Explore the dual nature of light as both a wave and a particle, understanding the photoelectric effect, photon theory, and wave-particle duality.
The Quantum Nature of Light
Key concepts, historical milestones, experimental evidence, and theoretical framework
| Year | Event | Significance |
|---|---|---|
| 1801 | Thomas Young’s double‑slit experiment | Demonstrated interference → wave nature of light. |
| 1900 | Max Planck – Black‑body radiation | Introduced energy quantization (E = h\nu). |
| 1905 | Albert Einstein – Photoelectric effect | Proposed light quanta (photons) with (E = h\nu). |
| 1913 | Niels Bohr – Atomic model | Used quantized photon emission/absorption to explain spectra. |
| 1925–1927 | Development of quantum mechanics (Heisenberg, Schrödinger, Dirac) | Formalized photon as a field quantum. |
| 1932 | Arthur Compton – X‑ray scattering | Confirmed photon momentum (p = h/\lambda). |
| 1947 | First laser (Maiman) | Practical source of coherent photons. |
| 1960s–70s | Quantum optics experiments (Han‑Han, Bell tests) | Showed non‑classical photon statistics and entanglement. |
| 1990s–present | Single‑photon sources, quantum cryptography, quantum computing | Direct applications of photon quantum properties. |
| Phenomenon | Wave Description | Particle Description |
|---|---|---|
| Interference & Diffraction | Superposition of EM fields; intensity (\propto | E |
| Photoelectric Effect | Not explained by classical wave theory. | Photon transfers its entire quantum (h\nu) to an electron; kinetic energy (K = h\nu - \phi). |
| Compton Scattering | Classical Thomson scattering predicts wrong wavelength shift. | Photon collides with an electron, conserving energy & momentum → wavelength shift (\Delta\lambda = \frac{h}{m_ec}(1-\cos\theta)). |