A Fast-Light Enhanced Ring Laser Vibrometer for Detection of Extremely Small Vibrations

Project: Research project

Project Details


Under many scenarios of relevance, it is important to be able to detect remotely signs of clandestine activities, such as operations of dynamic machinery in hidden and possibly subterranean facilities. In principle, such an operation can be identified by detection of small vibrations at characteristic frequencies. However, these signals are expected to be extremely small if the machinery are located at a distance or are underground. The vibration detectors that are currently available have typical sensitivities of 1 micro-g per root Hertz (where g is the acceleration due to Earth’s gravity), and would not be able to detect these signals from a significant distance. Recent developments have shown that new type of detectors, based on the use of the fast-light effect induced by anomalous dispersion, may be able to enhance the sensitivity to vibration by nearly six orders of magnitude1,2,3,4,5,6,7,8,9,10,11,12. The key technology to be used for making a fast-light enhanced vibrometer is a superluminal laser, invented by Prof. Shahriar, which contains a negatively dispersive gain medium, corresponding to a group velocity of light far exceeding the vacuum speed of light, without violating special relativity. The negative dispersion causes a positive feedback effect, so that the frequency shift as a function of a change in the cavity length due to vibration is highly amplified. Under this proposal, we will develop such a vibrometer, using a Rb superluminal laser. Called the Superluminal Ring Laser Vibrometer (SRLV), also invented by Prof. Shahriar, a typical embodiment of the SRLV will consist of two L-shaped ring lasers in parallel, with a figure-8 configuration so that the net area enclosed by each laser is zero. This zero-area configuration ensures that the laser frequency is not sensitive to rotation. The L-shape makes the detector sensitive to the direction of vibration. One of the mirrors on one of the lasers will be mounted on a metallic diaphragm (or a micro-electro-mechanical structure: MEMS) that responds to vibration. The amplitude of vibration will be measured by detecting the beat frequency between the two lasers, so that the signal-to-noise ratio will be determined by quantum noise only under ideal conditions. Preliminary studies of such a vibrometer has shown that it can be constructed in a miniature form, so that three such vibrometers, for detecting vibrations in three orthogonal directions, can fit into a volume as small as 3 cm X 3 cm X 3 cm. Such a device could be deployed in a UAV (unmanned aerial vehicle), an UUV (unmanned underwater vehicle), or a in a clandestine sensor package dropped on the ground from a UAV. Since the sensor is vectorial in nature, two such sensors could be used to pin-point the source of vibration. The SRLV can also be used as an extremely sensitive microphone. As such, this technology can also be useful for audio surveillance and eavesdropping. During Year 1, we will carry out the basic demonstration of an SRLV. During Year 2, we will characterize and optimize the performance of the SRLV, leading to a demonstration of a quantum noise limited vibrometer with a sensitivity of 10 pico-g/√Hz.
Effective start/end date2/1/171/31/22


  • Government of Israel Ministry of Defense Mission to the U.S.A. (PO No. 4441028735 Amnd 2)
  • Department of Defense (PO No. 4441028735 Amnd 2)


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