The misalignment together with the presence of nitrogen causes a build-up of strain. At the sector interfaces there is a slight crystal-lattice misalignment, which allows for the incorporation of nitrogen (slightly absorbing, see intensity image). Usually very high irradiances from ultrashort laser pulses are required to create quarter-wave rotations.ħ Photo-elasticity: Strain-induced birefringenceĬlear plastic drawing device (“French curve”) between crossed polarizers Image fromĨ Strain-Induced birefringence in diamondĪn artificially grown diamond with nitrogen impurities between crossed polarizers The diamond is grown as sectors(right, lower left, upper left) from a tiny seed (in the centre). The AC Kerr Effect creates birefringence using intense fields of a light wave. Use the Kerr effect in isotropic media, where the Pockels' effect is zero. Where: Dn is the induced birefringence, E is the electric field strength, K is the Kerr constant of the material.
Light is unaffected by the Pockels’ cell and hence is passed by the polarizer.Ħ The Kerr effect: the polarization rotation is proportional to the Kerr constant and E2 Before switching After switching 0° Polarizer Mirror 0° Polarizer Mirror Pockels’ cell as wave plate w/ axes at ±45° Pockels’ cell as an isotropic medium Light becomes circular on the first pass and then horizontal on the next and is then rejected by the polarizer. The Pockels’ cell switches (in a few nanoseconds) from a quarter-wave plate to nothing. The pulse length is limited by the round-trip time of the laser and is usually ns long.ĥ The Q-Switch In high-power lasers, we desire to prevent the laser from lasing until we’ve finished dumping all the energy into the laser medium. 100% 0% Time Cavity Loss Cavity Gain Output intensity This yields a short “giant” high-power pulse. Preventing the laser from lasing until the flash lamp is finished flashing, and 2.
Vl/2 is called the half-wave voltage.Ĥ Q-switching Q is the Quality of the laser cavity. Where Dj is the relative phase shift, V is the applied voltage, and r63 is the electro-optic constant of the material. Rick Trebino Georgia Tech Ways to actively control polarization Pockels' Effect Kerr Effect Photo-elasticity Optical Activity Faraday Effect Jones Matrices Unpolarized light, Stokes Parameters, & Mueller Matrices frog/lecturesĢ The Pockels' Effect +V An electric field can induce birefringence.Įlectro-optic medium Transparent electrode Polarizer Analyzer +V The Pockels' effect allows control over the polarization rotation.ģ The Pockels Effect: Electro-optic constants
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