We present our the construction of an atom interferometer for inertial sensing in microgravity, as part of the I.C.E. (Interferometrie Coherente pour l’Espace) collaboration. On-board laser systems have been developed based on fibre-optic components, which are insensitive to mechanical vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency stabilised for weeks at a time. A compact, transportable vacuum system has been built, and used for laser cooling and magneto-optical trapping. We will use a mixture of quantum degenerate gases, bosonic 87Rb and fermionic 40K, in order to find the optimal conditions for precision and sensitivity of inertial measurements. Microgravity will be realised in parabolic flights lasting up to 20s in an Airbus.
Atom interferometry has hugely benefitted from advances made in cold atom physics over the past twenty years, and ultra-precise quantum sensors are now available for a wide range of applications . In particular, cold atom interferometers have shown excellent performances in the field of acceleration and rotation measurements [2,3], and are foreseen as promising candidates for navigation, geophysics, geo-prospecting and tests of fundamental physics such as the Universality of Free Fall (UFF). In order to carry out a test of the UFF with atoms as test masses, one needs to compare precisely the accelerations of two atoms with different masses as they fall in the Earth’s gravitational field. The sensitivity of atom interferometers scales like the square of the time during which the atoms are in free fall, and on ground this interrogation time is limited by the size of the experimental setup to a fraction of a second. Sending an atom interferometer in space would allow for several seconds of excellent free-fall conditions, and tests of the UFF could be carried out with precisions as low as 10-15 .
However, cold atoms experiments rely on complex laser systems, which are needed to cool down and manipulate the atoms, and these systems are usually very sensitive to temperature fluctuations and vibrations. In addition, when operating an inertial sensor, vibrations are a major issue, as they deteriorate the performances of the instrument. This is why cold atom interferometers are usually used in ground based facilities, which provide stable enough environments. In order to carry out airborne or space-borne measurements, one has to design an instrument which is both compact and stable, and such that vibrations induced by the platform will not deteriorate the sensitivity of the sensor.
We report on the operation of an atom interferometer on board a plane carrying out parabolic flights (Airbus A300 Zero-G, operated by Novespace). We have constructed a compact and stable laser setup, which is well suited for onboard applications. Our goal is to implement a dual-species Rb-K atom interferometer in order to carry out a test of the UFF in the plane. In this perspective, we are designing a dual-wavelength laser source, which will enable us to cool down and coherently manipulate the quantum states of both atoms. We have successfully tested a preliminary version of the source and obtained a double species magneto-optical trap (MOT).
High energy fiber lasers emitting around 1579nm is seen as a possible technology for the laser unit of a spaceborn CO2 DIAL system. We are developing an all fiber system with the following expected performances: pulse energy of 260μJ, pulse duration 150ns, beam quality M2 <2, pulse linewidth <60 MHz, laser stability 200 kHz. One of our main concerns has been the radiation induced attenuation mitigation. Various fiber compositions have been investigated.
Mixing process of a passive scalar in a heated turbulent jt at Reynolds numbers between 13,000 and 21,000 is studied experientaly using combined two-color Planar Laser-Induced Fluorescence (2λ-PLIF) and Particle-Image Velocimetry (PIV). The PLIF system is based on acetone fluorescence for temperature and concentration measurement. The aim of the present paper is to obtain a reliable reference data set for the validation of numerical simulation of turbulent fluxes. Experiment was carried out on a heated turbulent jet of acetone-seeded air emanating from the 10 mm-diameter nozzle exit of an electric air heater with exit temperature Ti = 500 K. The jet is seeded to approximately 3% acetone by bubbling the air stream through liquid acetone. The mean and fluctuating dynamic and thermal fields are investigated and determined. This tool will allow to determine the temperature-velocity as well as the concentration-velocity cross-correlations in order to characterize the turbulent characteristics of the flow such as the turbulent diffusivity and the turbulent Prandtl number.