Andreas Wicht Abstract

Thanks to the recent advances in optical metrology, quantum optics precision measurements have reached a level of precision and accuracy which strongly suggests that quantum optical sensors will soon play a key role in a large number fields as diverse as fundamental physics, inertial navigation, geophysics and prospection, and precision time keeping, just to name a few.

Quantum sensors will provide the means to test at an unprecedented level the equivalence principle and other aspects of Special and General Relativity, to investigate fundamental decoherence in quantum physics, or may even be used to observe gravitational waves. The best optical clocks already outperform the microwave time standards. Atom interferometry may be used to carry out very precise and accurate measurements of the local value of the gravitational acceleration and of its gradient. Atom interferometers may also be used for inertial navigation. Some of these applications demand for a space borne operation, either because space is (supposed to be) a less noisy environment or/and because some of the effects under consideration (e.g. tests of General Relativity) are stronger under conditions, that can be met only in space. The current generation of quantum sensors requires an optics lab-kind of experimental environment. At the time being lots of efforts are therefore put into advancing the technology readiness level of the quantum sensor technology at German national but also at European level. The main focus lays on the development of the corresponding laser technology.

With the GaAs-technology available at the Ferdinand-Braun-Institute (FBH), diode lasers can be developed and fabricated within the wavelength range from 630 nm to 1100 nm. Activities include the development of "simple" ridge-waveguide laser chips, distributed feedback (DFB)-lasers, distributed Bragg reflector (DBR) lasers, tapered power amplifiers and monolithic master oscillator power amplifier (MOPA) systems as well as of broad area (BA) lasers that deliver more than 50 W of output power from a single emitter. The FBH has recently also started to micro-integrate laser chips, micro-optics and electronics to provide complete laser systems that are already space qualified or can be space qualified in the near future. Micro-integration concepts include extended cavity diode lasers, hybrid MOPAs and laser systems that already include second harmonic generation (SHG) units. The latter provides the means to access the wavelength range below 630 nm with micro-integrated lasers based on III/V semiconductor technology.

In this talk I will give an overview about the activities ongoing at FBH, that are aimed at the development of micro-integrated diode laser systems for precision quantum optics experiments in space, and that are part of the national initiative to support quantum sensor technology development for space applications. In a first step a Rubidium Bose-Einstein condensate (BEC) will be produced and a matter wave interferometer will be demonstrated by a national consortium onboard a sounding rocket by the end of 2013. Follow ups will aim at deploying quantum sensors onboard the ISS or on dedicated satellite missions. The ultimate goal is to perform a quantum test of the equivalence principle based on the analysis of the relative acceleration of Rubidium and Potassium atoms in free fall. To this end high power, narrow linewidth, micro-integrated diode laser systems are currently being developed by FBH that provide an output power in excess of 1 W at 780 nm with an intrinsic linewidth of a few 10 kHz (hyprid integrated DFB-MOPAs). With a DBR-MOPA emitting more than 1 W of optical power at 1060 nm an intrinsic linewidth of 3.6 kHz has been demonstrated very recently, a linewidth unrivaled so far for diode lasers. Applications like Raman beam generation for atom interferometers pose even stronger requirements on the laser linewidth. For these applications, extended cavity diode lasers are micro-integrated that omit any movable parts. These systems provide an out power in excess of 50 mW with an intrinsic linewidth of a few kHz, a 3 dB linewidth significantly smaller than 50 kHz (10 µs time scale) and a tuneability of 100 GHz. As a partner of a European consortium the FBH also develops micro-integrated extended cavity laser systems that include a miniature Rubidium cell and a micro-integrated modulation transfer spectroscopy setup for absolute laser frequency stabilization. Related work is aiming at the development of a diode laser based frequency comb for optical metrology in the 767 nm to 780 nm range.