Imagine a laser-like beam of light — the one found in barcode scanners and laser printers, brilliant and extraordinarily precise. Its light particles move step by step with each other, producing what physicists call coherent light: a beam that can cut steel, transmit information and stimulate the generation of new skin cells. Traditionally, producing coherent light involves using other lasers, which is expensive and energy-demanding; however, Trinity researchers suggest we can create high-tech lasers using any kind of light — including sunlight!
To grasp the idea behind their theory, let’s delve into the physics of light first. The light itself is made of tiny particles called photons. Usually, photons resemble billiard balls that continuously bump into each other and ricochet in random directions. Each particle has a unique movement trajectory, so we can think of them as individuals spreading out freely across space. However, to make a bright and precise beam of laser light, the photons’ movement must become more coordinated. This means photons would need to lose their ‘individuality’, becoming one collective power in which every particle moves synchronously and in one direction relative to the other ones.
Here is the moment when things get interesting. Photons belong to a class called bosons, which, by their quantum nature, prefer to occupy the same state as particles around them. Under normal conditions, warmer temperatures disrupt this tendency because it leads to more chaotic movement; however, when photons are cooled enough, they lose energy and settle into a lower energy state. When this happens, photons have less opportunity to be disorganised, which allows them to start acting as a whole, united collective, merging into a synchronous march of light particles. Eventually, they become a super-photon — the most organised form of light ever encountered.
This phenomenon is known as Bose-Einstein condensation, and it lies at the very core of the theory proposed by Luísa Toledo Tude, Emily Haughton and Paul Eastham. Put simply, their theoretical analysis suggests we can organise messy photons by trapping them into optical devices and cooling the light particles down until they become a super-photon. The device used is elegantly simple: a dye-filled microcavity, which consists of two mirrors facing each other and a tiny drop of organic dye between them. When photons enter the cavity, they start bouncing back and forth between the mirrors, repeatedly interacting with the dye molecules. With each interaction, they lose small amounts of energy, which ultimately leads to a super-photon conversion.
By modelling the behaviour of devices that trap light in a small region of space, the researchers noticed something truly interesting: it shares the same general properties as heat engines. In other words, the process is similar to generating energy using a steam engine, with disorganised light entering as input, coherent light exiting as output, and heat from the light acting as the hot source that powers the conversion process. This system would also need a cold reservoir to dump sacrificed energy that is not turned into coherent light.
Importantly, this engine does not ‘ignite’ with just any amount of heat from the hot source. It requires a specific temperature gradient to overcome internal losses, which is dictated by the Second Law of Thermodynamics. This threshold temperature would need to be higher when photon condensate is created from messy light rather than a laser, but the difference is insignificant. 
“The thing I’m interested in is making coherent light sources driven by sunlight or LEDs,” senior author of the study, Dr Paul Eastham, shared. “We can couple them with solar cells to improve energy efficiency.” Their idea lies in sticking a solar cell on the back of the optical device, resulting in a machine that would convert sun rays into coherent light first and then use it to generate electricity. However, Dr Eastham cautioned there is a long way until we see optical devices working in tandem with solar panels. “We need to do the actual experiment to show it could be done in the lab; we’re not even at this stage.”
Anyway, the goal of their future experiments goes well beyond “let’s make a better solar cell”. Rather, it’s about exploring “how energy could be extracted from sunlight” at a more fundamental level. Who knows, maybe we can harness free light from the Sun in entirely new ways?

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