The LIGO Laboratory congratulates Dr. Ling “Lilli” Sun of Caltech for winning this year’s LIGO Laboratory Award for Excellence in Detector Characterization and Calibration. Her outstanding contributions to estimation of gravitational-wave strain incident upon the LIGO detectors in near real time, including systematic error and uncertainty, are foundational to all results generated with Advanced LIGO data collected during the current observing run (O3).
The LIGO detectors are Michelson laser interferometers with kilometer-scale resonant cavities for arms, whose primary output is captured by infrared photodiodes. The effect of a gravitational wave appears on the photodiode signal via a complex transfer function, along with a variety of noise sources. The process of modeling the detectors, and subsequently reconstructing of this estimated strain signal and noise (differential arm cavity length change per arm length) from the digitized photodiode signals with those detector models, is referred to as calibration. These models are informed by a large collection of measurements, and have uncertainties and systematic errors that must be quantified. A successful model of each interferometer’s response must be frequency-dependent in both magnitude and phase and slowly time-varying, to track the reality of the detector with the accuracy and precision necessary for rigorous astrophysical parameter estimation [1-5]. The calibration model, its uncertainties, and systematic error estimates must also change as the detectors’ hardware and control systems are changed between and during observation runs.
Dr. Sun played a leading role in every part of constructing the detector models and uncertainties for both LIGO detectors leading up to and during the third observing run (O3). She refined the software used to create the interferometer and used that refined software on both detectors to:
- provide new, quantitative analysis of systematic errors traditionally thought as negligible,
- collate all measurements for estimating the overall uncertainty and systematic error in the model,
- develop an analysis pipeline to produce said uncertainty and systematic error estimate every hour in real time,
- handle new features in the detectors that had not been found previously,
- document all of that work in an organized, approachable way such that it’s traceable, reproducible, and accessible to the LIGO calibration team.
Dr. Sun’s work has enabled a wide range of gravitational-wave analyses, including minutes-latency public event candidate alerts and tests of general relativity. All of her essential contributions through this work proved to be even more valuable with a significantly higher event detection rate in O3 than O2.
Dr. Sun will receive a $1,000 prize and will present an invited colloquium at one of the LIGO Laboratory sites (LIGO-Hanford, LIGO-Livingston, Caltech, or MIT) to share her achievements with LIGO Laboratory members. She will receive an award certificate at the LIGO-Virgo Collaboration meeting in March 2020.
Read more about her work:
 Abbott, Benjamin P., et al. "Calibration of the Advanced LIGO detectors for the discovery of the binary black-hole merger GW150914." Physical Review D 95.6 (2017): 062003.
 Karki, S., et al. "The Advanced LIGO photon calibrators." Review of Scientific Instruments 87.11 (2016): 114503.
 Tuyenbayev, D., et al. "Improving LIGO calibration accuracy by tracking and compensating for slow temporal variations." Classical and Quantum Gravity 34.1 (2016): 015002.
 Cahillane, Craig, et al. "Calibration uncertainty for Advanced LIGO’s first and second observing runs." Physical Review D 96.10 (2017): 102001.
 Viets, A. D., et al. "Reconstructing the calibrated strain signal in the Advanced LIGO detectors." Classical and Quantum Gravity 35.9 (2018): 095015.
2019 Honorable Mention
The LIGO Laboratory is also pleased to list three other projects as meriting honorable mention:
Pep Covas (University of the Balearic Islands) -- for improving searches for continuous wave gravitational wave sources by identifying narrow spectral artifacts in the detector output, identifying and characterizing their sources, and mitigating their impact on the astrophysical reach of searches for continuous waves.
Chiara Di Fronzo (University of Birmingham) -- for studies aimed at reducing relative motion of the internal seismic isolation platforms, particularly at low frequencies where wind and earthquakes mainly affect interferometer sensitivity and stability.
Patrick Meyers (The University of Melbourne) -- for his leadership in the development and implementation of a variety of data quality cuts that significantly improved the performance of searches for a stochastic gravitational wave background performed in O1 and O2, as well as his characterization of environmental noise sources expected to affect current and future detectors.