The fringe model can directly explain the principle of dual beam differential Doppler effect. Superimposed state vortex light is a petal-like interference fringe superposed by positive and negative topological charge vortex beams. Based on this, the idea of fringe model is applied to the principle of rotational speed measurement based on the rotation Doppler. The rotation Doppler frequency shift based on the model was derived by means of spatial geometric transformation. According to the relative location between the optical axis of vortex and the object rotation axis, three typical incident conditions which are coincident, offset and tilt are considered. The results show that the frequency shift based on the fringe model is consistent with that of the traditional rotation Doppler model, which proves that the model is suitable for the interpretation of the principle of rotation Doppler velocity measurement. This study provides a more intuitive and concise theoretical explanation for the rotational Doppler effect, which has certain guiding significance.
Optical vortex is a kind of unique structure light with a helical phase distribution and contains orbital angular momentum. It has been found a myriad of important applications of optical vortex, such as micromanipulation, remote sensing and communication. In recent years, there are many researches on the particle manipulation based on the orbital angular momentum of optical vortex. Especially, there is a new kind of optical vortex which is so-called “perfect” vortex whose ring radius is independent of its topological charge has an outstanding performance on the micromanipulation. However, the exist experiments can only realize manipulation of particle and the rotation speed is difficult to obtain. In this paper, we proposed a new scheme which can manipulate the particle and simultaneously detect its rotation speed. We employ the superposition perfect vortex as the probe beam. It is worth to note that the topological charge of the perfect vortex we used has an opposite sign and different magnitude. Therefore, the probe beam possesses remaining orbital angular momentum and can generate the rotational Doppler effect. The rotational Doppler effect is the basics of rotation speed detection. A corresponding experiment has been conducted to verify our method. The results have confirmed the existence of orbital angular momentum of superposition optical vortex with different topological charge. Our scheme can realize manipulation and detection the rotation speed of the particle simultaneously. It is an important supplement on the micromanipulation and maybe useful in the optical gyroscope technique.
The vortex light containing orbital angular momentum (OAM) has important application prospects in precision measurement, micro particle manipulation and basic physics. Because the Poynting vector of the vortex wave is not in line with the direction of the optical axis, more information is contained in the echo than the ordinary electromagnetic wave, so it has a unique advantage in the detection of unknown object. The wave propagation characteristics of the vortex beam are modeled and analyzed. Based on the Michelson interference principle, a new type of vortex light interference scheme is designed. The measurement scheme of the wavelength of the vortex light is proposed and the experimental verification is carried out. On this basis, a new method for detecting non-cooperative targets in space is proposed and analyzed theoretically. It provides a new way for measuring angular velocity of objects by vortex optics, and lays a good foundation for remote sensing of non-cooperative targets in actual demand in the future.
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