two-photon spectroscopy

Two-photon spectroscopy is a technique used in molecular spectroscopy that involves the absorption of two photons to excite a molecule to a higher energy state. This process is distinct from single-photon absorption, where only one photon is required for excitation.1

In two-photon spectroscopy, two photons, each with half the energy of the required transition, are absorbed simultaneously by the molecule. This method allows for the study of electronic transitions that are otherwise forbidden or weak under single-photon excitation. The use of lasers, particularly tunable dye lasers, is crucial for two-photon spectroscopy due to the need for high-intensity, narrow-banded radiation. This technique offers advantages in terms of resolution and sensitivity, enabling the investigation of molecular energy levels and structures with greater detail.123