Delayed optical nutation inside a hollow-core photonic crystal fiber filled with acetylene

Abstract

The delayed optical nutation effect has been used to evaluate the longitudinal relaxation time (T1) inside an acetylene-filled hollow-core photonic crystal fiber (HC-PCF) at room temperature. In this experiment, sequences of two short optical pulses of 30 ns and 15 ns in width, respectively, with the maximum peak power up to ∼2.5 W, were generated at a laser wavelength of 1530.37 nm, which corresponds to the acetylene ro-vibrational P9 absorption line. The gas pressure inside the 1 m-long HC-PCF varied in the range 0.1–1 Torr. Numerical simulations based on the optical Bloch equations allowed us to evaluate the longitudinal relaxation time as T1∼9ns, proving to be fundamentally limited by the transit-time broadening. Also, the obtained results revealed the influence of slow and fast molecules in the form of a non-exponential decay of the delayed-nutation signals.