1. Novel Pyrotechnic Compositions for Pyrotechnically-Pumped Lasers
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Novel Pyrotechnic Compositions for Pyrotechnically-Pumped Lasers
Valerian Kuznetsov, Kenneth Smit, and Dmitrii Stepanov
Weapons and Combat Systems Division
PARARI 2019 Technical Brief

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Why lasers ?
Countermeasure against optical sensors
Destruction of drones
Getty Images

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Motivation
Pyrotechnics as a high energy storage
2 orders of magnitude better size, weigh, and power (SWaP) as compared to electrical battery
Ragone plot: power/energy trade-off
our pyrotechnics
is here
J. Phys. Chem. Lett. 2015

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Prior art
First pyro-laser (1963)
Zr/KClO4 powder
lasing
no lasing
C.L. Smith, P.J. Kisatsky, “An investigation into the
feasibility of a pyrotechnic laser pump”, Picatinny Arsenal Technical Report 3102 (1963)

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Prior art
Missile laser guidance & fuzing subsystem
Zr/O2 commercial flash Sylvania Blue Dot Type 600
Nd:Cr:GSGG lasing rod
30 mJ/pulse (3 J total estimated)
“Miniature laser direct-detection radar”,
SPIE Vol Laser Radar VII (1992),
Schwarz EO & Eglin AFB

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Prior art
Soviet space pistol (1984)
Zr and O2 cartridge
1 – 10 J energy output (air rifle), or 1 kW
a bunch of Nd:glass fibres as the lasing media
A.Zak, “The Soviet Laser Space Pistol, Revealed”,
Popular Mechanics, 14 June 2018

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Prior art
Nd:YAG
Latest report on pyro-laser
0.1 g of Zr/KClO4,
Output 0.7 J
Yang etc, “Laser emission from flash ignition of Zr/Al nanoparticles”,
Vol. 25, No. 20 | 2 Oct 2017 | OPTICS EXPRESS -- China

8. Challenges in pyrotechnic pumping
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Challenges in pyrotechnic pumping
Pyrotechnics generally have low radiant exitance (emitted power per area) compared to that of the electrical flash lamp.
focussing of the diffuse light from burning pyrotechnics is impossible – wrap pyrotechnic material around the lasing rod
Intensity of blackbody radiation is proportional to T4.
use a 5000K blackbody or spectrally selective emitter of equal exitance
Temporal and spatial uniformity of pumping irradiation is critical to maximise the pump intensity and its efficiency.
use hot wire / photoflash / low power ignition laser for simultaneous and uniform initiationdistribute the pumping source along the lasing media

9. Intensity of blackbody radiation
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Intensity of blackbody radiation
Nd pump bands:
540 nm ±10 nm
590 nm ±10 nm
750 nm ±10 nm
808 nm ±10 nm
869 nm ±10 nm Zr Mg
IZr/IMg ≈ 4 at 540 nm
IZr/IMg ≈ 3 at 750 nm

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Selective emitter
Nd pump bands:
540 nm ±10 nm
590 nm ±10 nm
750 nm ±10 nm
808 nm ±10 nm
869 nm ±10 nm
Nd pump bands:
540 nm
590 nm
750 nm
808 nm
869 nm
Proposed: B/Ba(NO3)2
Less wasted heat means an increased pumping efficiency

11. Test for spectrometry and combustion duration
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Test for spectrometry and combustion duration

12. Test for spectrometry and combustion duration
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Test for spectrometry and combustion duration
A rig to measure intensity of light from pyrotechnics
pyrotechnic composition
spectrometer probe
photodetector in housing (721 – 875 nm)

13. Test bed -- configuration
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Test bed -- configuration
photodetector
flash from combusting pyrotechnic
pyrotechnic film
glass window
laser rod
pump light
laser light
cover
breadboard
Pyrotechnically-pumped Nd:YAG laser

14. Test bed -- configuration
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Test bed -- configuration
Pyrotechnically-pumped Nd: YAG laser
laser cavity
covered by
pyrotechnics
powder holder
laser output
detector
beam splitter and
He-Ne laser for
cavity adjustment
mirrors

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Laser pump chamber
Bottom reflector of pumping chamber
Lasing rod
Combustion chamber above
pumping chamber
Pyrotechnics on top of lasing rod

16. Pyrotechnic compositions tried
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Pyrotechnic compositions tried
Pyrofilm* B/Ba(NO3)2/PVC
Pyrofilm* with layers of Al/KClO4/Ba(NO3)2, B/Ba(NO3)2, and PVC
powder B/Ba(NO3)2
powder B/KClO4
powder Al/Ba(NO3)2/KClO4
powder, two layers Al/KClO4/Ba(NO3)2 + B/Ba(NO3)2 (sample shown below)
powder Al/Ba(NO3)2/KClO4 + nano-Al/CuO
ignition
Al/KClO4/Ba(NO3)2 layer (0.05 g)
B/Ba(NO3)2 layer (0.05 g)
glass
light
photodetector
* Ken Smit, DST-developed thin-film pyrotechnics

17. Nano-energetic materials
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Nano-energetic materials
Physics:
At nano-scale, stable materials turn combustible due to quantum size effect
CuO, nm
Al, nm
Substrate
Structure of nano-energetic materials
Metal‐oxide systems : Al/CuO, Al/MoO3, Al/Fe2O3, Al/Bi2O3
Metal‐metal composites: Al/Ni, Al/Ti, Ti/B, Zr/B…
Reference:
N.A. Manesh et al, Combustion and Flame, 157(2010)
M. Petrantoni et al, J Appl Phys 108 (2010) 3)
4) C. Rossi et al, J. MicroElectroMechanical systems, V 16, No 4, 2004
Adapted from presentation
by Weitang Li (DST, Research
Engineering)

18. Output of pyrotechnic compositions
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Output of pyrotechnic compositions
Pyrotechnics (0.07 – 0.1 g)
Emission duration
(FWHM)
Output intensity
(721 – 875nm)
Xe electronic flashlamp
1 ms
1.5 V
Mg flash Meggaflash PF300
20 ms
0.35 V
Pyrofilm B/Ba(NO3)2/PVC
200 ms
0.007 V
powder B/Ba(NO3)2
300 ms
0.014 V
powder Al/Ba(NO3)2/KClO4
5 ms
0.12 V
powder Al/KClO4/Ba(NO3)2 + B/Ba(NO3)2
6 ms
0.07 V
powder Al/Ba(NO3)2/KClO4 + nano-Al/CuO
4 ms
0.5 V
table of the pyrotechnics tried, and achieved intensities
The best energy output (duration × intensity) in NIR is from Al/Ba(NO3)2/KClO4 (US photoflash), with addition of 5% of nano-Al/CuO (nanothermite)

19. Test bed – tests performed
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Test bed – tests performed
Nd:YAG laser pyrotechnically pumped by emission from burning 0.1 g of
Al/Ba(NO3)2/KClO4
pumping light
laser output
4.5 ms
Laser is optimised for lowest pumping threshold

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Laser output
The laser emitted energy depending on the mass of the combusted
Al/Ba(NO3)2/KClO4 ‘photoflash’ pyrotechnics. The slope is 0.3 mJ/g; the lasing
threshold is 0.08 g
lasing

21. Emission spectrum of pyrotechnics
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Emission spectrum of pyrotechnics
The emission spectrum from burning 0.1 g of the photoflash pyrotechnics which resulted in 100 mV laser output signal
The emission spectrum from burning 0.1 g of the photoflash pyrotechnics with added g of nano-thermite Al/CuO which resulted in 700 mV laser output signal.

22. Emission spectrum of pyrotechnics
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Emission spectrum of pyrotechnics
The emission spectrum of 0.1 g of the photoflash that pumps the laser
potassium doublet
766 nm
769 nm
500 nm
1000 nm

23. Opportunities to increase intensity
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Opportunities to increase intensity
Selective emitters (Rb, Cs, K, BaO)
Confinement (to increase burning rate)
Cr sensitization of Nd:YAG (to increase absorbance at visible wavelengths)
Nd: glass (to broaden absorption lines)
Increase surface area between burning pyrotechnic and lasing medium (e.g. use fibre(s) as rod(s))
Optimise ignition method (e.g. by using a hot wire)
Use metamaterials

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Conclusion
A Nd:YAG lasing medium was successfully pumped by light emission from burning pyrotechnics consisting of aluminium, potassium perchlorate, and barium nitrate.
Contrary to the prevailing state of the art utilising zirconium-based pyrotechnics with its high radiosity due to high-temperature blackbody radiation, this work utilised aluminium-based pyrotechnics where laser pumping into the 750 nm absorption band of the Nd:YAG crystal was demonstrated using potassium spectral line emission at 760–775 nm.
The observed laser efficiency was low, 0.3 mJ/g, however adding 5% of nanothermite to pyrotechnics resulted in x7 increase of laser power output.