Abstract
The temperature stability of optical reference cavities is significant in state-of-the-art ultra-stable narrow-linewidth laser systems. In this paper, the thermal time constant and thermal sensitivity of reference cavities are analyzed when reference cavities respond to environmental perturbations via heat transfer of thermal conduction and thermal radiation separately. The analysis as well as simulation results indicate that a reference cavity enclosed in multiple layers of thermal shields with larger mass, higher thermal capacity and lower emissivity is found to have a larger thermal time constant and thus a smaller sensitivity to environmental temperature perturbations. The design of thermal shields for reference cavities may vary according to experimentally achievable temperature stability and the coefficient of thermal expansion of reference cavities. A temperature fluctuation-induced length instability of reference cavities as low as 6 × 10(-16) on a day timescale can be achieved if a two-layer thermal shield is inserted between a cavity with the coefficient of thermal expansion of 1 × 10(-10) /K and an outer vacuum chamber with temperature fluctuation amplitude of 1 mK and period of 24 hours.
Highlights
Optical reference cavities with finesse of >100,000 are widely used to stabilize the frequency of lasers in optical atomic clocks, precision metrology, high resolution spectroscopy, tests of fundamental physics and deep space navigation [1,2,3,4,5,6,7], which rely on the high frequency stability of lasers
When a reference cavity made of ultra-low expansion (ULE) glass is temperature-stabilized at the zero-crossing thermal expansion temperature (TCTE=0) with accuracy of 0.1 ◦C, it has a coefficient of thermal expansion (CTE) of less than 2 × 10−10 /K [18]
The analysis shows that passive thermal shielding configurations of reference cavities with a larger thermal time constant will be less sensitive to environmental temperature fluctuations
Summary
Optical reference cavities with finesse of >100,000 are widely used to stabilize the frequency of lasers in optical atomic clocks, precision metrology, high resolution spectroscopy, tests of fundamental physics and deep space navigation [1,2,3,4,5,6,7], which rely on the high frequency stability of lasers. Special geometry and mounting configurations for reference cavities have been developed for less sensitivity to environmental vibration [13,14,15,16,17] When stabilized to those carefully designed reference cavities, lasers with a frequency instability at the 10−16 level at 1-10 s averaging time have been achieved [11, 12, 14, 18, 19], approaching the thermal noise limit of reference cavities [20]. The analysis shows that passive thermal shielding configurations of reference cavities with a larger thermal time constant will be less sensitive to environmental temperature fluctuations. A two-layer thermal shield will help to reduce the temperature fluctuation-induced length instability of a reference cavity below 1 × 10−15 on a day timescale when the cavity has a CTE of 1 × 10−10 /K and is enclosed in a vacuum chamber with temperature fluctuation amplitude of 1 mK and period of 24 hours
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