Method and apparatus for improved process control and real-time determination of carbon content during vacuum degassing of molten metals

A method for degassing molten metal in a melt chamber, the method comprising:

• depressurizing the melt chamber to a substantially vacuum pressure;
• projecting a first portion of an optical beam generated by a laser source through a volume of gases evolved from the melt chamber, the volume of gases including at least one indicator gas;
• detecting the first portion of the optical beam after the first portion has passed through the volume of gases;
• projecting a second portion of the optical beam through a reference volume of gases, the reference volume of gases comprising the at least one indicator gas;
• detecting the second portion of the optical beam after the second portion has passed through the reference volume of gases;
• based on the detected first and second portions of the optical beam, controllably changing an output frequency of the laser source to substantially correspond with an absorption line of the at least one indicator gas;
• determining a real-time concentration of the at least one indicator gas based on the detected first and second portions of the optical beam;
• determining a process time for degassing, based on the real-time concentration;
• and
• re-pressurizing the melt chamber upon completion of the process time.