1678: Christiaan Huygens hypothesises light as a wave phenomenon.
1704: Isaac Newton publishes 'Opticks' - he believed light was a particle.
1801: Thomas Young's double slit interference experiment confirms light as a wave phenomenon.
1816: Augustine-Jean Fresnel proposes Huygens-Fresnel wavelets to describe interference & diffraction.
1860: James Maxwell identifies light as an electromagnetic (e/m) wave.
Rayleigh, Kirchhoff, Sommerfeld develop scalar theory of diffraction of e/m waves.