SOLID HYDROGEN FOR NONLINEAR OPTICS

We recently developed a new method of preparing a parahydrogen crystal which is suitable for experiments on nonlinear optical processes. The crystal was grown slowly from pressurized liquid-phase in order to av oid internal stress from the thermal constriction, and was cooled down to 4.2 K. The obtained crystal was uncracked and perfectly transparen t with a high damage threshold. To evaluate the quality, the vibration al coherence decay was measured using the time-resolved coherent anti- Stokes Raman spectroscopy (CARS) technique. The decay process showed a nonexponential behavior, with an asymptotic limit characterized by a single time constant of 2.6 mu s, which corresponds to a linewidth of less than 0.1 MHz. This decay time is extremely slow compared to the p reviously published work.