 3 probe 4 1400120010008006004002000Velocity (m/s)50403020100Time (µs) vp1 vp2 vp3 vp433 mm!UNCLASSIFIED!UNCLASSIFIED!20 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 5.5-mm focusing probe We sometimes have very small packages that require many probes!Oz Optics Part # LPF-07-1550-9/125-S-5-5.5-1.01GR-15-3A-1-2!Probe body is!1.5 mm dia x 10 mm long!!Lens dia = 1.0 mm!Focal length = 5.5 mm!Efficiency = 4.1 x 10-4!BR = -15 dB (= 4%)!Spot dia = 50 µm!UNCLASSIFIED!UNCLASSIFIED!21 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 5.5-mm focusing probe 25002000150010005000Velocity (m/s)5.65.24.84.4Time (µs)Velocity vs TimeRed = 1-3Blue = 4-6This experiment required 6 measurements within 21 mm!1.0 mm!UNCLASSIFIED!UNCLASSIFIED!22 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 0.5-mm proximity probe A bare fiber makes an effective probe for short-distance measurements!spot diameter!= 150 µm!0.14 NA!0.5 mm!BR = -15 dB = 4%!FC/APC! FC/U!Fiber jumper!A simple fiber connector!makes a quick and!easy probe!UNCLASSIFIED!UNCLASSIFIED!0.5 mm!Efficiency = 0.33 x 10-4!23 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 0.5-mm proximity probe Glue the fibers into different assemblies and polish the ends!0.5 mm!0.5 mm!SST capillary!Multiple fibers!in a “puck”! Individual fibers!glued into holes!UNCLASSIFIED!UNCLASSIFIED!24 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 0.5-mm proximity probe 100 ps!standard deviation!among 7 probes!7 fibers glued!into a puck!Shock arrival measurement!on a gas gun!UNCLASSIFIED!UNCLASSIFIED!25 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration 0.5-mm proximity probe 0.5 mm!SST!capillary!Capillaries are made!by Vita Needle Company!1/16” OD x 0.020” wall thk!Individual fibers!glued into holes!UNCLASSIFIED!UNCLASSIFIED!300025002000150010005000Velocity (m/s)8.58.07.57.06.56.0Digitizer time (µs)Velocity vs Time0.60.50.40.30.20.10.0Distance (mm)8.58.07.57.06.56.0Digitizer time (µs)Distance vs Time26 Option:UCRL#! LL-WCI-U-2007-xxxxxx!Weapons & Complex Integration Summary and Conclusions  Factors to consider include: distance to follow surface, surface tilt,!!physical space, surface preparation, power budget!!We use a wide variety of commercially-available probes for PDV!!240 mm, 97 mm, 5.5 mm!!A bare fiber at a distance of 0.5 mm makes an effective probe!!Focusing probes can usually follow the surface for 15 - 30%!!of the initial probe-to-surface distance!UNCLASSIFIED!UNCLASSIFIED!

Factors to Consider when Choosing a Probe

https://kb.osu.edu/bitstream/1811/52688/1/PDV_2008_Strand_ChoosingProbes.pdf

Factors to Consider when Choosing a Probe

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