Thin films of YBa2Cu3O7-δ (YBCO) have been grown by pulsed laser deposition in a low-pressure background (10 -4-10-3 Torr) by using a pulsed, high intensity jet of O2 or N2O for oxidation. The oxygen source is provided by a pulsed molecular beam valve, and the opening of the valve and the triggering of the laser are synchronized with appropriate delay so that the supersonic gas jet and the ablated fragments arrive at the substrate at the same time. This provides the necessary oxygen to form the YBCO phase while maintaining a low oxygen background. The YBCO phase is not formed if the oxygen pulse is provided either before or much after the arrival of the ablation fragments at the substrate. The ability to grow superconducting films at low background pressures should allow usage of in situ analysis techniques, such as reflection high-energy electron diffraction, during pulsed laser deposition.