Radiation Shield Geometry for Low-BBR Optical Lattice Clocks
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Solution Overview
Problem
Current radiation shields for optical lattice clocks face challenges in reducing blackbody radiation shifts, particularly due to room temperature radiation leakage through apertures, which affects the accuracy of clock transition frequency measurements, and existing low reflection coatings do not effectively manage diffuse reflection characteristics.
Innovation Solution
A radiation shield design that considers the geometrical shape of the inner wall surface to minimize the difference in blackbody radiation shifts between mirror and diffuse reflection conditions, using a ray tracing method to calculate and optimize the reflectance values, allowing for a reduction in uncertainty to 10−19 or less, even when the exact reflection characteristics are unknown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a radiation shield with apertures is used to allow atoms and laser beams to pass through, then the optical lattice clock can operate, but room temperature radiation leaks into the shield through the apertures causing blackbody radiation shifts
Solution Approach 1:
A cryogenic radiation shield is introduced as an intermediary component between the room temperature environment and the atoms. The shield is cooled to cryogenic temperatures (e.g., 4K) to reduce thermal radiation, while apertures allow laser beams and atoms to pass through. This mediator blocks harmful room temperature blackbody radiation while permitting necessary optical and atomic processes to occur.
Solution Approach 2:
The temperature parameter of the radiation shield is changed from room temperature to cryogenic temperatures. By cooling the shield walls to very low temperatures, the thermal radiation emitted by the shield surfaces is dramatically reduced (following Stefan-Boltzmann law where radiation power is proportional to T^4), thereby minimizing blackbody radiation shifts affecting the atoms.
2Object-affected harmful factors
If the size of apertures is reduced to minimize radiation leakage, then less room temperature radiation enters the shield, but the clock transition measurement becomes more difficult
Solution Approach 1:
The temperature parameter of the shield is changed to cryogenic levels, which compensates for the small aperture size. The extremely low temperature reduces thermal radiation so significantly that even small apertures provide sufficient blocking, while still allowing adequate laser beam transmission and atom passage for clock operation.
3Object-affected harmful factors
If an absorbing material is disposed on the inner wall surface to reduce blackbody radiation influence, then some radiation is absorbed, but low reflection coating still has reflectance causing multiple reflection and diffusibility
Solution Approach 1:
The temperature parameter of the shield is reduced to cryogenic levels, which dramatically reduces the intensity of thermal radiation emitted by the inner wall surfaces. This reduces the overall blackbody radiation field that atoms are exposed to, making the absolute level of reflection less critical.
Solution Approach 2:
Instead of requiring perfect absorption (100% absorption coefficient), a low reflection coating with moderate reflectance (e.g., 10-20%) is applied. The cryogenic temperature provides sufficient radiation suppression even with this partial absorption, simplifying the coating requirements while maintaining measurement accuracy.
4Object-affected harmful factors
If the radiation shield is cooled to cryogenic temperature, then blackbody radiation energy is reduced, but the device complexity increases
Solution Approach 1:
The temperature parameter is changed to cryogenic levels to achieve the desired radiation suppression. This parameter change is necessary to reach the 10^-19 uncertainty level, and the complexity of the cooling system is accepted as a trade-off for achieving this extreme precision in clock frequency measurement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optimized radiation shield design significantly reduces the uncertainty in clock transition frequency measurements by minimizing the influence of blackbody radiation shifts, achieving higher accuracy for Sr atoms and potentially other atomic species, such as Yb, Mg, Cd, and Hg, by designing the shield to have a geometrical shape that maintains a low frequency difference between diffuse and mirror reflection scenarios.
Implementation Method 1
blackbody radiation (BBR), that is, the Stark shift arising from blackbody radiation (BBR shift) having its origin in a radiation field governed by Stefan-Boltzmann Law
Implementation Method 2
a condition where the inner wall surface exhibits mirror reflection
Implementation Method 3
a condition where the inner wall surface exhibits diffuse reflection
Data Source
AI summary
Provided according to an embodiment of the present disclosure is a radiation shield 10 including a shield wall surrounding a hollow region capable of accommodating therein atoms for an optical lattice clock 100, the shield wall having, provided therein, at least two apertures communicating with outside. A geometrical shape of an inner wall surface of the shield wall is configured such that a difference between BBR shifts found under two conditions does not exceed a predetermined value over a range of position of atoms, the BBR shifts being caused in atoms 2 by emitted radiation emitted by the inner wall surface, incoming radiation leaking in from the outside through the apertures, and a reflection component of the emitted radiation and incoming radiation at the inner wall surface, the two conditions being a condition where the inner wall surface exhibits mirror reflection and a condition where the inner wall surface exhibits diffuse reflection, the range being where clock transition operation is carried out in the optical lattice clock, the inner wall surface facing the hollow region. Provided according to other embodiments of the present disclosure also are the optical lattice clock 100 including such a radiation shield, and a design method for the radiation shield.