Terahertz laser local oscillator for SOFIA

Detecting atomic oxygen in space

The Stratospheric Observatory for Infrared Astronomy (SOFIA) offers unique possibilities for exploring the Universe. With the 2.7-metre telescope integrated into a modifed Boeing 747SP, astronomical observations in the infrared and terahertz wavelength ranges can largely be performed without the disturbing influence of the atmosphere.

The GREAT spectrometer and its enhanced version upGREAT (German Receiver for Astronomy at Terahertz Frequencies) form one of the monitoring instruments used on SOFIA. They are so-called heterodyne spectrometers that measure the sky simultaneously at two frequencies in the range of 1.25 to 5 terahertz with high resolution. With the resulting precise measurements of the line shape of atomic or molecular emission and absorption lines, researchers can determine the dynamic conditions of an astronomical object.

The local oscillator laser shown here is an integral part of the high-resolution spectrometer for measurements at 4.7 terahertz. It allowed the routine observation of the astronomically important fne structure line of atomic oxygen for the frst time. The atomic oxygen line at a frequency of 4.7 terahertz is an important source of information for researchers to better understand the formation of stars. Ground-based observatories cannot detect these because of water absorption in the atmosphere. The SOFIA local oscillator laser is the first of its kind in the world. The instrument is a high-precision frequency source based on novel terahertz quantum cascade lasers developed by the DLR Institute of Optical Sensor Systems in collaboration with the Paul Drude Institute for Solid State Electronics. It consists of several layers of semiconductor structures that must be cooled down to temperatures below -220 degrees Celsius. The whole system must be suffciently stable and powerful, while being robust enough for everyday use in the airborne observatory.

German Aerospace Center (DLR)

Stephanie Kaufhold · E-Mail: stephanie.kaufhold@dlr.de · DLR.de/en