Experimental evidence of a pump-wavefront-induced Stern–Gerlach-like splitting in optical parametric generators

Quantum mechanical Stern-Gerlach (SG)-like effects are unusual to explore in the domain of optics due to the absence of any interaction of photons or optical waves with the conventional magnetic field. A few recent investigations point toward the possibility of observing an SG-like effect in nonlinear optics via wedge-shaped poling in a long lithium niobate (LN) crystal to generate a spatially varying analogous magnetic field (B→A). This leads to two different propagation directions for the mutually orthogonal states formed by superposition of signal and idler modes (states) with opposite phases. In this work, we present theoretical formalism to show an equivalent SG-like splitting in a frequency downconversion process and experimentally validate the assertion by producing a suitable transverse gradient in B→A through an in-homogeneous pump wavefront. The experimental results show SG-like splitting in an optical parametric generation (OPG) process using a widely used periodically poled LN (PPLN) crystal and a pump laser exhibiting a suitable spatial beam profile. The experimentally measured deviation angle for the mutual beam closely matches with the prediction from theoretical formalism using a Gaussian pump wavefront.