Diode lasers for precision quantum optics experiments in space
FBH has developed micro-integrated master-oscillator power-amplifier (MOPA) laser and extended cavity diode laser (ECDL) modules for experiments on Rubidium Bose-Einstein condensates on board a sound rocket to be launched in 2013. The MOPA concept is based on optimizing a low power distributed feedback (DFB) or distributed Bragg reflector (DBR) for stable narrow linewidth emission and amplification of its radiation by means of a separate power amplifier chip. The ECDL concept uses optical feedback from an external optical grating. This way, large cavity lengths can be realized which provide a reduction of the frequency noise linear spectral density by 1 to 2 orders of magnitude with regard to monolithic lasers.
Hybrid micro-integration technology is used to integrate laser chips, optics, and electronics on an aluminum nitride ceramic body that takes a volume of only 8 x 2.5 x 1.5 cm3. This amounts to a reduction of the form factor by 3 orders of magnitude with respect to commercial systems. Both module types further omit any moveable parts so that the requirements on mechanical stability for space applications can be met. These MOPA modules have already successfully passed vibration test at 8 gRMS that simulate the mechanical stress of a sounding rocket launch. Further tests are pending.
The MOPA modules provide an optical power in excess of 1 W at 780.24 nm. Depending on the laser chip used as a master oscillator, a short term (10 µs) emission linewidth below 1 MHz and an intrinsic linewidth as small as a few 10 kHz can be realized. The ECDL provides an output power of typically 50 mW with a short term linewidth of well below 100 kHz and an intrinsic linewidth of a few kHz only. It is hence suited for applications with the most stringent requirements on spectral stability. Coarse frequency tuning is realized by thermally tuning the optical grating which provides a tuning range of approximately 80 GHz.
MOPA and ECDL technology can be transferred to other wavelengths in the 650 nm to 1100 nm wavelength range. It is also considered for the realization of lasers for portable optical clocks.
E. Luvsandamdin, G. Mura, A. Wicht, A. Sahm, S. Spießberger, H. Wenzel, G. Erbert and G. Tränkle, "fbh-berlin/english/ver11/pub63.htm _blank internal-url-new-window>Micro-integrated ECDLs for precision spectroscopy in space", Int. Conf. on Space Optical Systems and Applications (ICSOS 2011), Santa Monica, USA, May 11-13, pp. 383-385 (2011).
Ch. Kürbis, A. Kohfeldt, E. Luvsandamdin, M. Schiemangk, S. Spießberger, A. Wicht, A. Peters, G. Erbert, G. Tränkle, "Mikrointegrierte Lasersysteme für die höchstauflösende Atomspektroskopie und die kohärente Nachrichtenübertragung im Weltraum", 60. Deutscher Luft- und Raumfahrtkongress, Bremen, Germany, Sep 27-29 (2011).