Laser Magnetic Field Measurement

The measurement of smallest magnetic fields is very difficult. The commonly used method relies on SQUIDs (superconducting quantum interference devices) that are based on superconducting material. Since superconductivity is observed only at very low temperature – even “high temperature superconductivity” is observed only below 150 K (-123°C) – these detectors are complicated and expensive. Over the last two decades, another technique was invented and turned out to be very promising. This technique uses a sample of atoms within a glass cell and a laser beam to optically pump the atoms into a special magnetic state. This way one can “polarize” the atoms to a very high degree such that their magnetic moments point into a certain direction. A second laser beam with linear polarization is sent through the sample. Depending on the atomic polarization, the laser polarization experiences a rotation (“non-linear magneto-optical rotation”) which can be detected precisely. A magnetic field – e.g. the one that is to be measured – will lead to disturbance of the atomic polarization and can hence be measured.