Interference patterns for simple lens models in wave-optics regime

Abstract

This work studies interference patterns created by simple lens models (point mass, Chang–Refsdal, and binary lens) in the wave optics regime, primarily in the context of lensing of gravitational waves (GWs) in the LIGO band at frequencies around 100 Hz. We study how the interference patterns behave close to the caustic curves, which mark the high-magnification regions in conventional geometric optics. In addition, we also look at the formation of highly de-amplified regions in the amplification maps close to caustics and how they differ under wave and geometric optics. We see that, except for close to caustic regions, the geometric optics track the oscillations of the amplification factor in frequency very well, although the amplitude of these oscillations can differ considerably. Chang–Refsdal and binary lenses with masses \({\sim }\)100–200 \(M_\odot \) can introduce significant de-amplification at frequencies \({\sim }\)100 Hz when the source is close to caustics, which may help us distinguish such lenses from the point mass lens.