Topic : Laser-based method to measure pressure and its derived SI unit ‘pascal’.
Topic in Syllabus: Science & Technology
The US National Institute of Standards and Technology (NIST) scientists have developed a highly precise method for measuring pressurethat is based on treating pressure as energy density — an equivalent physicaldescription to force per unit area because it is derived from the same combination ofthe SI base units.
- The method involves probing atoms of gas in a cavity directly witha laser to determine their pressure.NIST’s new pressure sensor, called a fixed-length optical cavity (FLOC), comparesthe speed of a laser travelling through a gas-filled cavity with that of an identicalbeam in a vacuum.
- The speed of light varies with the density of the gas in a way thatquantum chemists can calculate based on the properties of atoms.
- For a steady-temperature system, metrologists can combine these densitymeasurements — effectively the number of particles in the cavity — with theBoltzmann constant, which relates temperature to kinetic energy.
- This calculates the gas’s ‘energy density’, which is equivalent to pressure
- In short, the method involves probing atoms of gas in a cavity directly with a laser to determine their pressure.
Doing Away with Mercury: The achievement is fantastic from a metrology point of view and if widely accepted by the metrology community, the method would do away with the need for mercury, which is toxic and faces international bans.
Direct Method: Also, the technique measures pressure directly, using a fundamental constant of nature, meaning metrologists can derive the pascal without relying on previous measurements of other quantities, such as density, which the manometer depends on.
Easy Usage: The method is neat as it measures pressure by counting the number of gas particles in the cavity, using just quantum calculations and a fundamental constant of nature. Moreover, it could also allow anyone to measure pressure from first principles without the tedious work of a chain of calibrations to a primary standard that is currently required.
Metrologists have long been striving to replace manometers. This new way to define pressure and its derived SI unit, the pascal will have a lot of potential. Scientists are expecting that this new technique within a year, begin to replace the mercury-based measurement methods that have been in use since 1643.
Instruments that measure pressure are generally classified as:
c. free of hysteresis
d. None of the above