Enhanced blue light generation in Rb vapour – EQOP Group @ Strathclyde Physics

In this Strathclyde/Glasgow collaboration we have observed highly efficient generation of 420 nm laser light via up-conversion of near-infrared lasers in a hot rubidium vapor cell, with single-pass conversion efficiency of 260%/W, significantly higher than in previous experiments. Favorable scaling of our current 1mW blue beam power with additional pump power has been shown. We have investigated:

the power-, polarisation-, frequency-, temperature- efficiency, of the four-wave mixing process
trans-spectral orbital angular momentum (OAM) transfer, utilising optimised spatial light-modulator (SLM) patterns
the best holograms on spatial light modulators (SLMs) for making OAM modes
spectral narrowing and further enhancement of efficiency via the use of a ring cavity around the Rb cell
the quantitative OAM distribution of the generated light and inferred spiral bandwidth


Relevant Rb energy levels for the four-wave mixing process.	(Top) 1mW of 420nm light from ~20+20mW of focused 780nm and 776nm light. (Bottom) 420nm beam power with (blue, 1MHz linewidth) and without (red) a ring cavity.	Experimental image of a 420nm laser beam carrying trans-spectral OAM transferred from the near-infrared pump beams. Quantitative information on the OAM is found by using Fourier methods on the interferogram formed when the beam is overlapped with its mirror image.

Funding: Leverhulme Trust RPG-2013-386.

Publications

R.F. Offer, A. Daffurn, E. Riis, P.F. Griffin, A.S. Arnold & S. Franke-Arnold, Gouy phase-matched angular and radial mode conversion in four-wave mixing, Phys. Rev. A 103, L021502 (2021).
R.F. Offer, D. Stulga, E. Riis, S. Franke-Arnold & A.S. Arnold, Spiral bandwidth of four-wave mixing in Rb vapour, Comms. Phys. 1, 84 (2018).
R.F. Offer, J.W.C. Conway, E. Riis, S. Franke-Arnold & A.S. Arnold, Cavity-enhanced frequency up-conversion in rubidium vapor, Opt. Lett. 41, 2177 (2016).
T.W. Clark, R.F. Offer, S. Franke-Arnold, A.S. Arnold & N. Radwell, Comparison of beam generation techniques using a phase only spatial light modulator, Opt. Express 24, 6249 (2016).
G. Walker, A.S. Arnold & S. Franke-Arnold, Trans-spectral orbital angular momentum transfer via four-wave mixing in Rb vapor, Phys. Rev. Lett. 108, 243601 (2012).
A.S. Arnold, Extending dark optical trapping geometries, Opt. Lett. 37, 2505 (2012).
A. Vernier, S. Franke-Arnold, E. Riis & A.S. Arnold, Enhanced frequency up-conversion in Rb vapor, Opt. Express 18, 17020 (2010).
S. Franke-Arnold, J. Leach, M.J. Padgett, V.E. Lembessis, D. Ellinas, A.J. Wright, J.M. Girkin, P. Ohberg & A.S. Arnold, Optical ferris wheel for ultracold atoms, Opt. Express 15, 8619 (2007).