Scaling infrared femtosecond optical parametric oscillators to high average powers

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2017A demand for ultrafast, highly energetic laser sources in the infrared exists for various applications such as high-harmonic generation, waveguide inscription, and remote sensing. These applications require high repetition rates for faster processing speed and better signal-to-noise ratios. Until recently, laser pulses used in these systems were usually provided by optical parametric oscillators and amplifiers pumped by Ti:sapphire laser systems. The output power and spectral bandwidth of this pump source are fundamentally restricted due to unavoidable limitations caused by the quantum-defect heating and restricted emission spectrum of the gain medium. Advancements to Yb-based sources have provided a significant increase in average power and pulse energy available from ultrafast pumps, thereby increasing the capabilities of parametric devices. In this thesis, an ultrafast optical parametric oscillator was constructed as a test bed for investigating the scaling potential of these devices. The main goals of this study were to utilize recent technological advancements to ultrafast pump sources and test the limits for obtaining high-energy pulses with high average powers from an optical parametric oscillator. Various nonlinear crystals and parametric pumping geometries were investigated to determine how best to use the available power of a home-built pump laser and the general potential for scalability. To utilize recent developments of similar pump sources, a long cavity was designed to take advantage of the high-average-powers with scalable pulse energies. While the designing the cavity, it became apparent that the cavity length could be done easily without notable change to critical cavity parameters by using telescopic imaging relays. It was discovered that limitations to the power scalability of this system were directly linked to problems with the thermal management of the nonlinear crystal. While minor changes could have been implemented to reduce the impact of these boundaries, understanding thermal effects in parametric devices will be critical to fully utilizing the state-of-the-art pump sources. Simple and cost-effective methods were developed for characterizing the impact of the thermal gradient on the available gain. This analysis could easily be extended to other systems for predicting and mitigating thermally induced power scaling limitations