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  • Laser Sensor Means Rifle Hits Bull's-Eye Every Time
Apr 2011
OAK RIDGE, Tenn., April 26, 2011 — Military and police marksmen could see their rifle sights improve with a fiber optic laser-based sensor system that automatically corrects for even tiny barrel disruptions.

The system, developed by a team led by Oak Ridge National Laboratory's (ORNL) Slobodan Rajic, precisely measures the deflection of the barrel relative to the sight and then electronically makes the necessary corrections.

A laboratory prototype of Oak Ridge National Laboratory’s Reticle Compensating Rifle Barrel Reference Sensor allows Slobodan Rajic to fine-tune the technology. The system precisely measures the deflection of the barrel relative to the sight and then electronically makes corrections. (Image: Ron Walli)

The Reticle Compensating Rifle Barrel Reference Sensor shifts the burden of knowing the relative position between the barrel and the weapon sight axes from the shooter to an electronic sensor. The system precisely measures the deflection of the barrel relative to the sight and then electronically realigns the moving reticle, or crosshairs, with the true position of the barrel, or bore axis.

"When a weapon is sighted in, the aim point and bullet point of impact coincide," Rajic said. "However, in the field, anything that comes into contact with the barrel can cause perturbation of the barrel and induce errors."

With modern high-caliber rifles boasting ranges of up to two miles, even very small barrel disruptions can cause a shooter to miss by a wide margin.

The typical barrel of a high-power rifle has exterior grooves, called flutes, to reduce weight and create more surface area to enable the barrel to cool faster. The barrel heats up as a result of the hot expanding gases in the barrel and from the friction of the bullets, which are propelled by these hot gases along a helical path inside the barrel.

With the technology, glass optical fibers are placed into the flutes. These flutes are either produced by the barrel manufacturer or are retrofitted. The sensor system contains a laser diode that sends a signal beam into the optical fibers parallel to the bore axis of the barrel.

"The optical fibers are designed to split the laser beam twice, sending one beam along the top of the rifle barrel and another light beam along the side of the barrel," Rajic said. "Thus, we can measure both the vertical and horizontal barrel deflection."

Through a combination of algorithms, optics and additional sensor inputs, the system can take into account distance and other factors affecting the bullet’s trajectory. Ultimately, the shooter is left with crosshairs that automatically adjust for conditions in real time.

The resolution of the Reticle Compensating Rifle Barrel Reference Sensor is 250 times better than that of traditional reticles, which can normally be manually adjusted by one-fourth minutes of angle. The ORNL sensor can detect angular displacement and shift the reticle by 1/1000th of a minute of angle, Rajic said.

Rajic and his colleagues are also developing a laser-based bullet-tracking system that increases the shooter’s odds of hitting the target by providing specific information about the bullet flight path.

UT-Battelle manages ORNL for the Department of Energy's Office of Science. Other developers of the technology are Panos Datskos, Troy Marla and Bill Lawrence. Funding for the project has been provided by the US Army, Picatinny Arsenal, Joint Services Small Arms Program.

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fiber optic sensor
Any device in which variations in the transmitted power or the rate of transmission of light in optical fiber are the means of measurement or control. Fibers can be used to measure temperature, pressure, strain, voltage, current, liquid level, rotation and particle velocity.
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