The experimental determination of the wave-particle duality of photons can be attributed to a series of historical experiments in the early 20th century. Here are a few key experiments that contributed to our understanding of the duality of photons:
The Photoelectric Effect (1887-1905): The photoelectric effect experiments conducted by Heinrich Hertz, Philipp Lenard, and later Albert Einstein provided crucial evidence for the particle-like behavior of light. They observed that when light shines on a metal surface, electrons are ejected from the surface. The observed effects, such as the dependence of the emitted electron energy on the frequency of light rather than its intensity, could not be explained solely by a wave model of light. Einstein's explanation, which earned him the Nobel Prize in 1921, proposed that light is composed of discrete energy packets or photons, with each photon carrying a specific quantum of energy.
The Double-Slit Experiment (1801, 1961): Thomas Young's double-slit experiment, initially performed with light waves, demonstrated the interference pattern produced when light passes through two closely spaced slits. In 1961, a variation of this experiment was performed using a low-intensity beam of single photons. The experiment revealed that individual photons, when sent through the double slits one at a time, could still produce an interference pattern on the screen behind the slits. This showed that photons exhibit wave-like behavior in terms of interference, even when detected one by one.
Compton Scattering (1923): Arthur H. Compton's experiments involved shining X-rays onto a target material and observing the scattered X-rays. He found that the scattered X-rays experienced a change in wavelength and angle of scattering. This phenomenon could not be explained purely by a wave model of light but was consistent with the particle nature of photons. Compton's experiments provided further evidence for the existence of discrete, particle-like interactions between photons and matter.
These experiments, along with subsequent research and theoretical developments, collectively established the wave-particle duality of photons. They demonstrated that photons exhibit both particle-like behavior (as discrete packets of energy) and wave-like behavior (interference and diffraction), depending on how they are observed or measured. This duality is now an integral part of quantum mechanics and our understanding of the nature of light.