Colorado State University Research Foundation

Sachin Joshi

Azer P Yalin

Bryan Willson

Morgan Defoort

Adam Reynolds

An apparatus and method for transmission of laser pulses with high output beam quality using large core step-index silica optical fibers having thick cladding, are described. The thick cladding suppresses diffusion of modal power to higher order modes at the core-cladding interface, thereby enabling higher beam quality, M, than are observed for large core, thin cladding optical fibers. For a given NA and core size, the thicker the cladding, the better the output beam quality. Mode coupling coefficients, D, has been found to scale approximately as the inverse square of the cladding dimension and the inverse square root of the wavelength. Output from a 2 m long silica optical fiber having a 100 &#x3bc;m core and a 660 &#x3bc;m cladding was found to be close to single mode, with an M=1.6. Another thick cladding fiber (400 &#x3bc;m core and 720 &#x3bc;m clad) was used to transmit 1064 nm pulses of nanosecond duration with high beam quality to form gas sparks at the focused output (focused intensity of &#x3e;100 GW/cm), wherein the energy in the core was &#x3c;6 mJ, and the duration of the laser pulses was about 6 ns. Extending the pulse duration provided the ability to increase the delivered pulse energy (&#x3e;20 mJ delivered for 50 ns pulses) without damaging the silica fiber.

Transmission of laser pulses with high output beam quality using step-index fibers having large cladding

A spark delivery system for generating a spark using a laser beam is provided, and includes a laser light source and a laser delivery assembly. The laser delivery assembly includes a hollow fiber and a launch assembly comprising launch focusing optics to input the laser beam in the hollow fiber. The laser delivery assembly further includes exit focusing optics that demagnify an exit beam of laser light from the hollow fiber, thereby increasing the intensity of the laser beam and creating a spark. Other embodiments use a fiber laser to generate a spark. Embodiments of the present invention may be used to create a spark in an engine. Yet other embodiments include collecting light from the spark or a flame resulting from the spark and conveying the light for diagnostics. Methods of using the spark delivery systems and diagnostic systems are provided.

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Fort Collins, CO, United States of America

Sachin Joshi