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GEMINI Interferometer – discover the advantages of Fourier-Transform techniques
The gold ball used in size comparison with a one cent coin
and half a millimeter thick, suspended from a glass fibre a few thousandths of a millimeter in diameter. Gold spheres of similar size are attached to each end of the rod. ‘We move the gold sphere back and forth, creating a gravitational field that changes over time,’ explained Jeremias Pfaff, one of the researchers involved in the experiment. ‘This causes the torsion pendulum to oscillate at that particular excitation frequency.’ The movement, which is only a few millionths of a millimetre, can then be read with the help of a laser and allows conclusions to be drawn about the force.
The difficulty is keeping other influences on the motion
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as small as possible. ‘The largest non-gravitational effect in our experiment comes from seismic vibrations generated by pedestrians and tram traffic around our lab in Vienna,’ said co-author Hans Hepach: ‘We therefore obtained the best measurement data at night and during the Christmas holidays, when there was little traffic.’ Other effects such as electrostatic forces could be reduced to levels well below the gravitational force by a conductive shield between the gold masses.
This made it possible to
determine the gravitational field of an object that has roughly the mass of a ladybird for the first time. As a next step, it is planned to investigate the
Gemini is an ultra-stable, common-path (CP) interferometer which brings all the advantages of Fourier- Transform spectroscopy to the UV-VIS spectral regions. Manufactured by Nireos and available in UK and Ireland through Photonic Solutions, the GEMINI interferometer measures the spectrum of light via Fourier-Transform (FT) techniques. With all the limitations of an entrance slit removed, you no longer need to compromise on spectral resolution and
gravity of masses thousands of times lighter.
The possibility of measuring
gravitational fields of small masses and at small distances opens up new perspectives for research in gravitational physics; traces of dark matter or dark energy could be found in the behaviour of gravity – which could be responsible for the formation of our present universe. Aspelmeyer’s researchers are particularly interested in the
sensitivity. Guaranteed phase locking between the two interfering replicas ensures that the Gemini is insensitive to external perturbations and so allows it to be used in the ultraviolet-visible (UV-VIS) spectral regions, where a high degree of stability is required. As such, the accurate control of the temporal delay between the two replicas of the input light, allows unrivalled accuracy and reproducibility over an ultra-broadband spectral range of 4200nm to 4500nm, with 0.7nm spectral resolution and high throughput from a 10mm clear aperture.
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interface with quantum physics: can the mass be made small enough for quantum effects to play a role? Only time will tell. For now, the fascination with Einstein’s theory of gravity still prevails. ‘According to Einstein, the gravitational force is a consequence of the fact that masses bend spacetime in which other masses move,’ said first author Tobias Westphal. ‘So what we are actually measuring here is how a ladybug warps space-time.’ EO
April 2021 Electro Optics 29
Tobias Westphal / Arkitek Scientific
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