The instrument was purged with dry, CO₂ -free air while the data in this slide and the next were recorded. This interferogram was recorded from a model rocket igniter mounted at the source location, 660 ms after ignition. The burning was quite erratic as can be seen from the interferogram baseline. The time interval shown is 6 milliseconds, so the fluctuations have components up to at least 1 kHz. At a conventional scan velocity, these fluctuations would have a disastrous impact on the SNR. The same measurement approach was tried with gunpowder but the experiment fizzled. The 6 millisecond interval corresponds to 166 scans per second, or 5000 rpm operation.