Einstein Beams: Recreating the Wave Patterns of Gravitational Lensing

We recreate the optical beams of gravitational lensing in the laboratory. We use a spatial light modulator (SLM) to deflect the components of the wavefront of a monochromatic laser beam into gravitationally lensed trajectories. By suitably programing the SLM we were able to recreate all the observations of gravitational lensing plus new features that have not been observed. Our recreations include two types of observations. One type are the ray-geometric features, such as Einstein rings and arcs. The other type are the wave features, where wave interference produces optical patterns following Bessel-function shapes when the lensing object is symmetric, and more complex astroid patterns exhibiting caustics modulated by interferences when the lensing object is asymmetric (elliptical or binary). The remarkable feature of Einstein beams is that they are an intermediate case of non-diffracting Bessel beams and diffracting Gaussian beams, and thus have a pattern that is preserved upon propagation with a slow expansion. Thus, besides their intrinsic interest for investigating lensing, they may be used in optical applications. With our laboratory technique we have investigated other features that have not been seen clearly or widely in astrophysical observations, such as lensed light carrying angular momentum, self-healing and the wavelength dependence of patterns. The technique can also be used to model lensing situations that are difficult to simulate analytically or computationally.