The world of mass, force, and laser power calibration is currently in flux. The international basis for mass measurement is shifting from a cylinder of metal stored outside of Paris to a system defined by the fundamental structure of the universe. In the new system of measurement, mass measurements will arise from a number, called Planck’s constant, that relates a system’s energy to its frequency.
A benefit of this redefinition is that mass and force measurements can be scaled up or down as necessary using physical processes other than the gravitational force acting on a physical mass. One of the possibilities for new physical processes to use in the calibration of mass and force is photon pressure – the force that light imposes on material when it reflects off a surface.
NIST-on-a-Chip researchers are using photon pressure and other techniques to create devices that will measure masses and forces in new ways. The prototypes are compact, highly sensitive, and self-calibrating, and could be embedded into existing manufactured goods.
Acceleration measurement is a several-billion-dollar-a-year industry. Many products require measurement of acceleration or changes in motion – car airbags, aircraft navigation, cell phones. But current devices that are used have to be regularly calibrated.
The NIST-on-a-Chip researchers’ goal is to make the most accurate accelerometry instrument in the world smaller than a pencil eraser and cost-effective for manufacturing, which will ease commercialization. Creating a calibration instrument as good as any in the world that stays in users’ labs would allow companies to maintain their systems without unnecessary downtime, and develop new products with shorter time to market. And because of the small size of the accelerometers, they could be embedded into manufactured devices as a built-in reference.
Also, more accurate and sensitive accelerometers may allow entirely new applications. The devices may permit blind navigation for longer periods of time during GPS jamming, or more precise measurement of subsurface geologic structures in energy exploration. The potential scope of application areas is vast, ranging from national security to medical applications such as intra-cranial ultrasound imaging.
The force produced by photon pressure can be calculated from the amount of reflected optical power and the speed of light. The NIST-on-a-Chip project exploits this link to provide compact calibration systems that allow the measurement of mass or force from laser power, or vice versa. The use of photon pressure forces provides a synergy: In the low force domain, using laser power calibrations reduces force uncertainties. In the large laser power domain, using calibrated masses reduces laser power uncertainties.
Applications for the prototype force/mass sensors being built at NIST include improving calibration of atomic force microscopes; making a sensitive but disposable balance for measuring amounts of hazardous wastes in the field; and improving laser power measurements.