Real time laser power sensor can be integrated into equipment

September 20, 2018 // By Nick Flaherty
A prototype of the smart mirror. Laser light bounces off the highly reflective surface of a silicon plate, visible in the middle of a thick black ring of plastic.  CREDIT Jennifer Lauren Lee/NIST
Researchers from the National Institute of Standards and Technology (NIST) in the US have developed a laser power sensor that could be built into manufacturing devices to provide real-time measurements.

The new device works in a similar way to a previous sensor made by the team, which uses radiation pressure. This shoebox-sized Radiation Pressure Power Meter (RPPM) measures ultrahigh-power lasers of thousands of watts, while the new chip-sized "smart mirror" is designed for lasers of hundreds of watts, the range typically used for manufacturing processes.

"It's still a radiation-pressure power meter, but it's much smaller and much faster," with 250 times the measurement speed of their larger sensor, said NIST's John Lehman. The smart mirror is also about 40 times more sensitive than the RPPM.

The smart mirror sensor can be used for manufacturing in aerospace and automotive as well as cellphones and medical devices. The smart mirror could also be integrated into machines employed in laser-based additive manufacturing 3D printing. The aim is that the sensors could be in every additive manufacturing machine and in every laser weld head.

"This would put the high accuracy of NIST power measurements directly in the hands of operators, providing standardized quality assurance across laser-based systems and helping to accelerate the process of part qualification," which ensures that manufactured objects meet engineering specifications, said NIST's Alexandra B. Artusio-Glimpse.

A 1kW laser beam has a small but noticeable force--about the weight of a grain of sand. By shining a laser beam on a reflective surface, and then measuring how much the surface moves in response to light's pressure, researchers can both measure the laser's force (and therefore its power) and also use the light that bounces off the surface directly for manufacturing work.

The RPPM shines the laser onto a laboratory weighing scale, which depresses as the light hits it, but this is too big to be integrated into welding heads or 3D printers. The "smart mirror" works essentially as a capacitor,  measuring the changes in capacitance between two charged plates..

The top plate is coated with a highly reflective mirror called a distributed Bragg reflector, which uses alternating layers of silicon and silicon

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