#### Research Interests – **Precision Ultraviolet Spectroscopy **

My research focuses on the spectroscopy of simple atoms and the short-wavelength laser sources needed for such experiments. The study of simple atoms – namely hydrogen – has historically been an extremely fruitful endeavor, catalyzing the development of quantum mechanics, quantum electrodynamics and even some nuclear physics. All of these advances occurred when discrepancies were found between the physical theories describing the atomic energy levels and the experimental data. In fact, such discrepancies persist until today (http://arxiv.org/pdf/1301.0905v2.pdf), which may be evidence of physics beyond the standard model.

A major part of our research effort will be the development of lasers with extremely precise frequencies. In fact, to perform competitive spectroscopic measurements, we will need to measure and control our laser frequency with 15 digits of precision (Parthey *et al.,* PRL **107**, 203001 (2011)). However, the precision of such an advanced laser source will not be transferred to an experimental measurement if the motion of the atoms is not well controlled. Therefore, we will also investigate laser cooling of atomic hydrogen, which will require somewhat less precise but very high-power UV lasers.

#### Selected Publications

*Efficient output coupling of intracavity high-harmonic generation*, D.C. Yost, T.R. Schibli and J. Ye., Opt. Lett. **33**, 1099 (2008).

*Optical frequency comb with submillihertz linewidth and more than 10 W average power*, T.R. Schibli, I. Hartl, D.C. Yost, M.J. Martin, A. Marcinkevicius, M.E. Fermann and J. Ye., Nat. Phot. **2**, 355 (2008).

*Vacuum ultraviolet frequency combs from below-threshold harmonics*, D.C. Yost, T.R. Schibli, J. Ye, J.L. Tate, J. Hostetter, M.B. Gaarde and K.J. Schafer. Nat. Phys. **5**, 815 (2009).

*Direct frequency comb spectroscopy in the extreme ultraviolet*, A. Cingöz, D. C. Yost, T. K. Allison, A. Ruehl, M. E. Fermann, I. Hartl and J. Ye, Nature **482**, 68–71 (2011).

*Frequency-comb spectroscopy of the hydrogen 1S-3S and 1S-3D transitions*, E. Peters, D. C. Yost, A. Matveev, T. W. Hänsch and Th. Udem, Ann. Phys.** 525**, L29 (2013).

*Quantum interference in two-photon frequency-comb spectroscopy*, D. C. Yost, A. Matveev, E. Peters, A. Beyer, T. W. Hänsch, and Th. Udem, Phys. Rev. A **90**, 012512 (2014).