Giant polarization drag in a gas of molecular super-rotors

Abstract

Experiments on light dragging in a moving medium laid the cornerstones of modern physics more than a century ago, and they still are in the focus of current research. When linearly polarized light is transmitted through a rotating dielectric, the polarization plane is slightly rotated -a phenomenon first studied by Fermi in 1923. For typical non-resonant dielectric materials, the measured polarization drag angle does not surpass several microradians. Here we show that this effect may be dramatically enhanced if the light is sent to a gas of fast unidirectionally spinning molecular superrotors. Several femtosecond-laser labs have already succeeded in optically creating such a medium. We show that the specific rotation power of the superrotor medium exceeds the values previously observed in mechanically rotated bulk optical specimens by many orders of magnitude. This nonreciprocal opto-mechanical phenomenon may open new avenues for ultra-fast control of the polarization state of light.Main text: Light propagating in a moving medium can be 'dragged' by it and change the speed depending on the medium motion. This was first discussed by Fresnel in 1818 when considering a hypothetical 'aether drag' [1], and studied experimentally by Fizeau [2] in a real moving dielectric medium-water flowing in the arms of an optical interferometer. In 1885 Thomson considered an electromagnetic wave traveling in a rotating aether [3], and argued that the light should experience a transverse drag leading to the rotation of the field polarization vector. While the Michelson-Morley experiment [4] essentially ruled out the notion of 'luminiferous aether', the problem of polarization drag in a real rotating matter was examined by Fermi [5], who considered it as a generalization of the Fizeau experiment. The phenomenon was then studied in depth theoretically [6,7,8], and was first observed experimentally by Jones [9] using a rotating glass rod. The observed polarization rotation angle (which is proportional to the angular velocity of the glass rotation, and to the time it takes the light to traverse the specimen) was very smallseveral microradians. Jones' experiment approached the mechanical and material strength limits, and for more than 30 years no other research managed to exceed or reproduce his result. A remarkable advance was introduced in 2011 when the rotary polarization drag was enhanced by about four orders of magnitude by using near-resonant slow-light in a rotating solid ruby rod [10]. Recently it was shown that the rotary polarization drag takes place on astronomical scale in the magnetosphere of rotating pulsars, offering a unique means to determine the rotation direction of pulsars [11]. The effect is especially important since it is nonreciprocal, i. e., creates asymmetric wave transmission between two locations.Here we propose an alternative system for creating rotational polarization drag at unprecedentedly 1 high specific rotation level -four orders of magnitude higher than in the above record slow-light experiment [10], a...

Enhanced tuneable rotatory power in a rotating plasma

“…Since δ m ∝ ω c , the specific rotatory power can also be controlled online through the rotation frequency Ω and the plasma density n e . Quantitatively, δ m ∼ 1 rad m −1 for the baseline parameters (n e , B 0 , Ω ), which is again comparable to that obtained by exploiting slow light conditions in a ruby window [38], or the extremely large rotation of molecular super-rotors [39]. Also, while such specific rotatory power values are well below those obtained at THz frequency for instance on epitaxial HgTe thin films (∼ 10 6 rad m −1 ) [43] or in graphene (∼ 10 8 rad m −1 ) [28], magnetized plasma channels' length can be much longer than the thickness d of these media.…”

“…For the baseline parameters (n e , B 0 , Ω ) (see Table I), this yields γ ≥ 10 4 which is comparable to the enhancement obtained by exploiting resonant conditions in a ruby window [38], or that of a gas of molecular super-rotors [39] but for a mechanical rotation frequency 10 orders of magnitude smaller. Note that this circular birefringence enhancement in a rotating plasma near the cutoff frequency can be interpreted, similarly to the enhancement found using slow light in a ruby window [38], as the effect of a very large effective group index.…”

Faraday–Fresnel rotation and splitting of orbital angular momentum carrying waves in a rotating plasma

“…At high frequency the electrons’ inertia response dominates the dispersion relation and (2.1) can be expanded to give the phase difference between the and modes accumulated when propagating one wavelength along : The phase difference derived in (2.2) is the classical formula describing the high-frequency Faraday SAM rotation in a magnetised plasma at rest. A very similar result, though not with the same frequency scaling, can be obtained by considering the phase velocity difference between right- and left-circularly polarised wave as a result of the medium's rotation (Jones 1976; Player 1976; Götte et al 2007; Gueroult et al 2020; Steinitz & Averbukh 2020; Milner et al 2021).…”

Rotation of polarization of light propagating through a gas of molecular super-rotors

“…We can express the angle of polarization rotation using Eq. ( 6) in terms of polarizabilities in Eq (12) and their derivatives (with respect to the driving frequency ω)…”

“…Another major hurdle is the rapid rotation of a gaseous medium required to induce a measurable polarization drag. However, recently we proposed a workaround [12], suggesting that instead of mechanically rotating a bulky dielectric object as a whole, one could excite a fast unidirectional rotation of individual microscopic particles. Current laser techniques (for recent reviews, see, e.g., [13][14][15][16]) including cross-polarized pulse pairs [17][18][19], chiral pulse trains [19], polarization-shaped pulses [20], and, especially, optical centrifuges [21][22][23][24][25][26], can bring molecules in the gas phase to very fast spinning.…”