Experimental measurements of the Paschen–Back effect in helium triplet transitions

Experimental confirmation of the theoretical calculations of the Zeeman and Paschen–Back effects in the prominent 2 3S – 2 3P He I 1083 nm near-infrared (NIR) transition by means of high-resolution spectroscopy is reported. A novel approach using a small-pixel-size fluorescence camera delivers required spectral resolution. In particular, it allows to quantify with good precision the spectral shift of the weak λ0 = 1082.9 nm line from the zero magnetic field position. Measurements of the strong visible (VIS) He I 587 and 706 nm triplet line shapes are reported for B = 0–1.0 T interval, indicating nonlinear wave function mixing as well.