Optical processes and laser dynamics in holmium and neodymium upconversion-pumped visible and ultraviolet fluorozirconate fiber lasers

Upconversion-pumped, rare-earth-doped fluorozirconate glass fiber lasers are of interest because of their potential as compact visible or ultraviolet laser sources. This thesis describes studies of three upconversion-pumped fluorozirconate fiber lasers: a Ho3+ 550 nm laser pumped at 645 nm, and two Nd3+ lasers operating at 381 and 412 nm, both pumped at 590 nm.; Spectroscopic studies of the Ho3+ system presented in this thesis were aimed at identifying the processes involved in the upconversion-pumping process. Absorption spectra of Ho3+-doped fluorozirconate glass and emission spectra of Ho3+-doped fluorozirconate bulk glass and fiber obtained using various pump schemes have been used to identify the levels involved and to calculate the transition strengths between the levels. Absorption and emission cross-section spectra for several transitions have been calculated. The holmium fiber laser has been characterized extensively. The dependence of fiber laser performance on fiber length, fiber core size and cavity output coupling is reported. In addition, the wavelength tuning, pump wavelength dependence, and transient characteristics have been explored. Examination of the transient behavior of the laser shows a sustained periodic (∼25 kHz) oscillation in the output power due to competition between transitions originating from the 5F4 level and those originating from the 5S2 level. Excited state absorption near 550 nm from the 5F4 and 5S2 manifolds has been observed. A computational model has been developed to predict the behavior of the continuous wave operation of the holmium fiber laser. The first demonstration of diodepumping of this laser is reported.; The 381 nm upconversion-pumped fiber laser described in this thesis is the first ultraviolet fiber laser to be pumped by any means. Characteristics of this laser and the 412 nm laser, such as the laser excitation spectrum, transient behavior and laser emission spectrum, are described. Upconversion-pumped spontaneous emission from the high lying (38,800 cm-1 above ground) 2F(2)5/2 level is reported for the first time. Several upconversion pumping schemes involving single or dual pump wavelengths are described.