A Fully Crystalline Cryogenic Reference Cavity

Kedar, Dhruv

Graduate Thesis Or Dissertation

A Fully Crystalline Cryogenic Reference Cavity Público Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/c821gm41n

Abstract

To date, neutral atom optical lattice clocks have demonstrated the highest precision measurements of fractional frequency shifts. Frequency noise of the optical local oscillator, used to drive the clock transition, is the primary limitation for how quickly these clocks can measure a quantity. Improving the stability of these oscillators is therefore crucial in enabling efficient characterization of physics at smaller energy scales. State-of-the-art optical oscillators employing cryogenic reference cavities have been used to push this frontier, enabling record-level stabilities and precision of neutral atom optical clocks. The exceptional stability of these oscillators has resulted in foundational advances in optical frequency metrology, establishing these systems as worthy scientific pursuits in expanding the role of measurement science.

The fundamental performance of cryogenic cavities utilizing crystalline spacers and substrates has been limited by the Brownian thermal noise associated with mechanical dissipation of the mirror coatings. Recently, crystalline Al1−xGaxAs/GaAs coatings have emerged as a promising candidate for reduced coating thermal noise. We present measurements of the frequency noise of a fully crystalline cryogenic reference cavity with Al0.92Ga0.08As/GaAs optical coatings.

We report on previously unmeasured birefringent noise of crystalline coatings associated with anti-correlated frequency fluctuations between the two polarization modes of the cavity, and identify variables that affect its magnitude. We present phenomenological characterizations of this noise and implement an interrogation scheme that cancels it by simultaneous probing of both polarization modes. These results challenge our current understanding of noise processes generating length fluctuations and introduce our discovery of novel light induced frequency noise.

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