Mid-IR Ultrafast Laser Inscribed Waveguides and Devices

Abstract

MID-IR ULTRAFAST LASER INSCRIBED WAVEGUIDES AND DEVICES Name: McDaniel, Sean A. University of Dayton Advisor: Dr. Gary Cook Ultrafast laser inscription (ULI) is a highly versatile technique for creating index modifications in glasses and crystalline materials. The process of ULI relies on ultrashort laser pulses focused inside of a material. The high intensity of the pulsed beam induces nonlinear absorption processes, which transfers the pulse energy to the material lattice. With careful experimental control of the laser parameters, a permanent change in the refractive can be obtained in the bulk material. The permanent refractive index change obtained by ULI can be used to create waveguides in active laser materials, such as Cr:ZnSe, Fe:ZnSe and Ho:YAG.Transition metal and rare-earth laser sources have been shown to operate over the 2 − 5 µm range. ULI can be used in conjunction with these materials to produce high power, guided-wave structures with reduced size, weight and power (SWaP) requirements. Power levels for Cr:ZnSe and Fe:ZnSe have been scaled to > 5 W and > 1 W respectively in ULI waveguide devices.Additionally, the first Ho:YAG ULI laser has been investigated, exhibiting output powers of ≈ 2 W .In addition to these advances, the theoretical limit for transition metal waveguide lasers was investigated. Transition metal lasers are highly sensitive to the operating temperature of the laser device. If the temperature increase induced in the sample is too high, phonon assisted transitions iii become dominant, thus decreasing the performance of the laser. Laser rate-equations and a thermal model for ULI waveguides were developed to establish a theoretical limit to ULI waveguide operation.Finally, several advancements were made with respect to creating ULI waveguides. An algorithm was developed for creating arbitrary ULI structures from computer generated models. The ability to create arbitrarily generated structures provides the ability to create complex structures using ULI, such as splitters, couplers, and photonic lanterns. Furthermore, a new helical inscription technique was devised for creating smooth index profiles and for creating Bragg structuring. iv ACKNOWLEDGMENTS