Sebastian Rabien

Dr. Sebastian Rabien
Max-Planck Institut für extraterrestrische Physik
               Giessenbachstr, 85748 Garching, Germany              
phone: +49_89300003277
email: srabien(a)


    My Current Projects at MPE

The ARGOS project at the Large Binocular Telescope

The ARGOS project has equipped the Large Binocular Telescope (LBT) in Arizona with a multi laser guide star and adaptive optics facility. It has been designed, built and is currently under commissioning phase by an international consortium assembled out of Institutes from Italy, the United States and Germany, led by MPE and me  as principal investigator (PI). ARGOS launches a constellation of six laser guide stars, three above each of LBT's primary mirrors. Detecting the 'Rayleigh' laser guide stars  with a gated wavefront sensor, enables us to correct the atmospheric distortions over a wide field of view. Each of the LUCI imagers and spectrographs can thus be fed with sharpened images, allowing a strongly enhanced performance. To the right the LBT can be seen with the ARGOS lasers in operation.
More information can be found at:
The MPE ARGOS webpages


First Images with ARGOS

To the left a J, H-band composition image of NGC 6384 is shown, taken with laser guide star ground layer adaptive optics correction. The resolution in H-band amounts to ~0.22 arcsec close to the central TT star, and is fairly homogenic over the full field of view. With ARGOS coming online, astronomical observations at LBT can be conducted much faster due to the enhanced image sharpness.

First Light Image with ARGOS

In late 2014 we have been able to close the adaptive optics loop for the first time on the laser guide stars. First ever an 8.4m telecope has been corrected with a laser based GLAO adaptive optics system. The spatial resolution increase from seeing limited to corrected amounts to 2-3, well in agreement with the calculated expectations. Applying this factor to multi object spectroscopy of high distant objects in the universe, will allow these observations to be carried out at LBT in a fraction of time as required nowadays. 


thin film laser cut MOS mask
In situ cryogenic MOS mask generation

multi object spectroscopy allows to measure the spectrum of many objects in the telescopes field of view at the same time. To select the objects from which to measure the spectrum, requires a selector mask in the instrument. Since infrared spectrographs are operated under vacuum at cryogenic temperatures, mask handling and exchange is rather complex.
Currently we are developing novel methods for in-situ mask generation. Based on laser ablation of thin films at 77K or thin foil cutting and handling. This will facilitate infrared MOS instrument operation greatly and enable advanced observing programs.

Former Instrumentation Projects

parsec_amplifier Laser_Fringes_on_M2
ALFA one of the first astronomical adaptive optics systems with laser guide star. Being located at the Calar Alto observatory in Spain, ALFA has been using a 3W cw dye laser to create a laser guide star in the earth sodium layer.
PARSEC: the laser system for the VLT Laser guide star facility. Being developed by ma in the framework of my PhD thesis, it consisted of a master laser power amplifier, based on dye technology. With 5 green lasers pumping the system, it routinely delivered 13W single frequency cw laser light at the Sodium D2 transition and has shown a maximum output power of 24W. The LGSF has been in operation at Paranal for several years.
GRAVITY: combining the light from all four UT telescopes at the VLT interferometrically allows to adress fundamental scientific questions. Gravity will measure the position of flares in the galactic center with µarcsec precision, thus probing space time in the vicinity of a super massive black hole. The image shows 1908nm laser fringes at the secondary for the path length metrology with nm precission.



Last edited by Sebastian Rabien: 21 May 2015 - These pages are subject to the standard MPE disclaimer