Review of Laser Initiation

Abstract

The first experiments with laser initiation of energetic materials as an alternative to standard electrical initiation were performed in the early 1960s. This was a direct consequence of the success of laser beams in cutting through steel and other metal sheets by rapidly melting them. Most of the lasers used were in the red to infrared region, since it was thought that direct heating was the optimum method to achieve the rapid combustion needed for typical propellant ignition. Looking at the scattering of laser radiation in Raman spectrometry, the closer the radiation wavelength is to the molecular vibration frequencies, the stronger the inelastic scattering is, and the more energy is transferred to molecular vibrations; the criteria for an increase in temperature leading to ignition.Later work used lasers to initiate secondary high explosives directly, thus eliminating the need for highly sensitive primary explosives. The experimental arrangement for this study is shown in Figure 2.1. Note the advantage of not having a very sensitive primary explosive, so that the chances of accidental initiation are very much reduced.Laser-initiated field guns started to be tested by the US army in the early 1990s, with the Nd/Glass laser operating at 1.05 μm being the one of choice because of its small dimensions, ruggedness, long life and low cost. The object of these preliminary trials was to initiate the gunpowder booster directly without using the standard, percussion-sensitive military M82 primer. This wavelength was also very adaptable, since it could be transmitted over considerable distances by high purity silica optical fibres, with very little loss due to radiation absorption. Simple use of splitter systems in the optical fibres enabled a number of initiation points to be simultaneously initiated, giving an optimized burn within a single propellant charge. Fibre optic transmission of the laser beam also enabled multiple charges to be initiated simultaneously from a single firing command. This latter has a distinct attraction for quarrying operations if delay detonators can be initiated.A number of prototype guns using laser initiation have been demonstrated in the early 21st century, but regular operation has not been implemented. The Crusader SPH XM2001Laser Ignition of Energetic Materials, First Edition. S Rafi Ahmad and Michael Cartwright.