Light poses a fundamental challenge because it behaves both as a particle and a wave. Each wave has a characteristic wavelength that defines its natural scale. In the case of visible light, this wavelength is typically a few hundred nanometers, while infrared light can extend to a micrometer or more. This leads to a key question: is it possible to confine light within structures smaller than its own wavelength?

Figure 1. Light Confined in a Layer 1,000× Thinner Than Human Hair.

The research team has demonstrated that this is indeed achievable. They designed a structure capable of trapping infrared light within an ultra-thin layer just 40 nanometers thick (approximately 0.00004 millimeters or 0.0000016 inches). This breakthrough was achieved using a subwavelength grating made from molybdenum diselenide (MoSe₂), as reported in ACS Nano. Figure 1 shows Light Confined in a Layer 1,000× Thinner Than Human Hair.

What Is a Subwavelength Grating?

A subwavelength grating is a specialized diffraction structure made up of tightly spaced parallel lines. Like a prism, it can bend and split light, but when the spacing between these lines is smaller than the light’s wavelength, the grating behaves almost like a perfect mirror while also trapping light in an extremely small space.

Earlier designs, using materials such as silicon, gallium arsenide, or gallium nitride, required thicknesses of several hundred nanometers to function effectively. When made thinner, they lost their ability to confine light.

To address this limitation, researchers turned to a material with a much higher refractive index—meaning it slows down light more significantly. Molybdenum diselenide (MoSe₂) proved especially effective. While light slows by about 1.5 times when moving from air into glass and about 3.5 times in silicon or gallium arsenide, it slows by roughly 4.5 times in MoSe₂. This property enabled the creation of a grating only a few dozen nanometers thick—over a thousand times thinner than a human hair.

Nonlinear Effects and Light Transformation

MoSe₂ offers additional advantages beyond light confinement. Similar to graphene, it has a layered structure, but unlike graphene, it behaves as a semiconductor. It also exhibits nonlinear optical properties, such as third harmonic generation.

In this phenomenon, three photons merge to form a single photon with triple the frequency. This allows infrared light to be converted into blue light, as three lower-energy infrared photons combine into one higher-energy photon in the blue spectrum. According to findings reported in ACS Nano, the strong confinement of light within the MoSe₂ grating enhances this effect by more than 1,500 times compared to a flat layer of the same material.

A Breakthrough in Fabrication Methods

Another important aspect of the study is how the material was produced. Traditionally, thin MoSe₂ layers were obtained through exfoliation—the same tape-based method used for graphene. While simple, this approach is unreliable and produces very small samples, typically around ten square micrometers—far too limited for practical applications like photonic integrated circuits.

To overcome this challenge, the researchers employed molecular beam epitaxy (MBE), a well-established technique for fabricating semiconductor layers. This marks one of the first successful applications of MBE to materials like MoSe₂.

Using this method, the team produced uniform MoSe₂ layers spanning several square inches, all with a consistent thickness of just 40 nanometers (approximately 0.00004 millimeters or 0.0000016 inches). This results in an extreme aspect ratio of about 1:1,000,000. For comparison, a standard A4 sheet of paper has an aspect ratio of roughly 1:2000.

Source:NEW ATLAS

Cite this article:

Priyadharshini S (2026), Scientists Confine Light Within a Layer 1,000 Times Thinner Than a Hair, AnaTechMaz, pp. 370