Two-photon absorption enables terahertz control of lattice modes in centrosymmetric materials.

Scientists want to understand how low-energy light interacts with materials that have symmetric atomic structures. In these materials, collective atomic vibrations normally do not interact directly with electric fields from terahertz light, a type of invisible radiation. To solve this mystery, researchers studied a material called 1T-TaS2. This material passes through three distinct ordered electronic states: commensurate, nearly-commensurate, and incommensurate charge-density-wavecharge-density-waveA state where electrons form a periodic pattern, altering material structure. phases. The team hit the material with both single-cycle and multi-cycle terahertz light pulses and tracked how it responded. They found that transitions between the material's phases leave clear signatures in the response. They also discovered that a two-photon absorptiontwo-photon absorptionA process where a material absorbs two photons simultaneously to reach a higher energy state. process drives the vibrations, showing how light can steer these atomic motions.

Why it matters

This helps researchers study material vibrations more precisely using low-energy light. It could lead to new methods for controlling material properties without high-power lasers.

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