[Seminar] Dr Akulshin 'Addition, Subtraction and Cancellation of Optical Topological Charges in Two-Photon Excited Rb Vapour'

Speaker:
Associate Professor Alexander M. Akulshin
Centre for Quantum and Atom Optical Science, Swinburne University of Technology, Australia

Seminar Title:
Addition, Subtraction and Cancellation of Optical Topological Charges in Two-Photon Excited Rb Vapour

Abstract:
Structured light is a rapidly developing subfield of optics that promises numerous intriguing applications, including optical communication, particle manipulation, and quantum information processing. The study of resonant vortex light interaction with atomic media has attracted considerable attention [1-4]. This work is motivated by the possibility to produce topologically correlated vortex fields from different spectral regions, which is of interest for future quantum information networks.

We report on experimental investigations of transfer of optical topological charges from applied laser fields at 780 and 776 nm which two-photon excite Rb atoms to the 5D5/2 level to the fields generated by parametric FWM. The two-photon induced population inversion on the 5D5/2→6P3/2 transition results in the appearance of directional radiation at 5.23 µm due to amplified spontaneous emission (ASE) in a pencil-shaped excitation region. Parametric wave mixing of this internally generated field with the applied laser light produces the temporally and spatially coherent blue light in directions along which the phase-matching relations are satisfied.  

Investigating topological charge transfer we find that

- In a wide range (0.05−2)×1012 cm−3 of Rb number densities and under more than 50-fold laser intensity variations the blue light accumulates the total topological charge of the laser light.

- The applied vortex laser light can produce OAM-free CBL if the applied vortex beams at 780 and 776 nm carry equal in magnitude but opposite in sign topological charges.

- The transfer of total OAM from laser light to CBL occurs even if the applied beams are not perfectly collinear.

We also show that the OAM transfer to new optical fields can be used for identifying the major nonlinear processes responsible for their generation.

[1] G. Walker, A.S. Arnold, S. Franke-Arnold, Phys. Rev. Lett. 108, 243601 (2012).
[2] A. M. Akulshin, R. J. McLean, E. E. Mikhailov, and I. Novikova, Opt. Lett. 40, 1109 (2015).
[3] R. A. de Oliveira, G. C. Borba, W. S. Martins, S. Barreiro, D. Felinto, and J. W. R. Tabosa, Opt. Lett. 40, 4939 (2015).
[4] A.M. Akulshin, I. Novikova, E. E. Mikhailov, S.A. Suslov, and R. J. McLean, Opt. Lett. 41, 1146 (2016).