Classical history: 1678: Christiaan Huygens hypothesises light as a wave phenomenon. 1704: Isaac Newton publishes 'Opticks' - he believed light comprised particles. 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.
Quantum foundation: 1900: Max Planck quantises energy packets of e/m radiation to describe emission from warm objects. 1905: Albert Einstein invokes the photon of e/m radiation to describe the photo-electric effect in metals. 1923: Arthur Compton assigns the photon momentum to describe non-elastic scattering from electrons. 1924: Louis de Broglie assigns wavelength to particles, leading to the wave-particle duality concept. 1925: "Schrödinger Equation" describes the wave properties of particles, invoking quantum entanglement. 1927: Paul Dirac proposes quantisation of electromagnetic radiation fields. 1946/49: Richard Feynman with Tomonaga, Schwinger and Dyson develop quantum electrodynamics (QED) - a quantum/special relativity theory to describe e/m radiation interactions with matter. 1982: Alain Aspect demonstrates quantum entanglement in pair of photons.
Demonstrations of capabilities: 1900:
Waveband rebranding: Prior to 1960, the millimetre wave band was referred to as the high-frequency end of the microwave band and the terahertz region was called the far infrared band.
Increased activities in these parts of the electromagnetic spectrum led first to the emergence of the name "millimetre wave band" for the 30-300 GHz region, and then to the name "sub-millimetre wave band" for the range 300 GHz to 3 THz.
Post year 2001 the sub-millimetre wave band started to be referred to as the terahertz band, with definitions of the upper and lower bounds of this varying widely and being author dependent. Following this, the millimetre wave band started to be referred to as the sub-terahertz band.