Based on the Nature article abstract images it appears they were able to image the cloud using the VLT telescope. I got confused about L'-band for a second. Thought they were talking about L-band.

Feel free to correct me if someone has read the article.

[1] http://www.nature.com/nature/journal/vaop/ncurrent/full/natu...

[2] http://www.eso.org/public/teles-instr/vlt.html

[edited for mistake]