Whispering gallery mode (WGM) res- onators have been suggested for use as reference cavities for laser stabilization. Because of their unique properties (small size, high stability, narrow line width), such application appears to hold great promise. It is expected to allow for the exceptionally high optical frequency stability.
The main practical difficulty associated with using WGM resonators for laser stabilization arises from the fundamental fact that the light propagates inside an optical material. This appears to be a disadvantage compared with low-expansion Fabry-Perot resonators that are essentially vacuum-filled. In WGM resonators, the material’s optical properties set the limit not only for the resonator’s Q-factor, but also for its stability.
The most important factors contributing to variation of the WGM resonance frequency are the thermal refractivity and thermal expansion. These variations can be suppressed if the resonator temperature is stabilized to the micro-Kelvin level. To achieve this, the temperature dependence of the resonator’s own anisotropy is used.
Temperature dependence of the resonator anisotropy leads to a temperature-dependent frequency difference between the TE and TM mode families. This frequency difference can be measured with a high precision, and the temperature variations are extracted. These variations are then suppressed by two digital control loops.
The first practical implementation of the dual-mode stabilization approach has been achieved, and active temperature stabilization of a WGM resonator at above room temperature has been demonstrated. Temperature stabilization at the level of 200 nK was achieved when integrated for one second, and below 10 nK when integrated for 10,000 seconds. This considerably surpasses state-of-the-art temperature sensors; especially temperature control techniques. This result is significant not only in the context of laser stabilization, but also as a demonstration of a novel temperature sensor with a broad spectrum of potential applications.
A WGM-based temperature sensor with nano-Kelvin sensitivity operating at room temperature was demonstrated. It was used to stabilize a WGM resonator at the level of a few nano-Kelvin, which will allow use as an ultra-stable laser lock reference. The demonstrated technique can be used in a variety of other applications requiring high temperature stability, as well as ultra-sensitive measurements of temperature variations. These include thermal stabilization of a quartz oscillator, mid- or far-IR sensitive bolometers, precise calorimetric measurements in chemistry, and study of optical and mechanical aging effects in various crystalline resonators.
This work was done by Dmitry V. Strekalov, Nan Yu, Robert J. Thompson, and Ivan S. Grudinin of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48222
This Brief includes a Technical Support Package (TSP).
Temperature Measurement and Stabilization in a Birefringent Whispering Gallery Resonator
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Overview
The document titled "Temperature Measurement and Stabilization in a Birefringent Whispering Gallery Resonator" is a technical support package from NASA's Jet Propulsion Laboratory (JPL) that discusses advancements in temperature measurement and stabilization techniques using whispering gallery mode (WGM) resonators. These resonators are optical devices that can enhance precision in various applications, including optical clocks and sensors.
The document outlines the significance of WGM resonators in achieving high sensitivity and stability in temperature measurements. It emphasizes the use of birefringent materials, which can improve the performance of these resonators by allowing for better control over light propagation and resonance characteristics. The ability to stabilize temperature is crucial for maintaining the accuracy and reliability of optical systems, particularly in environments where temperature fluctuations can affect performance.
Key contributors to the research include members of the Quantum Sciences and Technology group at JPL, such as Dmitry V. Strekalov, Lukas Baumgartel, Rob Tompson, Ivan Grudinin, and Nan Yu. Their work focuses on integrating miniature physics packages that utilize WGM resonators to create ultra-compact optical clocks. These clocks aim to provide significant improvements over traditional microwave clocks in terms of size, weight, and power consumption, targeting a device that is less than 10 kg and consumes less than 20 watts.
The document also discusses the potential applications of these technologies beyond aerospace, highlighting their relevance in commercial and scientific fields. The advancements in WGM resonators could lead to more efficient and precise measurement systems, which are essential for various technological developments.
In summary, this technical support package presents a comprehensive overview of the research and innovations in temperature measurement and stabilization using birefringent WGM resonators. It underscores the collaborative efforts at JPL to push the boundaries of optical technology, aiming for compact, high-performance devices that can revolutionize timekeeping and measurement systems across multiple domains. The document serves as a resource for understanding the implications of this research and its potential impact on future technological advancements.
