New Method - Observing how materials emit polarized light

Many materials emit light in ways that encode information in its polarization. According to researchers at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, polarization is key for future technologies, from quantum computers to secure communication and holographic displays.
Among such phenomena is a form known as circularly polarized luminescence (CPL), a special type of light emission produced by chiral materials, in which light waves spiral either left or right as they travel.

Standard CPL techniques are often slow, narrowly focused, or unable to pick up faint signals, says EPFL, especially when studying advanced materials with fleeting or subtle polarization effects. These limitations have slowed the quest to fully understand how chiral materials interact with light.

Now, a team led by Professor Sascha Feldmann at EPFL’s Laboratory for Energy Materials has developed a high-sensitivity, broadband, time-resolved spectroscopy technique that captures the complete set of polarization states (the so-called "Stokes vector"). The work, including shared blueprints, is described in Nature.

Wide window

The new technique does this across a wide spectral window (400–900 nm), and at time intervals ranging from just nanoseconds up to several milliseconds, all with a noise floor as low as one ten-thousandth the intensity of the polarized light being emitted by a material. The new technique also captures linear and circular polarization signals at the same time, which helps identify and correct for polarization artifacts that often disrupt other methods.

The EPFL team says it designed the instrument “with straightforward, off-the-shelf components, making it widely adoptable.” They are sharing the full optical schematics and a compendium of “non-obvious” error sources to open the field up for others.
They used an electronically-gated camera and polarization optics to record the full Stokes vector in real time, tracking changes in light emission from different types of molecules that feature both strong and weak polarized luminescence. By recording the complete polarization fingerprint, the new set up can uncover details that other approaches miss, says EPFL.

The new approach successfully captured polarization changes in materials that had never been tracked in such detail before. It reproduced benchmark results for well-studied molecules, and it revealed previously unseen dynamics in organic emitters and complex systems where light emission happens on both fast and slow timescales.

With its combination of high sensitivity, wide spectral coverage, and nanosecond time resolution, the technique is said to open an unprecedented window onto the realm of excited-state polarization dynamics and symmetry-breaking. The team has also made their blueprints and automation algorithms public in an effort to democratize the field and help speed up discoveries worldwide.

Source: optics.org