To optimise combustion in a wide field of applications, lasers represent attractive future alternative ignition sources, especially for internal combustion engines. Experiments were carried out in a high pressure, constant volume chamber (up to 25 MPa peak pressure and initial temperature of 473 K). Laser induced ignition of different hydrogen-air mixtures (air/fuel equivalence ratio lambda = 1.8-8) was investigated, using different filling pressures (p = 0.5-4.2 MPa), different ignition energies (pulse energy PE = 1-50 mJ), different chamber temperatures (T = 393-473 K) and different focal length lenses (f = 60, 120 mm). A Q-switched Nd:YAG laser at 1064 nm with a pulse duration of about 5 ns was used for ignition. An InGaAs photodetector (800-1800 nm) and a piezoelectric pressure transducer were used to characterise the combustion. Gas mixtures between lambda = 2.5 and 3.6 showed knocking combustions. With increasing initial pressures the minimum pulse energy was decreasing. (C) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.