The extreme ultraviolet (XUV) is a relatively unexplored spectral region for high-resolution laser spectroscopy. Many atomic and molecular systems of fundamental interest lie in wait of investigation, but the lack of highly coherent sources has forgone the ability to experiment. The XUV frequency comb offers exciting new frontiers for fundamental physics and measurement science by enabling direct and highly coherent laser access to the XUV. Prior to 2012, our group demonstrated the best levels of phase coherence in the XUV at the 10 MHz level and the most powerful XUV light source originating from high-order harmonic generation with powers of 220 µW/harmonic. The work in this thesis improves upon both of these metrics demonstrating coherence at the 62.5 mHz level (eight orders of magnitude improvement) and power levels approaching 1 mW/harmonic (five times improvement). Our work shows that it is possible to produce XUV light with coherence properties that rival that of visible light using the high-order harmonic generation process.
Leveraging XUV frequency comb technology, we also extend the work to probe strong field physics in atomic and molecular systems. We use the phase stable light produced during high-order harmonic generation to probe attosecond phenomena in atoms manifested in the intensity dependent dipole phase. We also study strong-field light-matter interactions in molecular systems.
Using our femtosecond enhancement cavities, we perform field-free molecular alignment at unprecedented repetition rates. This allows for a sensitive study of the strong-field interaction and allows the high-order harmonic generation process to be performed in an aligned molecular target.
As XUV frequency comb technology continues to mature, further gains in power levels are anticipated. Additional applications in high-resolution spectroscopy, strong-field physics, solid-state physics, and laser science will come to fruition.