Coherence of Raman light arises from disorder

February 13, 2017
Credit: National Research Council of Italy

Light propagation in disordered materials is a topic of great interest for the scientific community, with applications in the fields of photonics and renewable energies and the discovery of fascinating new phenomena related to wave physics.

A team of researchers with different expertise in the fields of optical spectroscopy, photonics and material science has reported on a new physical effect demonstrating the coherent nature of spontaneous Raman-. The work, recently published in Nature Photonics with the title "Coherent Backscattering of Raman Light," paves the way to the development of a new research field on complex photonics systems exploiting both elastic (Rayleigh) and inelastic (Raman) scattered light.

"A dense forest of ultrathin silicon wires arranged in a disordered fashion, in which light waves bounce back and forth countless times before coming out, is the material that allowed us to reveal this new phenomenon. What we observed as a macroscopic physical effect is the coherence between Raman scattered light waves, which typically occurs on the scale of nanometers, given by the phonon coherence length," says the paper by Barbara Fazio (CNR-IPCF, Messina), Matteo Galli (University of Pavia), Francesco Priolo (University of Catania and CNR-IMM) and Diederik Wiersma (LENS, University of Firenze), who led the study.

The physical phenomenon is known as coherent backscattering of light, which has long been observed and studied only for elastically scattered light and now is demonstrated also for inelastic light scattering (Raman). Coherent backscattering of light is a very subtle interference effect occurring in disordered scattering media (such as semiconductor powders or micro-particle suspensions like milk or fog), in which wave coherence is preserved even after a very large number of random scattering events, eventually manifesting as a maximum of interference in the exact backscattering direction. The team of researchers demonstrated that this experimental evidence surprisingly survives also for inelastic light scattering, such as the spontaneous Raman process, as long as the optical information of the propagating wave is retained. In this kind of inelastic scattering event, loses a small part of its energy by changing wavelength (colour). Its phase coherence, however, is preserved for a very short time, thus making interference between Raman scattered waves still possible.

The observed maximum of interference in the exact backscattering direction is therefore a signature of the coherent nature of individual Raman scattering processes. To date, evidence on the coherence properties of Raman has been reported only by looking at the nanoscopic scale, through complex near-field experiments making use of very sharp tips or through ultra-fast time resolved techniques. This time, however, the researchers did not rely on complex experiments or advanced techniques. The combination of the unique structural properties of a silicon-based nanomaterial, an accurate experimental procedure and, above all, effective brainstorming and synergy between research groups were the only ingredients for the observation of a new unexpected physical phenomenon, which opens the way to new and important discoveries.

Explore further: Lattice of nanotraps and line narrowing in Raman gas

More information: Barbara Fazio, Alessia Irrera, Stefano Pirotta, Cristiano D'Andrea, Salvatore Del Sorbo, Maria Josè Lo Faro, Pietro Giuseppe Gucciardi, Maria Antonia Iatì, Rosalba Saija, Maddalena Patrini, Paolo Musumeci, Cirino Salvatore Vasi, Diederik S. Wiersma, Matteo Galli and Francesco Priolo, 10.1038/nphoton.2016.278

Related Stories

Lattice of nanotraps and line narrowing in Raman gas

February 9, 2017

Decreasing the emission linewidth from a molecule is one of the key aims in precision spectroscopy. One approach is based on cooling molecules to near absolute zero. An alternative way is to localize the molecules on subwavelength ...

Amplifying our vision of the infinitely small

December 2, 2013

Richard Martel and his research team at the Department of Chemistry of the Université de Montréal have discovered a method to improve detection of the infinitely small. Their discovery is presented in the November 24 online ...

Nanoparticle imaging: A resonant improvement

October 28, 2011

Raman spectroscopy is a powerful technique for analyzing atomic structure based on the inelastic scatter of light from molecules, with diverse applications including medical imaging and chemical sensing. Researchers have ...

Recommended for you

Two teams independently test Tomonaga–Luttinger theory

October 20, 2017

(Phys.org)—Two teams of researchers working independently of one another have found ways to test aspects of the Tomonaga–Luttinger theory that describes interacting quantum particles in 1-D ensembles in a Tomonaga–Luttinger ...

Using optical chaos to control the momentum of light

October 19, 2017

Integrated photonic circuits, which rely on light rather than electrons to move information, promise to revolutionize communications, sensing and data processing. But controlling and moving light poses serious challenges. ...

Black butterfly wings offer a model for better solar cells

October 19, 2017

(Phys.org)—A team of researchers with California Institute of Technology and the Karlsruh Institute of Technology has improved the efficiency of thin film solar cells by mimicking the architecture of rose butterfly wings. ...

Terahertz spectroscopy goes nano

October 19, 2017

Brown University researchers have demonstrated a way to bring a powerful form of spectroscopy—a technique used to study a wide variety of materials—into the nano-world.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

swordsman
not rated yet Feb 13, 2017
Atomic phonons produce electromagnetic waves, since atoms consists of electron and protons. When an electron moves through space, it creates a radiation electromagnetic wave similar to that of a transmitting antenna. Planck's original quantum theory was based on this principle. The change that occurs when the electrons change from one stable state to another produces coherent electromagnetic waves that is known as Rydberg wavelengths/frequencies (Borh).

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.