What is light? Light as an electromagnetic wave Light as a particle, the photon Phys 1970B Introductory Optics Brown University Lecture by Rudolf Oldenbourg 4 February 2009 electromagnetic field the current i increases the charge on the condenser plates the increasing charge increases the electric field E between the plates the increasing E -field generates a magnetic field B the current i also generates a B field around the wire In this example the E-field is generated by charges on the condenser plates In the next example of an oscillating dipole we will find that time varying E and B fields can sustain themselves in the form of an electromagnetic wave electric field of an oscillating dipole the far field of an oscillating dipole is an electromagnetic wave characteristics: amplitude, frequency, phase, wavelength, speed wavelength Sources of light thermal or black body radiation accelerating charge chemical reactions excited atoms, molecules Thermal radiation Random motion of atoms I black body Synchrotron radiation DESY Hamburg, Germany National Synchrotron Lightsource, Brookhaven NY Aurora Fluorescent light bulb Atomic excitation Frauenhofer lines Fluorescence fluorescein molecule single molecule fluorescence light is a particle photon counting photon counting noise photon counting Bibliography Many images are taken from the book by E. Hecht, Optics, Addison-Wesley, 4th edition Other sources: