We have studied the structure and oxygen incorporation in YBa2Cu3O7- delta thin films during in situ formation by pulsed laser deposition. A quenching technique has been used for the first time to freeze the nature of in situ films immediately on termination of growth. In situ resistance and transition-temperature measurements, and X-ray diffraction studies on undoped and Ag-doped films, have shown that an oxygen-deficient orthorhombic phase is indeed possible during growth due to the presence of atomic and ionized oxygen species in the laser-induced plasma.