Reading Between the OH Lines
Near-infrared emission from OH radicals in the Earth’s mesosphere is composed of hundreds of narrow emission lines. This emission severely degrades astronomical observations by increasing the sky luminosity and its associated Poisson noise. Many attempts to filter these lines have been made using various optical technologies, which will be reviewed and compared. A closer look will be given to Volume Bragg Grating technology, which can be used as extremely narrow line reflectors or diffractors. Early results will be discussed in the context of the substantial evolution of this technology over the last few years.