Extended Data Fig. 1: Calculated transverse optical torque density inside the unperturbed anisotropic slab.

Calculated transverse spatial profiles of the normalized optical torque density Cartesian components Γ_x and Γ_y for an incident Gaussian field having a linear polarization state oriented along the x axis and propagating along the z axis, where 0≤ξ≤L refers to the propagation distance along the optical axis of the crystal from its input facet that defines ξ = 0. Two values of the internal Gaussian beam divergence angle are considered: θ₀ = 1^∘ (a) and θ₀ = 10^∘ (b). Each box is centered on (x, y) = (0, 0) and covers an area δL × δL where δ = 2w(z)/L. Each plot is normalized to the maximal value of the plot at ξ = L on the same row and \(\max ({\varGamma }_{x}{| }_{\xi = L})=1.2\times 1{0}^{-3}\max ({\varGamma }_{y}{| }_{\xi = L})\) for θ₀ = 1^∘ whereas \(\max ({\varGamma }_{x}{| }_{\xi = L})=0.60\max ({\varGamma }_{y}{| }_{\xi = L})\) for θ₀ = 10^∘. Parameters: δ = 1.5, L = 57μm, n_∥ = 1.756 and n_⊥ = 1.528. See Methods for details.