Nature Communications 8:745 doi:10.1038/s41467-017-00764-5; Article published online: 29 Sep 2017

The published version of this Article contained an error in the second sentence of the fourth paragraph of the subheaded section “Ellipticity and helicity of the emitted harmonics”. The final exponent in this sentence should read: inπ/2. This has now been corrected in the PDF and HTML versions of the Article.