Polarization signatures of mixed scalar - pseudoscalar ALP - photon couplings in intense laser pulses
We investigate photon-to-axion-like-particle (ALP) conversion in a finite, linearly polarized laser pulse for a single ALP field with simultaneous scalar-type and pseudoscalar-type couplings to photons. Varying the collision angle between the strong pulse and the probe provides a continuous kinematic scan of the resonant ALP mass. For fixed kinematics in this setting, the scalar-type and pseudoscalar-type ALP conversion amplitudes interfere coherently, making both the photon-to-ALP conversion probability and the polarization rotation depend on the difference between the probe polarization angle $α$ and the coupling angle $θ_g$. Conversion is maximal at $|α-θ_g|=90^\circ$, where the polarization rotation vanishes, while the rotation magnitude peaks at $α-θ_g=45^\circ$ modulo $90^\circ$, where conversion is half-maximal. These complementary polarization-angle dependences provide polarization-resolved signatures of mixed scalar--pseudoscalar photon couplings.