Quantum Nature of Light (Quantum Optics) Pham Tan Thi, Ph.D Department of Biomedical Engineering Faculty of Applied Sciences Ho Chi Minh University of Technology Courtesy of N Brunner and J Simmonds Light behave like a wave or a particle (This is called the duality of the behavior of light) Wave Characteristics Electrically Charged Particles and Electromagnetic Waves Electrons have (-) charge Protons have (+) charge Both have electric fields +- attract ++ and repel • The changing position of a charged particle creates “waves” called electromagnetic waves • The electromagnetic waves travel through empty space eventually interacting with a distant charged particle • Visible light is an electromagnetic wave Magnetism (Effect on electric charges) Moving electric charges also produce magnetic fields Example: electric current passing through a coil Another interesting example: the Earth’ magnetic field is produced by the spinning of charges in the liquid metal core of the Earth Conversely, magnetic field force charged particles to move… Accelerated Charges (electrons, protons) Produce (Ripples in the Electromagnetic Field) An electromagnetic wave is composed of two oscillating fields, and electric field and a magnetic field perpendicular to each other Antenna receives electromagnetic signal from TV station Wavelength of Electromagnetism means COLOR The Temperature Scale (Conversion from wavelength/energy to temperature) The scale mostly used in sciences, physics and astronomy is Kelvin The unit is Kelvin (K) Thermal Radiation • The fundamental sources of all electromagnetic radiation (EMR) are electric charges in accelerated motion • All bodies emit electromagnetic radiation as a result of thermal motion of their molecules This radiation, called thermal Reference #1 of different radiation, is a mixture wavelengths • Thermal radiation is emitted by all objects above absolute zero (-273.15°); but some of objects is in visible Reference #2 An electric heating element emits primarily infrared radiation But if its temperature is high enough, it also emits a discernible amount of visible light What is a Blackbody A blackbody is an idealized object that absorbs all EMR that falls on it - no EMR passes through it and none is reflected (i.e perfect emitter and perfect absorber) Because no light (visible EMR) is reflected or transmitted, the object appears black Leave appears green because green color is reflected to human eye .. .Light behave like a wave or a particle (This is called the duality of the behavior of light) Wave Characteristics Electrically Charged Particles... • All bodies emit electromagnetic radiation as a result of thermal motion of their molecules This radiation, called thermal Reference #1 of different radiation, is a mixture wavelengths • Thermal... position of a charged particle creates “waves” called electromagnetic waves • The electromagnetic waves travel through empty space eventually interacting with a distant charged particle • Visible light