Searching for Axion-Photon Coupling with Baselines of kpc to Gpc

Axion couplings to photons could induce photon-axion conversion in the presence of magnetic fields in the Universe. In the first half of talk, I will show that this conversion impacts various cosmic distance measurements, such as luminosity distances to type Ia supernovae and angular distances to galaxy clusters. I will consider different combinations of the most up-to-date distance measurements to constrain the axion-photon coupling. In the second half, I will briefly discuss the axion stimulated decay, a novel approach to constrain axion-photon coupling by observing the echo signals in directions *opposite* to galactic supernova remnants (SNR) in the radio band. I will demonstrate that the strength of the "echo" signal from axion stimulated decay depends on the history of photon source. Even though SNRs are dim today, they could lead to the strongest bound of photon-axion coupling for axions around 10^{-6} eV.