4072
Co-axial measurements of infrared radiation emitted from the melt pool showed correlation to the presence of O2 or CO2 in the gas mixture .
 infrared, melt pool, CO2, gas
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 infrared, melt pool, CO2, gas