School of Chemistry & Physics

Scientific Reports Publication Focuses on Accurate Measurements of Speed of Light

Research by Professor Naven Chetty in the School of Chemistry and Physics (SCP) and Mr Oelof Kruger of the National Metrology Institute of South Africa (NMISA) involving the use of a vacuum air refractometer for accurate and convenient measurement of the refractive index of air was featured in the Scientific Reports publication of the prestigious Nature journal.

‘Having an article published in this journal is considered laudable in the scientific community considering the high rejection rate within the Nature group of journals,’ said Chetty. ‘Being featured in such a multidisciplinary publication demonstrates that our work is multidimensional and straddling the fields of engineering and physics.’

Chetty’s expertise lies in applied physics, with much of his research focusing on biomedical physics, while Kruger is head of the Length Section at NMISA, dedicated to the maintenance, research and dissemination of realisation of the SI definition of the metre in South Africa.

Titled: Development of a Permanent Vacuum Hollow Prism Air Refractometer for use in Dimensional Metrology, their paper covers research that makes important contributions to the science of measurement by testing the accuracy of a modified, portable air refractometer – an instrument used to measure the speed of light in air – that is more convenient to use for everyday applications and more stable over long-term usage than traditional air refractometers, and which may provide more accurate measurements.

Since the international system of units (SI) defines the unit of a metre as the speed of light in a vacuum, accurately determining the speed of light in air is essential to ensure a reliable standard measurement for countless applications, and has to take into consideration several environmental factors when conducted in the air.

Refractive index measurements compensate for changes in the speed of light due to these conditions, and are used in applications from optometry to veterinary medicine to urology, and even the food industry. Air refractometers provide this index measurement.

These instruments commonly use a tube design as the etalon device that measures the small changes in the wavelength of light, but Chetty and Kruger’s research employed a commercial prism to function as the vacuum etalon. They focused on the design, fabrication and testing of this modified refractometer that uses a permanent vacuum and an added laser path for improved stability, and which does not require a vacuum pump, making it easier to use but equally as accurate as other refractometers.

This novel research, building on prior research by Kruger and Chetty and using their low-cost air refractometer design, achieved results with high accuracy that will be important for everyday use as well as for improved accuracy in research.

Words: Christine Cuénod

Photographs: Supplied