Which physicist's work led to the first operational laser device?

The correct answer is Theodore Maiman, as he is recognized for developing the first operational laser device. In 1960, Maiman successfully demonstrated the first working laser, which utilized a ruby crystal as the medium for light amplification. His invention was significant as it proved the principles of stimulated emission proposed by Albert Einstein earlier in the 20th century, but it was Maiman who took the theoretical concepts and built the first functional device, marking a pivotal moment in the field of optics and photonics.

While Albert Einstein's earlier work laid the foundational principles for laser technology through his explanation of stimulated emission, he did not create the first laser. Nikola Tesla's contributions to electricity and electromagnetism did not directly pertain to the development of laser technology. Gordon Gould, on the other hand, made important advancements and played a key role in the patenting process of laser technology, but it was Maiman's prototype that first realized the laser's capabilities in practice. This historic achievement established Maiman as a central figure in the inception of laser technology.