Radiation pressure is a force that results when light reflects from a mirror. By measuring the force on a mirror, the power in a laser beam can be assessed. We have invented a miniaturized mirrored force sensor that combines several key elements to make a sensor that is smaller, faster, more sensitive to force and less sensitive to noise, gravity, and thermal effects.
This invention measures the power of a laser beam by detecting the displacement caused by photon pressure on a mirrored surface. Accurate measurement and control of laser power measurement is essential to manufacturing. However, to date there has been no way to precisely measure laser power during a manufacturing process. Without this information, some manufacturers may have to spend more time and money assessing whether their parts meet manufacturing specifications after production.
NIST’s photon momentum sensor, or smart mirror, by contrast, is designed to create a compact laser power sensor that could be included in the laser head and potentially be used in fast inline process monitoring. Mounted beneath the top reflecting plate is a second plate. The two plates form a capacitor, the capacitance of which depends on how much the top place is displaced by photon pressure.
It is a radiation-pressure power meter (RPPM) that employs a dual spring detector concept. Two identical springs are used in a tandem configuration that mitigates environmental vibration signals, as well as errors due to changes in the sensor tilt. This method improves both sensitivity and speed (250 times faster than RPPM) and makes it a strong candidate for use in applications requiring a small compact sensor.
The smart mirror provides new opportunities for manufacturers of lasers used in additive manufacturing (interchangeably known as 3D printing) and welding, which require low-beam intensity in the midrange. This approach allows the sensor to be embedded at the end of a robotic arm or in additive manufacturing and laser welding systems where the laser head will move and rotate. The size and reliability of this device enables it to be incorporated within the laser itself and measure performance while the laser is being used. This will help accelerate the parts qualification process.