Dual Use Development of Laser Technology

Recent advances in multi-kilowatt semiconductor laser arrays have pushed solid-state laser output power into the KW range. Unfortunately, the output beam quality of diode-pumped solid-state lasers using Nd:YAG and Yb:YAG bulk crystals degrades with increasing pump power and is basically limited by the thermal induced effects inside the non-linear lasing rods. To some extent, good beam quality can be maintained by distributing the pump power uniformly inside the crystal. Even then thermal lensing or self- focusing could still occur, initiating from localized inhomogeneities. To eliminate this serious problem, this proposal introduces a novel concept for establishing a uniform distribution of pump power by using a multicore fiber bundle from which phase-locking can be obtained to emit a single central beam spot with very high brightness as a result of a strong coupling of the evanescent waves inside the cladding.Recently, the output power in the range from 30 to 50W has been achieved by diode-pumping of a single core Nd-doped or Yb-doped fiber laser. To increase the power delivery from these fiber lasers, this proposal describes a laser system consisting of a 2-D phase-locked fiber bundle, uniquely configured in a 2-D staggered array in a common cladding with a specified intercore spacing between two adjacent fibers, so that the multicore system is phase-locked in unit-phase to emit the desired fundamental supermode. By using co-doping technology, very high power in excess of one kilowatt can be achieved with Yb:Er codoped multicore fiber bundle emitting at an eye-safe wavelength. In Phase I, an in-depth study will be conducted to assess potential dual-use of the selected laser technology. Also, a detailed design analysis will be conducted to determine critical parameters required to fabricate the selected laser. In addition, a novel packaging concept for the multicore fiber bundle will be attempted and experimentally verified. The results will be used as the basic guideline for developing a prototype to be demonstrated in Phase II.