This project explores ultra-broad bandwidth generation of optical pulses in the ultraviolet (UV), deep UV, and vacuum UV (VUV) spectral ranges. Conversion of few cycle pulses to the UV has traditionally been limited by dispersion and transparency constraints from dispersive crystals and by inherent low conversion efficiency in low density gases. This work will develop a detailed understanding of the physics of few-cycle light pulses propagating in spatially structured plasmas for optimization of efficient conversion to short wavelength odd-order optical harmonics. Besides investigating new optical physics, these studies will pave the way for the generation of ultra-broad bandwidth pulses compressed to <5-fs in duration in the UV, deep UV, and VUV spectral regions.
Efficient sources of VUV few cycle laser pulses will prove to be an invaluable tool for probing excited state dynamics of molecules and for probing electronic structure of molecules and materials. The ultrafast laser pulses will serve as excellent probes of fast processes such as dynamics at conical intersections, photoisomerization, photodissociation, and photobiology, to name a few. An area where application of these tools is particularly apt is for studying photoconversion processes such as dynamics in light harvesting complexes and electron transfer dynamics and dye sensitized photoconversion cells.
Undergraduate researchers will be included in all aspects of this project, focusing on research areas of short pulse propagation, nonlinear optics, ultrafast optics, plasma physics, and molecular spectroscopy. Involvement by students through summer undergraduate programs (REU, McNair, LSAMP) will encourage students from diverse backgrounds. In addition, the PI will continue revising and delivering his "optics show" for K-2nd graders.
In this project, we investigated the ability to enhance the conversion efficiency of very short laser pulses from the near infrared (NIR) spectral region into the ultraviolet (UV) spectral region. UV laser pulses are difficult to generate. The most successful strategy for generating UV pulses is to convert energy from longer wavelength NIR pulses into UV pulses. We found and explored increased conversion efficiency using spatially localized plasma to generate UV short laser pulses. Numerical models were developed that explained the fundamental mechanism of increased conversion efficiency. The mechanism is due to a temporal walkoff of UV pulsed light generated in the focus of a femtosecond laser pulse in a gas when plasma is present. The group velocity change and rapid index of refraction change from the plasma allows the strong UV light generated at the smallest region of the spatial focus to propagate to the far-field, translating into a high quality spatial beam in the far field. These sources are important for nanoscale optical patterning and for understanding the behavior of molecules in the excited state. Development of this science further advanced our understanding of strong-field laser-matter interactions and ultrafast nonlinear optical science. A graduate student learned plasma physics, ultrafast optical science, and nonlinear optics, and was trained to perform complex scientific investigations.
