Assertion Supported AI assessment confidence: 95% certainty 5/5 debate potential 1/5

Adhikari: Laser radiation pressure physically moves LIGO's 40-kilogram mirrors

Rana Adhikari · The Technical Challenges of Measuring Gravitational Waves - Rana Adhikari of LIGO · Y Combinator · Sep 15, 2017 · at 21:53

Caltech physics professor and LIGO scientist Rana Adhikari explains the technical challenges of managing laser-induced radiation pressure in gravitational wave detectors.

0:00 / 0:18exact quote · 18.4s

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“There's so much laser power that when you, it's weird to think about, but there's so much laser power when we hit the mirror, it moves the mirror. And the mirror, if you, to imagine it, is about this big. And it is 40 kilograms”

quote is from the automated transcript, cleaned for reading: filler sounds and stutters are removed, nothing is rephrased. names can be misheard (the analysis reads context, assessments check outside sources). how →

The claim, plainly

The laser power inside LIGO exerts enough radiation pressure to physically move its 40-kilogram suspended mirrors.

a quote alone can be ambiguous, so this restates it with the references and context of the conversation around it resolved. AI-written; the tape below the player is the source.

Assessment

Scientific literature and Advanced LIGO technical documentation confirm both parts of the claim. Advanced LIGO's primary suspended test mass mirrors are fused silica cylinders weighing approximately 40 kg each. At high circulating cavity power (hundreds of kilowatts), the radiation pressure of the laser beam exerts forces on the order of millinewtons, inducing measurable physical displacement, optical spring effects, quantum radiation pressure noise, and dynamic angular instabilities (the Sidles-Sigg effect). Furthermore, LIGO routinely uses dedicated auxiliary lasers (Photon Calibrators) that intentionally displace the 40 kg mirrors via radiation pressure for interferometer calibration.

Advanced LIGO primary test masses are cylindrical fused silica mirrors weighing approximately 40 kg each, suspended as the bottom stage of a quadruple pendulum system.
Circulating laser power of several hundred kilowatts in the Fabry-Pérot cavities exerts steady and fluctuating forces on the order of millinewtons, causing physical displacement and optomechanical spring effects on the test masses.
Published studies (e.g., Sidles & Sigg 2006; Hirose et al. 2010; Dooley et al. 2013) demonstrate that radiation pressure creates optical torques that rival or exceed mechanical restoring torques, inducing angular instabilities.
LIGO's Photon Calibrators actively employ radiation pressure from auxiliary lasers to displace the 40 kg end test masses by calibrated amounts between 10^-18 m and 10^-15 m (Karki et al., 2016).

Checked against

[1] ligo-india.in [2] quarknet.org [3] eoportal.org [4] caltech.edu [5] optica.org [6] lsu.edu [7] mdpi.com [8] uliege.be

"Sidles-Sigg" "Advanced LIGO" "torque" "radiation pressure" "40 kg" Advanced LIGO test mass weight radiation pressure physical displacement mirror Advanced LIGO test mass 40 kg radiation pressure optical spring Sidles Sigg instability "radiation pressure" "40 kg" LIGO "optical spring" OR "displacement" "photon calibrator" LIGO "radiation pressure" "40 kg" mirror displacement

assessed as of 2026-09-05

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Mentioned

Caltech LIGO

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Adhikari: Laser radiation pressure physically moves LIGO's 40-kilogram mirrors

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