Birefringence in electromagnetically induced transparency

4He 2 3S1 -> 2 3P transitions at 1083 nm were laser probed in the presence of radiation that coupled the 2 3P level with the 3 3S1 level in a ladder scheme. The metastable helium that was used was produced in a rf discharge. Significant atomic birefringence was detected, in addition to complete electromagnetically induced transparency. A simple theoretical model explains the experimental results.