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 $\alpha$ and the coupling angle ${\theta }_g$. Conversion is maximal at $\mathrm{\mid }\alpha -{\theta }_g\mathrm{\mid }={90}^{\circ }$, where the polarization rotation vanishes, while the rotation magnitude peaks at $\alpha -{\theta }_g={45}^{\circ }$ modulo ${90}^{\circ }$, where conversion is half-maximal. These complementary polarization-angle dependences provide polarization-resolved signatures of mixed scalar–pseudoscalar photon couplings.