Thesis

Technology development for a compact rubidium optical frequency reference

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Creator
Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2023
Thesis identifier
  • T16735
Person Identifier (Local)
  • 201956716
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • The precision and accuracy of navigation and radar systems is typically limited by the stability of their internal frequency references. Currently, microwave atomic frequency references are close to the limits of what they can achieve in terms of short term stability. Optical atomic frequency references have demonstrated several orders of magnitude improvement in both short-term as well as long-term stability. In the past decade, improvements in optical frequency comb (OFC) technology have enabled the precise measurement of optical frequencies with much smaller form-factors, spurring research to build a portable optical atomic clock referenced to the 87Rb 5S1=2; F = 2 ! 5D5=2; F0 = 4 two-photon transition (TPT). Using a single laser source and simple Doppler-free spectroscopy in a heated Rb vapour cell one can generate an atomic reference signal with a linewidth approaching 334 kHz. The research presented here, compares the suitability of a telecoms (1550-1560 nm) CW laser with a narrow bandwidth OFC laser of 10-20 modes spaced apart at 3-6 GHz frep. The OFC laser achieves more than double the second harmonic conversion effciency compared with the CW laser, while delivering up to 30 mW of 778 nm light. The 778 nm OFC is then used to excite the reference transition and demonstrate coherent interaction of all OFC modes. Towards the aim of making the system compact, the research explores the use of micro-fabricated vapour cells, 3D printed oven designs and a chip-scale DFB (distributed feedback) laser with the prospects of integrating both the laser and spectroscopy on to a single micro-fabricated semiconductor platform. Pre-stabilising a noisy laser to an optical cavity is commonly required for optical atomic clocks, in order to resolve narrow-linewidth transitions. Towards this application, a low-drift, all-metal optical cavity is developed and characterised using Allvar metal, which possesses a negative coecient of thermal expansion (CTE). The overall cavity CTE can be temperature tuned to yield a CTE of < 0.001 ppm/°C at 27 °C. The long-term cavity mode stability of the cavity was measured while referenced to one of the 87Rb 5S1=2 ! 5P3=2 780 nm transitions, residual drifts of 0.3 MHz/hr on time-scales up to 5 hrs (after subtracting o pressure-correlated frequency shifts). The all-metal cavity should be less sensitive to thermal gradients as well as more responsive temperature stabilisation than ultra-low expansion cavities.
Advisor / supervisor
  • Griffin, Paul
  • Riis, Erling
Resource Type
DOI

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file details PDF of thesis T16735 2023-10-17 Public Télécharger