A 4 km fibre line turned thunder shakes into an image of the shallow crust. Aluminium foil cut by laser in as little as 15 seconds offers a low-cost alternative to expensive terahertz polarisers.
A Penn State team turned 458 thunderquakes recorded over two years by a 4 km fibre-optic line beneath its campus into an image of the ground below. The cable read the ground vibration from thunder rather than the sound travelling through the air. Small ground movements left by a common weather event became a usable signal for examining the structure of the shallow crust.[1]
The cable's sensitivity was not the only striking part of the method. The model used by the researchers had been expected to be too crude for this task, yet the two-year record was enough to distinguish shallow structure around the line. The result shows that thunderquakes in long-running fibre records can be readable geoscience data rather than vibrations to be discarded as noise.[1]
A TMOS team at the Australian National University also turned ordinary aluminium kitchen foil into a wire-grid polariser with nanosecond laser pulses. Cutting took as little as 15 seconds. Commercial polarisers that filter terahertz light along a selected direction sell for thousands of dollars, while this approach starts with a much easier material to obtain. The report says the foil could replace costly commercial units; it does not say that it has already displaced them in every application.[2]
