The Full Form of TRFR is Time-Resolved Faraday Rotation.

Time Resolved Faraday Rotation (TRFR) is an optical pump-probe technique used to detect electron spin precession about an external magnetic field in semiconductors.

For over thirty years, silicon based electronics have continued to progress as advances in
lithography have allowed circuit elements to grow geometrically smaller and correspondingly faster. However, the increasing difficulty at which this performance is achieved has
motivated the development of technologies which exploit quantum behavior. One such
avenue is an electron spin-based technology, or “Spintronics.” Spin is environmentally robust and offers long-lived (tens of nanoseconds) macroscopic quantum behavior compared
with many other solid-state quantum variables. In fact, magnetic bits in hard drives are
now based on the giant magnetoresistive effect, which is a spin-polarized resistivity. This
field hopes to further exploit spin for computational elements.

Wolf’s recent Science article [1] on spintronics points out that development of magnetoelectonics requires measurements of tiny magnetic moments of very small devices on very
short time-scales, and Faraday rotation of a linearly polarized light pulse by a coherent
collection of electron spins has begun to fulfil this need. Faraday rotation is a phenomenon
by which the linear polarization of a electric field directed along k through a magnetized
medium will be rotated by an amount proportional to the component of magnetization
along k. This rotation is caused by the magnetic field’s generation of different indices
of refraction for left and right circularly polarized light, as shown in Figure 1. The two
components of the circular decomposition of a linear polarization travel with different
phase velocities, and after leaving the medium, have acquired a phase difference between
them, causing the linear polarization to rotate. Furthermore, the presence of unequal
populations of photoexcited carriers in the two spin states (σ+ and σ−) affects the indices
of refraction unequally and so leads to Faraday rotation effects.