a, IPL versus B for NV1 at specified magnetic-field angles θ. b, Zoom of data in a (points) with fits (lines) to model described in the text. Data for θ=0∘ are taken with smaller field steps and fit with an angle of 0.2∘ to account for residual spin mixing (see the text). c, IPL versus B for NV4 (points) and fits (lines) at specified field angles. d, Normalized amplitudes A (points) of LAC and 500-G peaks versus θ with fits (lines). Laser power is 1 mW for NV1 and 2.9 mW for NV4.