New imaging technique captures every twist of polarized light

EPFL scientists have developed a new technique that allows researchers to look, with unprecedented sensitivity, how materials emit polarized light over time.

Light is not only bright or dark, colorful or simple. Its waves can also twist and turn, in a phenomenon called polarization. Think of the glasses you wear in a 3D film, which uses a light polarization to show each eye a slightly different image, creating the illusion of the depth.

Polarization is essential for future technologies, quantum computers with secure communication and holographic displays. Many materials emit light so as to code information in its polarization, as if we used the direction of light waves to send a message. Among these phenomena, there is a form known as the circular polarized luminescence (CPL), a special type of light emission produced by chiral materials where light waves spiral on the left or right during their trip.

Overcome the limits of traditional techniques

To unlock new applications, researchers must observe exactly how this polarization evolves over time. But so far, scientists have had to compromise because existing methods force a compromise between speed, sensitivity or a wide range of colors.

Standard CPL techniques are often slow, closely targeted or unable to collect low signals, especially when studying advanced materials with ephemeral or subtle polarization effects. These limitations have slowed down the quest to fully understand how chiral materials (given) interact with light.

Now, a team led by Professor Sascha Feldmann at the Laboratory for Energy Materials of EPFL has developed a technique of high sensitivity, high speed and resolved spectroscopy which captures the complete whole of polarization states (the so-called “vector stokes”).

The new technique does it through a large spectral window (400–900 nanometers), and at time intervals from nanoseconds to several milliseconds, all with a noise background as a thousand thousandth of the intensity of the polarized light emitted by a material. The new technique also captures linear and circular polarization signals at the same time, which helps to identify and correct polarization artifacts which often trigger other methods. Research is published in Nature.

A peak instrument

The team designed the instrument with simple and standard components, which makes it largely adoptable, and they share the complete optical diagrams and a collection of “non -obvious” error sources to open the land for others.

They used an electronic stopover camera and a set of polarization optics carefully designed to record the full vector stokes in real time, depending on the light emission changes from different types of molecules which have a strong and weak polarized luminescence. By registering the full polarization fingerprint, the new configuration can discover the details that other approaches are lacking.

The new approach succeeded in polarization changes in materials that had never been followed in detail before. It has reproduced the reference results for well -studied molecules, and it revealed a dynamic previously invisible in organic transmitters and complex systems where light emission occurs at fast and slow time ladders.

The technique has also exhibited subtle polarization artifacts – signals the signals that traditional measures often confuse with real effects – ranging from researchers to avoid current traps.

With its combination of high sensitivity, wide spectral coverage and Nanosecond temporal resolution, the technique opens an unprecedented window on the field of polarization dynamics in the excited state and the rupture of symmetry. Scientists can now observe these processes in real time, accelerating the design and development of chiral transmitters, quantum materials and advanced optoelectronic devices.

The team also rendered its automation plans and algorithms in order to democratize the field and help accelerate discoveries in the world.