Faraday Rotation - The Budker Group法拉第旋转Budker组.pptVIP

Faraday Rotation Theory, Application, and Issues With a neat Tangent Zachary Marshall Faraday Rotation First noticed in 1845 by Michael Faraday Linearly polarized light near resonance travels through a material (esp. alkali metal gas) in a B-Field The B-Field must have a component in the direction of propagation. Polarization rotates He wrote in his notebook, I have at last succeeded in illuminating a magnetic curve or line of force and in magnetising a ray of light Some Hand Waving Applied magnetic field creates Zeeman splitting of energy levels LHC and RHC polarized light see different scattering cross-sections, so different refractive indices, and so have different phase velocities Their different propagation means the linear polarization of light rotates Again, with Math Zeeman shift changes resonance by gFm0Bz Dq = V B L Dq = p (n- - n+) L / l Dq = CRb L [alkali] B / Dl2 n = S pi c2 ni Faraday Rotator / Isolator Optical element rotating the polarization of light Polarizer - Faraday Rotator – Polarizer Prevents contamination and “backsplash” of electromagnetic waves Common materials for use in 700-1100 nm range: terbium doped borosillicate glass and terbium gallium garnet crystal (TGG). They can be magnetized before hand. For Measuring Number Density Cell filled with a gas, at least some of which is an alkali metal (usually below its boiling point) Tunable laser (e.g. Ti:Saph) through the center of a cell What could possibly go wrong? Optical pumping during measurement Laser heats the cell interior Thermal fluctuations in a cell Remember: What ever can go wrong, will go wrong. But there are ways around each problem. How else could we find [Rb]? Here comes the thermo… Killian Equations First developed in the 1920’s, credit is usually given to Killian (1926). d(ln P)/dT = DH/(R T2) (Clausius-Clapeyron) In a small range, DH is temp. invar. Resulting equation is of the form log P = A + B/T Additional terms like C log T, D / T2 are common So What are A a