Guillaume Michel
Associate professor at Sorbonne Université
Associate professor at Sorbonne Université
- Several measurement methods can be used to visualize flows in transparent media and rely on the dependence of the refractive index on the local density. The most famous device, that can be explained by ray optics, is the schlieren imaging system. With only a few modifications, it can be turned into an interferometer, that now relies on physical optics. Some of the typical results achieved thanks to the latter are shown in the video below: the flows associated with a candle, a human breathing, a hair dryer and a mass cooled with liquid nitrogen. There is of course room for improvement.
- Water waves on earth result from two restoring forces in competition: gravity and capillarity. Operating in microgravity allows to neglect gravity. This conditions provide a simplified framework to investigate how pure capillary waves interact with one another. The following setup, with minor modifications, was installed on the international space station and operated by four astronauts (Thomas Pesquet, Paolo Nespoli, Norishige Kanai and Alexander Gerst). It consists of a spherical container partially filled with water and undergoing back and forth oscillations. In weighlessness, the water wets the internal surface of the sphere, forming a large air bubble in the center surrounded by a water shell on which capillary waves propagate. This video captures the transient wetting dynamics governed by strong sloshing motions and was taken during a parabolic test flight: water transitions from hypergravity to microgravity and the other way around, respectively at around 20s and 47s in the video. See M. Berhanu et al., EPL 128, 34001 (2019) for more details.
- When a material experiences mechanical deformations, its microscopic structure becomes strongly anisotropic and its optical properties evolve accordingly. For transparent samples, this feature can be used to visualize and measure the stress distribution. I have designed a new practical work on this topic for undergraduate students, here is what can be easily achieved.
