## Category Archives: physics

### the Gaussian beam (interactive)

The Gauss­ian beam “is a con­ve­nient, wide­spread model in laser optics.” [1] It is indeed con­ve­nient that such a math­e­mat­i­cally rel­a­tively sim­ple model can describe the evo­lu­tion of laser light in free space so well. Given the wave­length of the laser, it can be described by a sin­gle para­me­ter. This can be either the beam

### the Doppler effect (relativistic)

Chris­t­ian Doppler in 1942 pre­dicted the Doppler effect for all kinds of waves, not only sound waves. The Doppler effect for light was demon­strated in 1948 by Fizeau. In con­junc­tion with the arti­cle on the clas­si­cal Doppler effect, as it occurs e.g. for sound waves, we will here exam­ine the rel­a­tivis­tic Doppler effect which is

### the Doppler effect (classical)

The Doppler effect is noth­ing really new. It’s well-known that Doppler fre­quency shift occurs for sound as well as light; there are, how­ever, some sub­tle dif­fer­ences between the two, owing mainly to Einstein’s spe­cial the­ory of rel­a­tiv­ity. This arti­cle describes the clas­si­cal Doppler effect as it occurs e.g. for sound waves and in which the