[en] There has been a growing interest in laser ablation of a graphite target in liquid phase aiming at the growth of polyynes, which are hardly produced employing conventional organic synthesis methods. Hydrogen-capped polyynes, (H(C ≡ C)_nH), are linear carbon chain molecules consisting of sp hybridized orbitals, being observed in the interstellar space. Due to their typical one-dimensional electronic structures, polyynes have attracted considerable attention in their size-dependent band gap and nonlinear optical properties. Large polyynes with n ≥ 5, in particular, have been prepared by laser ablation of graphite mostly in organic solvents, while we present experimental results on the formation of C₁₀H₂ (namely n = 5) by laser irradiation of a graphite target in neat water. Although larger polyynes can be formed in organic solvents, laser ablation in water has a unique advantage in that it can greatly reduce the contaminant carbon materials including graphite and graphite-like carbon particulates (in short, carbon contaminants hereafter) compared to the organic solvents