Stable, fibre-coupled ultra-low-expansion cavities with good optical access for cryogenic experiments in space

Short Description

Starting point / motivation

Advances in matter-wave interferometry and quantum optomechanics promise allowing novel fundamental tests of physics at the interface between quantum physics and gravity. Because ground-based experiments may soon face principal limitations with respect to such tests, the mission proposal MAQRO suggests using the unique environment of space and harnessing recent advances in space technology to overcome those limitations.

Contents and goals

To realize this mission, several core technologies need further development. For example, one of the central elements of MAQRO is a high-finesse optical cavity on an optical bench mounted outside the spacecraft in a cryogenic environment.


In the preceding project MAQROsteps, we could show that it is possible using space-proof adhesives to glue a stable cavity assembly that could be used for space-based experiments.

However, this was only shown for room temperature. Realizing a stable adhesively bonded cavity for a cryogenic environment in space still holds several challenges:

  • optical beams on the optical bench of MAQRO cannot be realigned – they have to be stably coupled from glass fibres into the cavity and back again.
  • the original alignment of the optical elements will be done at room temperature but the alignment later has to operate at cryogenic temperatures.
  • the space-proof adhesive-bonding technology to be used has not been tested for cryogenic temperatures so far.

Expected results

In the proposed project ULE-Cavity-Access, we want to meet these challenges. We will develop cavity designs where light is coupled directly from fibres into a stably bonded cavity and back again. We will test these designs also at cryogenic temperatures, and we will perform thermal simulations to investigate the behaviour of the optical bench of MAQRO when cooled to cryogenic temperatures and adapt the design if necessary.

Our results will increase the TRL of core elements of MAQRO, the TRL of adhesive-bonding technology for optical elements and the TRL of high-finesse optical cavities with good optical access for space applications in general.

Project Partners


Austrian Academy of Sciences

Contact Address

Austrian Academy of Sciences
Dr. Rainer Kaltenbaek
Boltzmanngasse 3
A-1090 Vienna