New Architectures for High Brightness Laser Emission: Thulium Lasers and Raman Lasers in Fiber and Diamond

Thanks to their high beam quality, compactness, and simplicity, the development of ytterbium fiber lasers has dominated the field of Directed Energy (DE) and high brightness continuous wave (CW) lasers in general for the last 10 years. This work has produced many 10\u27s of kilowatts diffraction limited emission by way of spectral or coherent beam combining of many individual channels. However, as the need arises for even higher power deployable systems, on the order of 100\u27s of kilowatts, the appearance of the Transverse Mode Instability (TMI) appears to be a limiting factor. In addition, the danger to bystanders in the usually uncontrollable environment associated with directed energy demands considerations for eye-safety in any such system. In order to circumvent the apparent limitations for power scaling in ytterbium doped lasers, as well as to access the desirable retina-safe regime beyond 1.4 µm, new technology is needed. This dissertation focuses on three such technologies: thulium lasers, Raman fiber lasers, and diamond Raman lasers. Power scaling concepts for thulium doped fiber lasers are introduced, as they access the 2 µm transmission band in atmosphere and are expected to exhibit a much higher TMI threshold than ytterbium. A new architecture of thulium lasers is presented which facilitates novel laboratory studies on thermal blooming by precision wavelength tuning of a narrow linewidth 2 µm laser signal. These studies are expected to be critical in the eventual deployment of extremely high-power ytterbium and thulium based systems. Raman fiber lasers are explored in detail, as they both increase the range of available wavelengths and may surpass ytterbium in terms of ultimate power scalability. Several methods for defeating the ubiquitous brightness enhancement limitations in Raman fiber lasers are employed in graded-index fiber. In addition, a nearly diffraction limited cladding-pumped Raman laser is designed and executed with 10s of kW of peak power. Finally, a broad practical design space for Diamond Raman lasers (DRLs) is simulated. Though a free space laser source, DRLs have high diffraction limited scaling potential as the limitations posed by thermal lensing are lower for diamond than any other known material. With the potential to produce high energy in both the 1.24 µm and 1.5 µm transmission bands in compact and even portable systems, diamond is a promising path to entirely new regimes in laser science. The current scaling efforts in pulsed and CW diamond Raman lasers are introduced, along with a detailed model on a diamond Raman amplifier configuration