This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: An international team of physicists has developed a new method for determining the precise color of laser light using an image that rotates as the laser's frequency shifts. The finding could offer a new way to ensure that lasers are 'locked' to the frequencies needed by technologies that rely on them, from GPS positioning to quantum sensors.
It could also spur developments in spectroscopy, magnetometry and quantum communications. In a new paper published in the journal Optica, the University of Glasgow-led team describes how it devised a way to determine the frequency of a laser beam in a single snapshot. The team's method starts by passing two differently configured beams of laser light through a gas of rubidium atoms held in a glass cell.
One beam comes from a traditional laser with a single polarization: Its electric field oscillates in a uniform direction. The other uses structured light known as a vector beam, with a ring-shaped intensity profile. Its polarization changes at each point around the ring.
As the first beam travels through the rubidium atoms, its electric field aligns them, shepherding around 90% into a single quantum state. This alignment affects how the atoms respond to the polarization of the structured light from the second beam as it travels through the gas from the opposite direction. The interaction between the light and the rubidium atoms becomes stronger or weaker as the laser's frequency shifts closer to or further from the atoms' natural resonance, changing the light's polarization structure.
The team visualizes this effect by separating the emerging light into different polarization components and capturing the resulting images with a digital camera. The telltale signs of how the atoms have affected the structured laser beam appear in the image as a pattern of bright 'lobes' of light around the laser's ringed shape. As the frequency changes, the lobes rotate around the ring.
As the absorption of polarized light changes, they become brighter or darker. Together, these features give the team a visual indicator in a single image of how closely the laser's frequency matches the atoms' resonance or how far it has drifted. Professor Sonja Franke-Arnold of the University of Glasgow's School of Physics & Astronomy led the research.
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