Adaptive Optics for Aberration Control in Einstein Telescope
Abstract
:1. Introduction
2. Core Optics for Third-Generation GW Detectors
2.1. Current Mirror Technologies
2.2. Challenges and Requirements for ET
3. Wavefront Distortions and Thermal Effects
3.1. Wavefront Distortions and Their Impact on the Interferometer Performance
3.2. Sources of WD and Thermal Effects
4. Design and Operation of a Thermal Compensation System
4.1. Requirements
- Actuation range. The actuators must handle the largest expected WD——with additional capacity to accommodate variations over time—at least by a factor of two.
- Actuation precision. Actuators must achieve sufficient resolution to prevent introducing new distortions that exceed allowable SNR losses
- Sensor range and precision. The sensor must be able to detect—while the detector still operates—the maximum expected residual distortion. Regarding its precision, it is usually required to be good enough such that random error in any measurement is less than one order of magnitude of the root mean square (RMS) tolerable WD .
- Bandwidth. The actuator must be able to properly compensate for any thermal change to keep within the maximum acceptable value. The bandwidth is computed from the thermal time constant of the effect to be compensated for. For static WDs, a DC-only control is usually required.
- Noise. Both sensors and actuators can inject noise at all frequencies—including in the sensing bandwidth of the detector, in which it could even limit and dominate the sensitivity in a specific frequency range. Therefore, the injected noise of the actuators and their couplings with the interferometer must be properly computed and considered in the design phase.
4.2. Sensors
4.2.1. Direct Sensing: Hartmann Wavefront Sensor
4.2.2. Indirect Sensing: Phase Camera
4.3. Actuators
4.3.1. Ring Heaters
4.3.2. CO2 Lasers Projector
5. Future Prospects for Thermal Effects Mitigation
6. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Abbreviations
CCD | Charge-Coupled Device |
CH | Central Heating |
CO | Core Optics |
CP | Compensation Plate |
CTN | Coating Thermal Noise |
DAS | Double Axicon System |
DM | Deformable Mirror |
ET | Einstein Telescope |
ET-HF | Einstein Telescope High-Frequency |
ET-LF | Einstein Telescope Low-Frequency |
ETM | End Test Mass |
GW | Gravitational Wave |
HOM | Higher Order Mode |
HP | Hartmann Plate |
HWS | Hartmann Wavefront Sensor |
ITM | Input Test Mass |
KAGRA | Kamioka Gravitational Wave Detector |
LMA | Laboratoire des Matériaux Avancés |
PC | Phase Camera |
RH | Ring Heater |
RMS | Root Mean Square |
RoC | Radius of Curvature |
SLED | Superluminescent Light Emitting Diode |
SNR | Signal-to-Noise Ratio |
TCS | Thermal Compensation System |
TM | Test Mass |
WD | Wavefront Distortion |
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Flatness | Thickness Uniformity | Absorption | Scattering |
---|---|---|---|
<0.5 nm RMS | 0.05% | <0.4 ppm | <10 ppm |
(within ⊘ 150 mm) | (within ⊘ 150 mm) |
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Cifaldi, M.; Taranto, C.; Aiello, L.; Lumaca, D. Adaptive Optics for Aberration Control in Einstein Telescope. Galaxies 2025, 13, 18. https://doi.org/10.3390/galaxies13020018
Cifaldi M, Taranto C, Aiello L, Lumaca D. Adaptive Optics for Aberration Control in Einstein Telescope. Galaxies. 2025; 13(2):18. https://doi.org/10.3390/galaxies13020018
Chicago/Turabian StyleCifaldi, Maria, Claudia Taranto, Lorenzo Aiello, and Diana Lumaca. 2025. "Adaptive Optics for Aberration Control in Einstein Telescope" Galaxies 13, no. 2: 18. https://doi.org/10.3390/galaxies13020018
APA StyleCifaldi, M., Taranto, C., Aiello, L., & Lumaca, D. (2025). Adaptive Optics for Aberration Control in Einstein Telescope. Galaxies, 13(2), 18. https://doi.org/10.3390/galaxies13020018