Spectropolarimetry is a technique used to measure the polarization of light. It can be used to study the properties of materials, such as their optical activity, and to detect the presence of weak magnetic fields.
When light waves travel through a medium, they are sometimes scattered off particles in the medium. This scattering can cause the light waves to become polarized – that is, the electric field vector of the waves will tend to line up in a particular direction. The degree of polarization depends on the properties of the scattering particles and on how they are oriented with respect to the incident light.
Polarized light can be analyzed using a polarimeter. This instrument consists of two crossed Nicol prisms, which split incoming light into two beams that travel perpendicular to each other. These beams are then passed through a analyzing stage, where their polarization states are determined. The output from the polarimeter can be displayed on an oscilloscope or recorded for later analysis.
Spectropolarimetry is a powerful tool for studying astronomical objects. By measuring the polarization of starlight, astronomers can learn about the physical conditions in stellar atmospheres and distinguish between different types of stars. For example, spectropolarimetry was used to discover that some stars have strong magnetic fields (known as magnetic white dwarfs).
Magnetic fields also play an important role in accretion disks around black holes and neutron stars; by measuring polarized emission from these disks, astronomers can probe how matter behaves in extremely strong gravitational fields.