OH1 Organic THz Generation Crystal

Overview

OH1 is an organic electro-optic crystal used for high-field terahertz generation by optical rectification. Pumped by a near-infrared optical parametric amplifier it has produced peak terahertz fields in the tens of MV/cm, placing it among the strongest terahertz sources available from a table-top laser. It also works in reverse as an electro-optic sampling detector and as a second-harmonic generator.

Spectral coverage and what it means

OH1 concentrates its output in the 0.1 to 3 THz range rather than spreading it across a very wide band. For nonlinear terahertz spectroscopy that concentration is usually an advantage: the driving field at the frequencies of interest is higher than it would be with a broader emitter of the same total energy. If the experiment instead needs coverage above about 5 THz, DAST or DSTMS are the better match.

Pump requirements

Like DAST and DSTMS, OH1 is phase matched near 1.3 to 1.5 um and therefore needs an OPA or OPCPA in front of it. Groups running an Yb platform typically add a tunable OPA stage for exactly this purpose. If adding a conversion stage is not practical, BNA gives comparable generation behaviour while being pumped directly at 800 nm or around 1.03 um.

Handling and storage

Organic terahertz crystals are soft, hygroscopic and easily damaged. Store them sealed and dry, keep the mounted element inside a nitrogen or dry-air purge box during operation, and raise the pump fluence gradually while watching the terahertz signal rather than jumping straight to the target level. Never clean the crystal face with solvents, and always handle the part by its mount or substrate edge. Damage in organic crystals is usually cumulative rather than catastrophic, so a crystal that has been overdriven once will keep degrading.