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.