Nonstationary coherent optical effects caused by pulse propagation through acetylene-filled hollow-core photonic-crystal fibers

Abstract

Experimental observations of nonstationary coherent optical phenomena, i.e., optical nutation, free induction, and photon echo, in the acetylene (${}^{12}$C${}_{2}$H${}_{2}$) filled hollow-core photonic-crystal fiber (PCF) are reported. The presented results were obtained for the acetylene vibration-rotational transition $P$9 at wavelength 1530.37 nm at room temperature under a gas pressure of 0.5 Torr. An all-fiber pumped-through cell based on the commercial 2.6-m-long PCF with a 10-\ensuremath{\mu}m hollow-core diameter was used. The characteristic relaxation time ${T}_{2}$ during which the optical coherent effects were typically observed in our experiments was estimated to be \ensuremath{\approx}8 ns. This time is governed by the limited time of the acetylene molecules' presence inside the effective PCF modal area and by intermolecule collisions. An accelerated attenuation of the optical nutation oscillations is explained by a random orientation of acetylene molecules.