A picosecond visible optical parametric oscillator as a tool for nonlinear spectroscopy

We are characterizing the nonlinear optical properties of materials exposed to high intensity laser pulses for potential applications in sensor protection devices and all-optical switches. Much of the past research in this area has been performed at a few fixed wavelengths which inhibits our ability to model and therefore understand these interactions. This research came from our desire to extend our capabilities in wavelength coverage. Therefore we designed and built a picosecond pulsed source tunable from 420nm to 680nm. Specifically, we designed, constructed and characterized a visible, picosecond, walkoff-compensated optical parametric oscillator (OPO) pumped by the third harmonic of a flashlamp pumped 10Hz Nd:YAG laser. After system characterization, it was used to measure the singlet excited state absorption and refraction cross sections of organic dyes and the ;The experimental results revealed some important information about the energy levels of the class of organic dyes known as porphyrins. These experiments also gave evidence that the OPO output had a temporal modulation which may be caused by the short pump train. This prompted deeper investigation into the behavior and properties of short pump train synchronously pumped OPO's which in turn led us to a redesign which narrowed the spectrum. To bring the entire research effort to fruition required design and engineering work on OPO's, measurements of nonlinear materials properties and data analysis which utilized many theoretical studies and calculations based on previous theories. This work resulted in a novel design for a new class of OPO's. The lessons learned about this picosecond source also helped us learn about nonlinear materials such as excited state absorption in organic dyes. We believe that the increased understanding obtained on short pulse train pumped OPO's will allow others to further refine this class of device.