Visible light is electromagnetic radiation within the electromagnetic spectrum that can be perceived by human eyes. The light we see is a mere fraction of the wavelengths of light that exists. Light ranges from the longer wavelength Far Infrared (FIR) to shorter wavelength Extreme ultraviolet. Infrared (IR) and Ultraviolet (UV) lights have many industrial and scientific applications.
Within the ultraviolet range is a subset of wavelength known as Vacuum Ultraviolet light (VUV), named so because they can pass through a vacuum but easily absorbed by the air. Scientists are particularly interested in the VUV of wavelength range between 120 to 200 nanometers (nm) as it has multiple scientific and medical applications. They can be used in spectroscopy to study the physical and chemical properties of various materials, including biological materials.
Today, VUV lights are produced using particle accelerators and laser-driven plasmas. These are complex, expensive, and less scalable, and they provide VUV that are linear polarized and not circular polarized, which has applications in the research field.
Assistant Professor Kuniaki Konishi from the Institute for Photon Science and Technology at the University of Tokyo and his team have created a simple device to convert circularly polarized visible laser light into circular polarized VUV, twisted in the opposite direction. They created a photonic crystal dielectric nanomembrane (PCN) consisting of a sheet made from an aluminum oxide-based crystal (?-Al2O3) that is only 48 nm thick. It sits atop a 525 micrometer-thick sheet of silicon with 190 nm-wide holes cut into it 600 nm apart.
When pulses of circularly polarized blue laser light with a wavelength of 470 nm shine down these channels in the silicon, the PCN twists them in the opposing direction and reduces their wavelengths to 157 nm, which is well within the range for spectroscopy. Similar methods demonstrated earlier using metal-based film produced VUV in less useful wavelengths, and the metal film rapidly degraded in the presence of laser. The new PCN membrane can survive repeated bombardment by laser light without degrading, making it ideal for spectroscopy.
Short pulses of circular polarized VUV is required to observe fast or short-lived physical phenomena at the submicrometer scale that are otherwise impossible to see. Phenomena include behaviors of electrons and biomolecules. VUV produced by this method can be useful to researchers in medicine, life sciences, molecular chemistry, and solid-state physics.
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