Infrasound detection by laser diode self-mixing interferometry

Abstract

An alternative technique for infrasound detection based on the self-mixing (SM) interference of a laser diode is described. The principle involved is the dependence of the power emitted by the laser diode on infrasound-induced membrane vibration. The Fourier transform and fringe-counting methods are used to analyze the self-mixing signal. Infrasound signals are experimentally measured from 2 to 20 Hz with a resolution of 0.25, and the results well agree with the theoretical ones.OCIS codes: 120.7280, 230.1040, 280.3420. doi: 10.3788/COL201311.021201.The nominal range of human hearing extends from approximately 20 Hz to 20 kHz. Inaudible sound waves with frequencies below 20 Hz are termed infrasound. These waves can be caused by many natural and anthropogenic sources, such as volcanic eruptions, earthquakes, typhoon, nuclear explosions, spacecraft, and so on [1] . Renewed interest in the detection of infrasound energy in the atmosphere appeared with the creation of the Comprehensive Nuclear-Test-Ban Treaty Organization [2] . A worldwide network of 60 infrasound stations is being established to help monitor compliance with the treaty [3] . Various non-contact, direct-sensing techniques exist, including laser-based interferometric or time-of-flight, capacitive, inductive, optical, and eddy-current (EC) sensing methods [4,5] . Infrasound detection using traditional sensors is based on piezoelectric principles [6] . Bruel and Kjaer market a low-noise microphone (type 4193) that responds at frequencies as low as 0.05 Hz and has impressive noise properties. The optical fiber infrasound sensor (OFIS) is an innovative device comprising two fibers (typically extending from 100 to 1 000 m) connected as a Michelson, Mach-Zehnder, or equivalent interferometer. Considering that the OFIS is longer than the distance over which wind-induced pressure changes are coherent, the effects of wind noise on infrasound detection is reduced, and the signal-to-noise ratio (SNR) is increased over a wide bandwidth [6,7] . These sensors enable accurate measurements but require many optical components, which make these sensors expensive to install and maintain. Eddycurrent (EC) sensors that can perform well in water, are stable with temperature and relatively inexpensive, and have a small form. The EC infrasound sensor reported by Donskoy et al. [4] can detect acoustic signals below 1 Hz at displacement levels of fractions of nanometers. However, when using multiple probes, EC probes interact if mounted sufficiently close to one another.Another alternative technique based on the self-mixing (SM) effect in a laser diode (LD) is presented in this letter.This method has been widely investigated over the last decades particularly for displacement measurements [8−11] . A self-mixing (SM) sensing scheme is advantageous because it does not require an optical interferometer external to the source and an external photo-detector. The laser itself is also used both as a source and a detector, resulting in a very simple and compact setup [12] . In this l...

A Grating Interferometric Acoustic Sensor Based on a Flexible Polymer Diaphragm

“…The LSMI has a high degree of integration. However, due to the complexity of its demodulation algorithm, the LSMI is not suitable for detecting high-frequency acoustic signals and is limited to detecting infrasound [ 16 ]. Compared to other optical interferometric acoustic sensors, GI-based acoustic sensors could be designed with high integration, wide bandwidth, and high acoustic fidelity [ 17 , 18 ].…”