Calibration of the LIGO displacement actuators via laser frequency modulation

TL;DR

This paper introduces a laser frequency modulation method for calibrating LIGO's displacement actuators, achieving high precision without force application, and providing a novel, efficient calibration approach.

Contribution

The paper presents a new laser frequency modulation technique for actuator calibration that is force-free and offers high accuracy, differing from traditional methods.

Findings

Achieved less than 1% uncertainty in calibration

Demonstrated effective length variation calibration via laser frequency modulation

Provided a single-step, force-free calibration method

Abstract

We present a frequency modulation technique for calibration of the displacement actuators of the LIGO 4-km-long interferometric gravitational-wave detectors. With the interferometer locked in a single-arm configuration, we modulate the frequency of the laser light, creating an effective length variation that we calibrate by measuring the amplitude of the frequency modulation. By simultaneously driving the voice coil actuators that control the length of the arm cavity, we calibrate the voice coil actuation coefficient with an estimated 1-sigma uncertainty of less than one percent. This technique enables a force-free, single-step actuator calibration using a displacement fiducial that is fundamentally different from those employed in other calibration methods.