Abstract
This study examines the use of the recently developed hollow core kagome lattice fibers for delivery of high power laser pulses. Compared to other photonic crystal fibers (PCFs), the hollow core kagome fibers have larger core diameter (~50 µm), which allows for higher energy coupling in the fiber while also maintaining high beam quality at the output (M2 = 1.25). We have conducted a study of the maximum deliverable energy versus laser pulse duration using a Nd:YAG laser at 1064 nm. Pulse energies as high as 30 mJ were transmitted for 30 ns pulse durations. This represents, to our knowledge; the highest laser pulse energy delivered using PCFs. Two fiber damage mechanisms were identified as damage at the fiber input and damage within the bulk of the fiber. Finally, we have demonstrated fiber delivered laser ignition on a single-cylinder gasoline direct injection engine.
Highlights
Despite nearly 40 years of laser ignition research [1], the technology for safe, reliable and affordable delivery systems is not yet available
Several fiber approaches have been tested for high power pulse delivery for laser ignition including step-index fibers, hollow core fibers, photonic crystal and bandgap fibers
We have identified several mechanisms that can be responsible for this type of damage: laser power fluctuations and beam wander, optical feedback caused by back-reflected light downstream of the fiber, or imperfections/micro-fractures inside the fiber
Summary
Despite nearly 40 years of laser ignition research [1], the technology for safe, reliable and affordable delivery systems is not yet available. Our present research aim is to test and develop an alternative approach for fiber optic delivery of laser pulses (to the engine) using recently developed hollow core kagome lattice photonic crystal fibers (PCFs). The first essential requirement for our Materials 2014, 7 approach is to deliver laser pulses that exceed the minimum ignition energy threshold (~15 mJ per pulse for a typical gas engine) [2,3,4,5]. Several fiber approaches have been tested for high power pulse delivery for laser ignition including step-index fibers, hollow core fibers, photonic crystal and bandgap fibers. Coated hollow fibers have been demonstrated for spark delivery and laser ignition of a gas engine in the past [10,11,12,13]. Hollow core fibers are flexible and have typical inner (hollow) diameters of
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