The primary heat source in most infrared spectrometers is the reference laser which typically produces 7 to 9 watts of waste heat for its one milliwatt optical output. The heat capacity of air (effectively the same as that of N₂) is approximately 1 Joule/gram-°C, or 1 J/liter-°C. The waste heat is sufficient to heat 1 liter of air by 9 °C per second! (Remember that the temperature difference between the two arms of the interferometer should be < 0.01°C). The waste heat was trapped away from the critical beam paths by foam baffles.