The first scientist to provide experimental evidence that light is a wave was Thomas Young, an English polymath and physician. Young conducted a famous experiment known as Young's double-slit experiment in 1801, which demonstrated the wave nature of light.
In his experiment, Young shone a beam of light through a barrier that had two narrow slits. The light passing through the slits created an interference pattern on a screen placed behind the barrier. This pattern consisted of alternating bright and dark fringes, indicating that light waves were interfering with each other, much like water waves or sound waves.
Young's double-slit experiment provided strong evidence that light behaves as a wave and exhibited characteristics such as diffraction and interference. His work significantly contributed to the understanding of light as a wave phenomenon, laying the foundation for the wave theory of light in the field of optics.