Sound emission from the gas of molecular superrotors

Abstract

We use an optical centrifuge to deposit a controllable amount of rotational energy into dense molecular ensembles. Subsequent rotation-translation energy transfer, mediated by thermal collisions, results in the localized heating of the gas and generates strong sound wave, clearly audible to the unaided ear. For the first time, the amplitude of the sound signal is analyzed as a function of the experimentally measured rotational energy. The proportionality between the two experimental observables confirms that rotational excitation is the main source of the detected sound wave. As virtually all molecules, including the main constituents of the atmosphere, are amenable to laser spinning by the centrifuge, we anticipate this work to stimulate further development in the area of photo-acoustic control and spectroscopy.

Dynamics of molecular superrotors in an external magnetic field

“…Gyroscopic precession along the direction of the applied magnetic field has been suggested for non-magnetic molecules in dispersionless "cogwheel" states [3,4]. Spin-rotational coupling has been recently utilized for converting unidirectional molecular rotation into axial alignment, manifested through magneto-rotational optical birefringence under ambient conditions [5,6].…”

“…The technique proved capable of producing synchronously rotating molecules with narrow rotational state distribution in a wide variety of species up to extremely high angular frequencies [5,23]. However, the spatial orientation of the induced angular momentum is often defined by the propagation direction of the excitation laser beam, and is therefore not easy to manipulate.…”

“…Gyroscopic precession along the direction of the applied magnetic field has been suggested for non-magnetic molecules in dispersionless "cogwheel" states [3,4]. Spin-rotational coupling has been recently utilized for converting unidirectional molecular rotation into axial alignment, manifested through magneto-rotational optical birefringence under ambient conditions [5,6].Recent progress in creating and detecting unidirectional rotation of molecules [7][8][9][10][11]18] revived the interest in controlling molecular rotation with external magnetic fields. Magnetic effects could further broaden the controllability provided by tunable rotational excitation, including control of molecular collisions [12,13] and scattering of molecules at gas-solid interfaces [14], molecular trajectories [15] and formation of gas vortices [16], optical [5, 17] and acoustic [19,20] properties of a gas of rotating molecules.…”

“…Spin-rotational coupling has been recently utilized for converting unidirectional molecular rotation into axial alignment, manifested through magneto-rotational optical birefringence under ambient conditions [5,6].…”

“…Magnetic effects could further broaden the controllability provided by tunable rotational excitation, including control of molecular collisions [12,13] and scattering of molecules at gas-solid interfaces [14], molecular trajectories [15] and formation of gas vortices [16], optical [5, 17] and acoustic [19,20] properties of a gas of rotating molecules.…”