Abstract
The orbital angular momentum (OAM) of beams provides a new dimension, and have already found lots of applications in various domains. Among such applications, the precisely and quantitatively diagnostic of intensity distributions among different OAM modes, namely the OAM spectrum of a beam, is of great significance. In this paper we propose and experimentally validate a simple interferential method to achieve this goal. By analyzing the interference pattern formed by the beam and a reference field, the OAM spectrum can be obtained instantaneously. Furthermore, the proposed method is also available for more complex light fields, for instance, the multi-ring optical vortices. In the proof-of-concept experiment, the OAM spectra of both single-mode and N-fold multiplexed OAM modes with various intensity distributions are well detected. Our work offers a new way to precisely measure the OAM spectra of beams and will advance the development of many applications ranging from classical to quantum physics as the OAM based large-capacity data transmissions, rotation detection, quantum manipulation and so on.
Highlights
Since Allen et al proved in 1992 that a light beam whose complex amplitude comprises the helical term exp(ilφ) with l the topological charge and φ the azimuthal angle carries a definite amount of orbital angular momentum (OAM) [1], studies on beam’s OAM came into researcher’s sight and got great development
OAM spectrum analyzing for single modes Firstly we employ the proposed OAM spectrum analyzer to measure single-mode OAM beams to see the analyzing performance
In summary, we have proposed a universal OAM spectrum analyzer for beams, where a reference Gaussian beam is introduced and combined coaxially with the initial beam, and the OAM spectrum can be well calculated from the intensity patterns
Summary
Since Allen et al proved in 1992 that a light beam whose complex amplitude comprises the helical term exp(ilφ) with l the topological charge and φ the azimuthal angle carries a definite amount of orbital angular momentum (OAM) [1], studies on beam’s OAM came into researcher’s sight and got great development. Previous studies have already illustrated that in such beams the OAM value carried by each photon equals to lħ, where ħ is Planck constant divided by 2π [1, 2]. The topological charge is the eigen value and determines the OAM value each photon carry. OAM beams known as vortex beams [3] or twist beams [4]. These unique features of OAM beams make it possible to find wide applications in lots of domains ranging from classical to quantum physics, for instance, the large-capacity data (2020) 1:19 transmission [5,6,7,8,9], rotation probing [10,11,12,13], optical tweezers and micromanipulation [14, 15], imaging [16], quantum information [17, 18], gravitational wave detection [19, 20], astronomy [21] and so on
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