Scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) have developed technology that is in fact throwing light on certain smallest particles to detect their presence — and it is developed from tiny glass bubbles.
The technology is based on a unique physical phenomenon called the “whispering gallery,” described by physicist Lord Rayleigh (John William Strutt) in 1878 and named after an acoustic effect inside the dome of St Paul’s Cathedral in London. It was possible to clearly hear the whispers made at one side of the circular gallery at the opposite side. This is due to the travel of sound waves along the walls of the dome to the other side. This effect can be reproduced by light in a tiny glass sphere with a width just equal to the breadth a strand of hair, known as a Whispering Gallery Resonator (WGR).
Upon shining light into the sphere, it bounces around the inner surface again and again, forming an optical carousel. Photons that bounce along the inner surface of the tiny sphere can end up traveling for long distances, as long as 100 m at times. However, every time a photon gets bounced off the surface of the sphere, a small amount of light escapes. This leaking light forms a kind of aura around the sphere, called as an evanescent light field.
When nanoparticles enter the range of this field, its wavelength is distorted by them, thus effectively altering its color. Researchers can monitor these changes in color and use the WGRs as a sensor; earlier, different research teams used them to detect individual virus particles in solution, for instance. However, researchers at OIST’s Light-Matter Interactions Unit observed that enhancements to prior work can be made to develop even more sensitive designs. The research has been reported in the journal Optica.