Scientists in Finland have demonstrated the first fully solution-processed solid-state polariton laser, potentially opening a simpler and cheaper path toward advanced laser and photonic technologies.
Researchers at the University of Turku, working with colleagues at the University of Eastern Finland, created the entire tiny laser structure by applying materials from liquid solutions.
The achievement is significant because advanced solid-state lasers usually require complicated manufacturing methods, including vacuum-based processes that can be expensive and energy intensive.
The new research, published in Nature Communications, suggests that much simpler manufacturing techniques can still produce materials with the extremely high optical quality required for advanced laser physics.
The device is known as a microcavity, a microscopic structure containing mirrors that trap light between them. In the new system, both these mirrors and the organic material that produces light were made using a technique called spin coating.
During spin coating, a small amount of liquid material is placed onto a surface that spins rapidly. The spinning action spreads the liquid into a very thin and even layer.
By repeating this process, researchers can build complex structures without relying on vacuum deposition.
But the new device is more than an easier-to-manufacture conventional laser.
Its high-quality microcavity creates conditions in which light interacts extremely strongly with molecules in the organic material. Under these conditions, light and matter effectively mix together, producing unusual hybrid states known as polaritons.
These polaritons have properties of both light and matter. Their collective behavior allows the device to produce intense, laser-like emission, creating what scientists call a polariton laser.
According to the researchers, demonstrating this behavior in a device made completely through solution processing could make polariton research more accessible to laboratories without expensive manufacturing equipment.
The scientists also discovered surprising behavior when they increased the amount of energy used to drive the device.
At lower levels, light was mainly emitted from the center of the area being excited. But under stronger driving, the light began moving outward, eventually producing a visible ring-shaped pattern.
Importantly, the change was reversible. Researchers could also control how strongly the ring appeared by adjusting the optical properties of the microcavity.
The unusual pattern provides scientists with a way to observe interactions between polaritons on a relatively large and easily visible scale. This could help researchers investigate nonlinear effects, in which a system’s response changes dramatically as the amount of energy supplied to it increases.
The researchers believe their manufacturing approach could eventually make organic lasers and other advanced light-based technologies easier and less expensive to produce.
Solid-state lasers already play important roles in telecommunications, sensing, medical technologies and data storage. Solution processing could potentially allow some future photonic devices to be manufactured more efficiently and on larger scales.
One longer-term goal is the development of organic lasers powered directly by electricity rather than external light sources.
For now, the new device shows that sophisticated interactions between light and matter do not necessarily require equally sophisticated manufacturing. Sometimes, advanced laser technology may be built one thin liquid-coated layer at a time.
