Visible-light emission from carbon fiber induced by 159-GHz millimeter-wave irradiation

Abstract

The direct visualization of millimeter-wave radiation is crucial for the development of radiation sources and their applications. In this study, we experimentally determined the minimum incident energy density required to induce visible-light emission from a single polyacrylonitrile-based carbon fiber by using a 159-GHz gyrotron as the radiation source. A simple nitrogen-filled carbon-fiber holder was developed to prevent oxidative burnout of the carbon fiber. As a result, the minimum incident energy density was estimated to be 0.63 mJ/mm2 at 159 GHz. This value is approximately one order of magnitude lower than that predicted from the specific heat of carbon. In addition, emission spectra were obtained over the wavelength of 340–640 nm, showing continuous emission, and the brightness temperature was estimated to be 2100–2300 K at an incident energy density of approximately 2.5–3.2 mJ/mm2. These findings open a new route to the direct visualization of millimeter-wave radiation and carbon fibers.