Dr. Michael Chini


High-order harmonics from bulk solids were first observed in 2011 by focusing an intense mid-infrared laser through a bulk crystal and detecting the harmonics in a transmission geometry. Due to birefringence and possible nonlinear effects in bulk crystal, the polarization state of the laser can change as it propagates through the crystal in this transmission geometry. This can result in harmonic signal generated with an unknown polarization of light, disrupting the signal. Alternatives to bulk crystal, such as a reflection geometry or thin films, are not always ideal – reflection geometry can introduce nonlinear reflection coefficients, while crystalline thin films can be difficult to produce and are not available for all materials. We propose Jones calculus as a new method to analyze high-order harmonics from bulk solids in a transmission geometry. We predict the laser’s polarization changes due to propagation through a bulk crystal and we show that these changes can be accounted for using a combination of wave plates. Our results indicate that linear birefringence dominates the polarization change in bulk ZnO crystals driven in the mid-IR, which allows us to neglect the effect of nonlinear propagation effects on the polarization state. After compensating for the birefringence, we observe ellipticity-dependent, rotationally sensitive features in the harmonic signal which differ from those observed in previous transmission-geometry experiments. This method increases confidence in and control of HHG measurements in bulk crystal.

About the Author

Erin Crites graduated with honors from the University of Central Florida with a bachelors in Physics and a minor in Mathematics. She was involved in research for several years at UCF, and is continuing to do research as a graduate student at North Carolina State University.

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