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
  • spectral narrowing and further enhancement of efficiency via the use of a ring cavity around the Rb cell

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. Trans-spectral OAM transfer. If the 780nm and 776nm beams carry an orbital angular momentum of l, the 420nm beam has OAM 2l. Here OAM superpositions in the near infrared are transferred to 420nm.


  • 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).