Measuring orbital angular momentum of light with a torsion pendulum

Abstract

We report experiments aimed at measuring the orbital angular momentum of light by means of a torsion pendulum, in the spirit of the classical spin angular momentum experiment by Beth (1936) but using present-day technology. Although our set-up has adequate sensitivity and resolution to measure orbital angular momentum of light, the systematic errors that are caused by the inherent asymmetry in the conversion of orbital angular moment remain a problem.

Direct Mechanical Detection and Measurement of Wave-Matter Orbital Angular Momentum Transfer by Nondissipative Vortex Mode Conversion

“…To our knowledge, only two experimental attempts have been reported so far. In 2005, Beijersbergen and Woerdman implemented the original optical proposal by Allen et al, however concluding negatively [22]. Ten years later, Wunenburger et al suggested the use of acoustic chiral scattering as a nondissipative process [23].…”

Torsional Mechanical Oscillator Driven by the Orbital Angular Momentum of Sound

“…The conservation of angular momentum implies that the torsional pendulum acquires angular momentum, also directed along the z axis. Harmonic modulation of the pressure field magnitude is therefore expected to drive the torsional pendulum to resonance when the forcing frequency matches that of the mechanical oscillator, whose natural frequency 2331-7019/20/13(6)/064069 (8) 064069-1 © 2020 American Physical Society is F 0 = (1/2π) √ K/J , where K > 0 is the torsion constant of the wire and J is the moment of inertia of the suspended part of the pendulum along the z axis.…”

“…It is also a torsional pendulum that was used to detect and measure mechanically the spin angular momentum of electromagnetic waves in the optical domain [4,5] in the 1930s and years later in the radio domain [6]. Of note, its orbital counterpart was implemented only a few years ago in the radio domain [7] and in the optical domain [8,9]. The mechanical manifestation of the orbital angular momentum of sound waves has also been revealed using a torsional pendulum [10,11].…”

Cholesteric polymers and the orbital angular momentum of light

“…The first investigations along this line dealt with the mechanical angular momentum transfer of OAM light to astigmatic objects. [3][4][5][6] This has led to important developments in optical tweezers, 3 particularly in a biomedical context, 7 and is well understood. The situation is quite different when we deal with the transfer of OAM to free atoms or molecules; this topic has been addressed in a number of theoretical papers 8-16 and one experimental paper.…”