Scientists and engineers from Columbia University and the Max Planck Institute for the Structure and Dynamics of Matter have teamed up to explore the fascinating world of 2D materials and their nonlinear optical properties. In a recent study published in the journal Nature Communications, they discovered that by combining laser light with crystal lattice vibrations, they were able to enhance the nonlinear optical effects of a layered 2D material. This groundbreaking research opens up new possibilities for manipulating and harnessing light in exciting ways.
At the forefront of this innovative study is hexagonal boron nitride (hBN), a 2D material with a similar structure to graphene. The unique arrangement of atoms in hBN forms a honeycomb-shaped pattern, which gives it remarkable quantum properties. Unlike graphene, hBN is stable at room temperature and consists of extremely lightweight boron and nitrogen atoms that vibrate quickly.
The researchers were particularly interested in the optical phonon mode of hBN, which vibrates at a frequency of 41 THz, equivalent to a wavelength of 7.3 µm in the mid-infrared range. Traditionally, laser experiments and studies focused on the visible to near-infrared spectrum, ranging from approximately 400 nm to 2 µm. Mid-IR wavelengths, although considered high energy, are considered long and low energy in the context of crystal vibrations.
To investigate the effect of laser-light pairing with hBN’s lattice vibrations, the research team tuned their laser system to match the frequency of hBN’s optical phonon mode. By doing so, they were able to simultaneously drive both the phonons and electrons of the crystal, leading to the efficient generation of new optical frequencies. This observation is a significant milestone in the field of nonlinear optics.
The experimental findings were complemented by theoretical work conducted by Professor Angel Rubio’s group at the Max Planck Institute. Rubio’s team provided invaluable insight and understanding of the results obtained from the experiments. Their theoretical models and calculations helped shed light on the underlying mechanisms and confirmed the enhanced nonlinear optical effects achieved by laser-light pairing with hBN’s lattice vibrations.
One of the most exciting findings of this study was the generation of light close to even harmonics of an optical signal using a four-wave mixing process mediated by phonons. This process resulted in a remarkable 30-fold increase in third-harmonic generation compared to experiments without exciting the phonons. These results demonstrate the immense potential of amplifying natural phonon motion with laser driving to create new frequencies and enhance nonlinear optical effects.
The researchers involved in this study are thrilled about the possibilities that lie ahead. They plan to further explore how they can modify hBN and other similar materials using light in future projects. By tailoring the properties of these 2D materials, it may be possible to unlock even more enhanced nonlinear optical effects and pave the way for new advancements in photonics, quantum computing, and other related fields.
The collaboration between engineers at Columbia University and theoretical researchers at the Max Planck Institute has led to a groundbreaking discovery in the realm of laser-light pairing with crystal lattice vibrations. By harnessing the power of hexagonal boron nitride, the team has demonstrated the exciting potential of enhancing nonlinear optical effects and generating new frequencies. This study not only opens up new avenues for manipulating light but also paves the way for future advancements in various scientific and technological fields.