Transient Grating Spectroscopy
Transient grating spectroscopy (TGS), also known as a laser-induced transient grating (LITG) technique, is a non-destructive pump-probe technique that utilizes laser interference instead of a single laser beam to excite a sample for evaluating exciton lifetime and diffusion coefficient.
In this case, two interfering laser beams create a standing wave on the surface of the sample, forming a transient grating. The depth of absorption modulation is measured by a delayed probe beam, diffracting from the grating. The modulation depth decays as quasiparticles propagate along the excitation density gradient. The rate of decay corresponds to the diffusion of the quasiparticles. By varying the grating period, detailed information on propagation dynamics can be obtained.
Moreover, LITG enables direction-dependent measurements of exciton diffusion in anisotropic materials. It is proven to be fully applicable for studying exciton and charge dynamics in crystalline media, such as bifluorene single crystals. The information on the directionality of exciton diffusion is essential for optimizing crystal orientation in various devices, e.g., crystal-based organic lasers.
LITG can be implemented using a HARPIA-TG transient grating spectrometer, which can be pumped by PHAROS and CARBIDE femtosecond lasers. Light Conversion has adapted its high-level mechanical and optical engineering solutions, which were gathered over almost 30 years of experience in the field of lasers and laser systems, to offer a simple, fully automated, and user-friendly transient grating spectroscopy system.
The principle of a LITG measurement.
