Source: Laser Focus World.

To save infrastructure costs, different types of refined oil are often transported over a single pipe at alternate times. Consequently, sensors that can easily, quickly, and safely determine the proportions of components in a refined-oil mixture are invaluable for tracking, routing, and ultimately rerefining the mixtures. Scientists at Tianjin University (Tianjin, China) are now experimenting with terahertz time-domain spectroscopy at frequencies between 0.25 and 1.5 THz to determine the proportions in a mixture of gasoline and diesel.

In the time-domain spectroscopy (TDS) system, 50 fs pulses at an 800 nm wavelength from a Ti:sapphire laser are split into pump and detection pulses, with the pump pulse used to stimulate terahertz radiation from a photoconductive antenna and the detection pulse acting on a photoconductive-antenna detector in concert with the terahertz signal. Information from reference and sample pulses are Fourier-transformed to provide the refractive index and absorption coefficient of the oil mixtures.

Mixtures of 97# gasoline and -10 diesel with a sample thickness of 10 mm were measured. Results for the gasoline component were very accurate, but the results were a mean of 4.3% off for the diesel¡ªthe latter to be corrected by adopting a modified form of the Beer-Lambert absorption-coefficient law. Contact Yi-nan Li at lin860405@gmail.com.