Outline. Nuclear Forensics & Laser-Induced Breakdown Spectroscopy. Interferometry & Shadowgraphy. Conclusion & Future Work. Experimental Setup

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1 Outline Nuclear Forensics Laser-Induced Breakdown Spectroscopy Interferometry Shadowgraphy Experimental Setup Conclusion Future Work 1

2 Nuclear forensics The analysis of nuclear materials recovered from either the capture of unused nuclear materials, or from the radioactive debris following a nuclear explosion. 2

Sample preparation versus in situ analysis

sensitivity - Destructive - Time consuming -

Rapid + No sample preparation + Stand-off

3 Sample preparation versus in situ analysis for nuclear forensics Chemical separation and sample preparation In situ analysis Collection Sample preparation + High sensitivity - Destructive - Time consuming - Generates toxic waste In situ analysis + Rapid + No sample preparation + Stand-off capabilities - Lower sensitivity Identification and attribution 3

4 Laser-induced breakdown spectroscopy (LIBS) Laser ablation removes a small amount of sample mass by coupling laser energy into the material 1 - plasma generation 2 - light collection 3 - spectral analysis 4 - determine composition 4

time (gate window) are important in optimizing SNR.

5 Spectral features of LIBS signals are time-dependent e- e- e- e- e- Continuum emission E E Emission of discrete atomic lines 1 µs 1 µs LIBS signal Delay time (gate delay) and integration time (gate window) are important in optimizing SNR. 1 ns 10 ns 100 ns 1 µs 10 µs 100 µs Time after laser ablation 5

6 Short-pulse LIBS vs long-pulse LIBS Long pulse: ns Short pulse: ps - fs Nd:YAG laser Ti:sapphire laser 6

7 SNR shows dependence not only on the pulse duration but also on the sign of the chirp K. Hartig, et al., J. Anal. Nucl. Chem. (accepted). 7

8 Outline Nuclear Forensics Laser Induced Breakdown Spectroscopy Interferometry Shadowgraphy Experimental Setup Conclusion Future Work 8

$Surface Refractive index distribution$ $fractional intensity variation of a$ plasma: I I = L d dx 2 + d dy 2 Ndl D.

9 Shadowgraphy LIBS Beam Ambient Air Expanding Plasma Probe Beam Sample Surface Refractive index distribution can be determined by measuring the fractional intensity variation of a probe beam as it travels through the plasma: I I = L d dx 2 + d dy 2 Ndl D. Breitling, et al., Appl. Phys. A 69 [Suppl.], S505 S508 (1999) 9

10 Interferometry CCD Laser LIBS Beam Ambient Air Expanding Plasma Probe Beam Sample Surface 10

$Reconstruction of the refractive index from the 2D interferogram A discrete Abel inversion can be used to extract the refractive index$

11 Reconstruction of the refractive index from the 2D interferogram A discrete Abel inversion can be used to extract the refractive index distribution from the measured interferogram Zhang H., Lu J., Ni X. (2008) Proc. Computer Science and Software 11 Engineering 2(11):

12 Outline Nuclear Forensics Laser Induced Breakdown Spectroscopy Interferometry Shadowgraphy Experimental Setup Conclusion Future Work 12

13 Experimental setup LIBS beam interferometer delay line probe beam fs laser beam splitter focusing lens vacuum chamber collection lens spectral analysis CCD spectrometer Interference Pattern CCD 13

14 Experimental setup LIBS beam interferometer delay line Mach-Zehnder Interferometer probe beam fs laser beam splitter focusing lens vacuum chamber collection lens reference beam spectral analysis CCD spectrometer Interference Pattern CCD 14

15 Key features of the experimental setup 3 ft. delay line provides a temporal range 6 ns with picosecond resolution. 300 mm imaging lens provides 5x magnification fs laser Buffered monochrome 1.3MP CCD camera with 1280x960 resolution, 6.26x5.01 mm field of view beam splitter Vacuum chamber and pressure regulator Ti:Sapphire laser system delay line Mach-Zehnder Interferometer probe beam focusing lens collection lens reference beam CCD spectrometer CCD 15

16 Outline Nuclear Forensics Laser Induced Breakdown Spectroscopy Interferometry Shadowgraphy Experimental Setup Conclusion Future Work 16

17 Future work Apply this technique to plasma generated on the surface of a uranium target Knowledge of plasma density and plasma formation could help improve SNR of LIBS spectrum 17

ability to determine the elemental composition of special nuclear

18 Summary Diagnostic technique for studying the density and formation of laser induced plasmas Improved LIBS signal to noise ratio The ability to determine the elemental composition of special nuclear materials Standoff detection method for nuclear forensics applications 18

High-Accuracy LIBS with Nanosecond and Picosecond Time Resolution Enabled by Ultrasensitive emiccd Technology

2015 Princeton Instruments, Inc. All rights reserved. High-Accuracy LIBS with Nanosecond and Picosecond Time Resolution Enabled by Ultrasensitive emiccd Technology The PI-MAX4:1024EMB emiccd camera seamlessly