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

United States Patent

June 3, 2014
View the Complete Patent at the US Patent & Trademark Office
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.sup.2, 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 .mu.m core and a 660 .mu.m cladding was found to be close to single mode, with an M.sup.2=1.6. Another thick cladding fiber (400 .mu.m core and 720 .mu.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 >100 GW/cm.sup.2), wherein the energy in the core was <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 (>20 mJ delivered for 50 ns pulses) without damaging the silica fiber.
Yalin; Azer P. (Fort Collins, CO), Joshi; Sachin (Fort Collins, CO)
Colorado State University Research Foundation (Fort Collins, CO)
13/ 218,263
August 25, 2011
STATEMENT REGARDING FEDERAL RIGHTS This invention was made with government support under Contract No. DE-FC26-01CH11079 awarded by the U.S. Department of Energy. The government has certain rights in the invention.