Setup for two experiments demonstrating phonon-enhanced nonlinearity in hBN, in transmission geometry. an experimental setup for THG experiments. Detection is performed using PbS and MCT detectors, a lock-in amplifier, and boxcar averaging. b Experimental setup for pump-probe FWM experiments. The delay is controlled by a mechanical delay stage with a pitch less than 1 µm. Both the pump and probe are focused on the sample with a reflective lens with a numerical aperture of 0.5. Detection is performed with a silicon photomultiplier tube and a lock-in amplifier. Credit: Natural communications (2023). DOI: 10.1038/s41467-023-43501-x
Columbia University engineers and Max Planck Theoretical Collaborators for the Structure and Dynamics of Matter have discovered that combining laser light with crystal lattice vibrations can improve the nonlinear optical properties of a material Layered 2D. The research is published in the journal Natural communications.
Cecilia Chen, who holds a doctorate in engineering from Columbia. student and co-author of the recent paper, and her colleagues in Alexander Gaeta’s quantum and nonlinear photonics group, used hexagonal boron nitride (hBN). hBN is a 2D material similar to graphene: its atoms are arranged in a repeating honeycomb-like pattern and can be peeled into thin layers with unique quantum properties. Chen noted that hBN is stable at room temperature and its constituent elements – boron and nitrogen – are very light. This means they vibrate very quickly.
Atomic vibrations occur in all materials above absolute zero. This movement can be quantified into quasiparticles called phonons with particular resonances; in the case of hBN, the team was interested in the optical phonon mode vibrating at 41 THz, corresponding to a wavelength of 7.3 μm, which is located in the mid-infrared regime of the electromagnetic spectrum.
While mid-IR wavelengths are considered short, and therefore high energy, in the picture of crystal vibrations they are considered very long and low energy in most optical research with lasers, where the overwhelming majority of experiments and studies are carried out in the visible. at a near infrared range of approximately 400 nm to 2 um.
When they tuned their laser system to the hBN frequency corresponding to 7.3 μm, Chen and his fellow Ph.D. student Jared Ginsberg (now a data scientist at Bank of America) and postdoc Mehdi Jadidi (now a team leader at quantum computing company PsiQuantum), were able to coherently and simultaneously drive the crystal’s phonons and electrons hBN to efficiently generate new optical frequencies. of the medium, an essential objective of nonlinear optics. Theoretical work carried out by Professor Angel Rubio’s group at Max Planck helped the experimental team understand their results.
Using commercially available benchtop mid-infrared lasers, they explored the nonlinear optical process mediated by four-wave mixing phonons to generate light near the even harmonics of an optical signal. They also observed a 30-fold increase in third harmonic generation compared to what is obtained without exciting the phonons.
“We are excited to show that amplifying the natural motion of phonons with laser control can enhance nonlinear optical effects and generate new frequencies,” Chen said. The team plans to explore how they could modify hBN and similar materials using light in their future work.
More information:
Jared S. Ginsberg et al, Phonon-enhanced nonlinearities in hexagonal boron nitride, Natural communications (2023). DOI: 10.1038/s41467-023-43501-x
Provided by Columbia University School of Engineering and Applied Sciences
Quote: Engineers combine laser light with crystal lattice vibrations to improve optical properties of 2D material (December 27, 2023) retrieved December 27, 2023 from
This document is subject to copyright. Apart from fair use for private study or research purposes, no part may be reproduced without written permission. The content is provided for information only.
