Method for manufacturing optical element

A method for manufacturing an optical element, comprising:

• in a heating process, heating a phosphate-based glass containing Bi2O3 in a proportion of 10 mass % or higher and 30 mass % or lower to a first temperature, the first temperature ranging from a temperature at which the glass viscosity is log η=9 [dPa·sec] to a temperature at which the glass viscosity is 10 [dPa·sec],
• in a pressing process, pressing the heated glass with an upper mold and a lower mold at the glass viscosity of log η=9 [dPa·sec] to 10 [dPa·sec] at a first pressure, the first pressure being in the range of 10 MPa or higher and 100 MPa or lower,
• in a pressure holding process, holding the glass pressed in the pressing process with the upper mold and the lower mold at a second pressure, the pressure holding process comprising a first period where the second pressure is held at the first temperature and a second period where the second pressure is held while and cooling the glass to a second temperature, the second temperature ranging from a temperature that the heated glass is pressed at the viscosity of log η=9 [dPa·sec] in the pressing process to a temperature at which the glass viscosity is log η=12 [dPa·sec],
• in a cooling process, after the pressure holding process, cooling the pressed glass, and in an extracting process, extracting the cooled glass from the upper mold and the lower mold,
• wherein from a time of bringing the glass into contact with a pressing surface of the mold to a time of the glass reaching the second temperature, one of the first pressure and the second pressure is applied to the glass, and
• wherein the second pressure is equal to or higher than a critical pressure of oxygen and equal to or lower than 10 MPa.