Slow light propagation via saturable absorption of acetylene in hollow-core photonic crystal fiber

We report experimental results on saturable absorption of acetylene (C 2 H 2 ) confined to a hollow-core photonic crystal fiber (PCF). In our experiments, we utilized a 3-m long PCF with a 10-μm hollow core coupled to SMF-28 pigtails at both ends. The 30–70-ns laser pulses of the Watt scale peak power at the wavelength λ = 1528.015 nm of the P5 line of ν 1 + ν 3 combinational band of acetylene were used. The saturation power at the center of the Doppler broadened (≈520 MHz) absorption line was observed to grow in the range 0.15–1.2 W in the acetylene pressure interval 0.07–0.7 mbar which was evaluated from the cell optical absorption. The slow light propagation of the 30-ns saturating laser pulses with maximal fractional delay of ≈0.1 was experimentally observed. Optimal input pulse power in this experiment grew with the cell optical density following growth of the saturation power.