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.