Laser Safety in LIGO

Abstract

After a journey of some 1.4 billion years, on September 14, 2015, a faint 0.2 s long whisper was detected, first by a gravitational wave detector located in Livingston, Louisiana, and then approximately 7 ms later by a similar detector located at Richland, Washington. The mirrors of the gravitational wave detector moved ever so slightly, enough to stretch the arms of the detector by one ten-thousandth the diameter of a proton. The signal waveform had the shape of a chirp and was consistent with that of the merger of two black holes, one of 35 solar masses with one of 30 solar masses (Fig. 5.1). For the first time, gravitational waves had been directly detected (Abbott et al., 2016). Thus began the era of gravitational wave astronomy. 5.1 Introduction After a journey of some 1.4 billion years, on September 14, 2015, a faint 0.2 s long whisper was detected, first by a gravitational wave detector located in Livingston, Louisiana, and then approximately 7 ms later by a similar detector located at Richland, Washington. The mirrors of the gravitational wave detector moved ever so slightly, enough to stretch the arms of the detector by one ten-thousandth the diameter of a proton. The signal waveform had the shape of a chirp and was consistent with that of the merger of two black holes, one of 35 solar masses with one of 30 solar masses (Fig. 5.1). For the first time, gravitational waves had been directly detected (Abbott et al., 2016). Thus began the era of gravitational wave astronomy. figure FIG. 5.1 The waveforms of the first detected gravitational wave. Original image courtesy of Caltech/MIT/LIGO Laboratory. PPT|High-resolution The two gravitational wave detectors are part of the LIGO Project. LIGO is one of the largest physics projects ever funded by the National Science Foundation. Construction of the LIGO detectors began in 1996. These detectors, known as initial LIGO interferometers (iLIGO), ran from 2002 to 2010 before being shut down to permit the installation of a number of improvements. Construction of the Advanced LIGO (aLIGO) interferometer, a detector ten times more sensitive than an iLIGO interferometer, began in 2011. It included many enhancements, some of which are improved seismic isolation systems, a quieter suspension systems, a greater number of diagnostics signals, and a high-power laser system. Safety plays an important part of any modern workplace. Research is a multidisciplinary field with chemical, electrical, ergonomic, and laser safety all playing a role at LIGO. This article discusses some of the laser safety considerations undertaken by the LIGO Project.

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