In 2013, Padgett’s group recognized that the well-known Doppler shift and Doppler velocimetry had an angular equivalent, and other works about measurement of transverse velocity based on rotational Doppler Effect were also presented. In 2014, the physical mechanism of rotational Doppler Effect was theoretically studied. But this work was the case where the observer spun relative to the beam axis. A more general case is that a fixed input light illuminates a spinning object and the scattered light has a frequency shift. The mechanism of the frequency shift is still not very thorough. For example, it is still not clear how the surface of object influences the frequency shift content and what is the relationship between the incident light, scattered light and the surface.
Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, and Dr. Hailong Zhou, and their colleborator Prof. Pei Zhang from Xi’an Jiaotong University have put forward a theoretical model to sufficiently investigate the optical rotational Doppler Effect based on modal expansion method. We find that the frequency shift content is only determined by the surface of spinning object and the reduced Doppler shift is linear to the difference of mode index between input and output orbital angular momentum (OAM) light, and linear to the rotating speed of spinning object as well. An experiment is carried out to verify the theoretical model. We explicitly suggest that the spatial spiral phase distribution of spinning object determines the frequency content. The theoretical model makes us better understand the physical processes of rotational Doppler Effect, and thus has many related application fields, such as detection of rotating bodies, imaging of surface and measurement of OAM light.
This work has been on-line published in Optics Express on 14 July 2014 . Relative work was partially supported by the Program for New Century Excellent Talents in Ministry of Education of China (Grant No. NCET-11-0168), a Foundation for the Author of National Excellent Doctoral Dissertation of China (Grant No. 201139), the National Natural Science Foundation of China (Grant No. 11174096, 11374008 and 61475052), Foundation for Innovative Research Groups of the Natural Science Foundation of Hubei Province (Grant No. 2014CFA004). Full text can be viewed by
1 Zhou, H., Fu, D., Dong, J., Zhang, P. & Zhang, X. Theoretical analysis and experimental verification on optical rotational Doppler effect. Opt. Express 24 (2016).
Fig. 1. Principle of Rotational Doppler Effect