Record number of beams by a grating for future stardust cameras

Astronomers need terahertz cameras to study the atoms in the interstellar medium. They need gratings for this with a local oscillator that uses multiple beams. Yuner Gan, a PhD student at SRON and RuG, has now demonstrated a local oscillator concept with a record number of 81 beams, published in Optics Express.

If you want to investigate atoms and molecules in the interstellar medium, you need to look at a specific type of infrared light: terahertz radiation. Light with terahertz frequencies falls in the wavelength domain which contains the fingerprints of various substances.

Multiple beams

Astronomers need a special camera based on so-called heterodyne receivers to pick up this specific radiation. These receivers mix a terahertz signal from space with its own signal from a local oscillator to generate a signal at microwave frequency, making it easier to handle for scientists. This approach allows to capture the atomic and molecular fingerprints at a high spectral resolution of at least one million. Space missions at terahertz frequencies often have insufficient room for a separate oscillator for each pixel, so they need a local oscillator with multiple beams.

High efficiency

Yuner Gan, a PhD student at SRON Netherlands Institute for Space Research and University of Groningen, has now demonstrated a local oscillator with 81 beams, while the current state-of the art is about ten beams, as used in NASA's upcoming GUSTO balloon mission. Supported by an international team, she has developed a grating which splits a single 3.8 terahertz beam signal into 81 beams at a high efficiency of about 95 percent. The 81 beams are relatively uniform, which is crucial for the performance of the camera.

Publication

Yuner Gan, Behnam Mirzaei, Jose R.G. Silva, Ali Khalatpour, Qing Hu, Christopher Groppi, Jose V. Siles, Floris van der Tak, and Jian-Rong Gao, '81 supra-THz beams generated by a Fourier grating and a quantum cascade laser', Optics Express