A selection of commercially available high-power optical fibres have been characterised for radiation susceptibility in
Sandia’s Annular Core Research Reactor (ACRR). The fibres were subjected to a total gamma and neutron dose >2 Mrad(Si)
in a 7 ms pulse. The neutron fluence was >10<sup>15 </sup> n/cm<sup>2</sup>. Changes in the transmission characteristics of optical fibres carrying
high energy, short duration laser pulses (power densities of around 1.5 GW/cm<sup>2</sup>) were measured.
All fibres survived at least two consecutive radiation exposures, showing typical transient transmission losses of around 20%.
Post radiation exposure, the transmission characteristics returned to those of pristine fibres within one minute.
Direct Optical Initiation (DOI), uses a moderate energy Q-switched Nd:YAG laser to shock initiate secondary
explosives, via either a flyer plate or exploding metal foil. DOI offers significant performance and safety advantages over
conventional electrical initiation. Optical fibers are used to transport the optical energy from the laser to the explosive
Energy densities in the region of 35 J cm<sup>-2</sup> are required for initiation, significantly above the damage threshold of typical
optical fibers. Laser-induced damage is typically caused by laser absorption at the input face due to imperfections in the
surface polishing. To successfully transmit energy densities for DOI, a high quality fiber end face finish is required.
Fiber assemblies were prepared by C Technologies Inc, NJ, USA, with Innovaquartz FG365UEC optical fiber, using a
variety of polishing methods, with both steel and zirconia ferrules. The quality of the fiber end faces was assessed using
non-contact optical profilometry. The damage threshold for each polishing method was then determined using a Q-switched
Nd:YAG laser and the optimal polishing method determined for each ferrule material. Significant performance
differences between zirconia and steel ferrules were observed, and a physical cause of this difference is proposed.
High power laser systems have a number of uses in a variety of scientific and defense applications, for example laser
induced breakdown spectroscopy (LIBS) or laser-triggered switches. In general, high power optical fibers are used to
deliver the laser energy from the source to the target in preference to free space beams. In certain cases, such as nuclear
reactors, these optical systems are expected to operate in ionizing radiation environments. In this paper, a variety of
modern, currently available commercial off-the-shelf (COTS) optical fiber designs have been assessed for successful
operation in the transient gamma radiation environment produced by the HERMES III accelerator at Sandia National
The performance of these fibers was evaluated for high (~1 MW) and low (<1 W) optical power transmission during
high dose rate, high total dose gamma irradiation. A significant reduction in low optical power transmission to 32% of
maximum was observed for low OH- content fibers, and 35% of maximum for high OH- fibers. The high OH- fibers were
observed to recover to 80% transmission within 1 μs and 100% transmission within 1 ms. High optical power
transmission losses followed generally similar trends to the low optical power transmission losses, though evidence for
an optical power dependent recovery was observed. For 10-20 mJ, 15 ns laser pulses, around 46% was transmitted
coincident with the radiation pulse, recovering to 70% transmission within 40 ns of the radiation pulse.
All fibers were observed to completely recover within a few minutes for high optical powers. High optical power
densities in excess of 1 GW/cm<sup>2</sup>
were successfully transmitted during the period of highest loss without any observed
damage to the optical fibers.
A variety of optical systems use high optical powers or energies, for example, power transport. These systems may be expected to operate in harsh and challenging environments, which may include ionizing radiation. In this paper, several different types of modern, commercially available optical fiber designs have been assessed for reliable operation in a transient gamma radiation environment. The fibers tested are large core multimode silica fibers optimized for the delivery of high power infrared laser light. Some of the fibers are specifically designed to operate in harsh radiation environments, and these are compared against designs of varying radiation resilience from other manufacturers. It was found that fibers were able to successfully transmit a laser pulse of up to 0.375 MW in peak power within a few hundred nanoseconds after irradiation, with less than a 10% loss in transmission.
Laser initiation of energetic materials has been a topic of interest almost since the invention of the first laser in 1960.
Since then, a wide range of lasers, and an even wider range of energetic materials, ranging from sensitive primary
explosives such as lead azide, to very insensitive explosives such as Triamino Trinitrobenzene (TATB) have been
investigated. With the continuous reduction in laser size, and increase in laser energies and powers, using lasers to
initiate energetic materials is becoming easier and more practical to implement in a system environment.
In this paper we examine the development of the concept of laser initiation, from its early days using large Ruby lasers,
to the more modern use of Nd:YAG lasers. We collate and present here the open source literature published in this field
in order to produce a concise and accurate historical overview of the research published to date, and make a prediction of
future trends where possible. We also examine research presented in enabling technologies, such as laser-driven flyer
plates and high-energy optical fibers.