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:

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.


  • R.F. Offer, D. Stulga, E. Riis, S. Franke-Arnold and A.S. Arnold, Spiral bandwidth of four-wave mixing in Rb vapourComms. Phys. 1, 84 (2018).
  • R.F. Offer, J.W.C. Conway, E. Riis, S. Franke-Arnold and A.S. Arnold, Cavity-enhanced frequency up-conversion in rubidium vapor, Opt. Lett. 41, 2177-2180 (2016).
  • Clark, TW ; Offer, RF; Franke-Arnold, S; Arnold, AS; Radwell, N, Comparison of beam generation techniques using a phase only spatial light modulator, Opt. Express 24 6249-6264 (2016).
  • G. Walker, A.S. Arnold and S. Franke-Arnold, Trans-spectral orbital angular momentum transfer via four-wave mixing in Rb vaporPhys. Rev. Lett. 108, 243601 (2012).
  • Arnold, AS, Extending dark optical trapping geometriesOpt. Lett. 37, 2505 (2012).
  • A. Vernier, S. Franke-Arnold, E. Riis and A.S. Arnold, Enhanced frequency up-conversion in Rb vaporOpt. Express 18, 17020 (2010).
  • Franke-Arnold, S; Leach, J; Padgett, MJ; Lembessis, VE; Ellinas, D; Wright, AJ; Girkin, JM; Ohberg, P; Arnold, AS, Optical ferris wheel for ultracold atomsOpt. Express 15, 8619 (2007).