Errors and noise in laser-recoil measurements

A study of noise and error sources encountered during development of a laser-recoil test capability is reported. The laser-recoil technique is a method of evaluating the response of a burning energetic material to fluctuations of radiant heat flux, usually supplied by a laser. The technique involves measuring the extremely small recoil force imparted as the burning gases leave the surface. This technique offers the advantages of small sample size, reduced cost, and potentially improved accuracy over the existing acoustic T-burner technique but has the disadvantage of high sensitivity to noise because of the small magnitude of the recoil force to be measured. Noise sources identified include electrical ground loops, thermal drift, structural vibrations, acoustics, and low-frequency atmospheric pressure variations. Remedial changes reduced the overall noise level by a factor of five and extended the usable measurement range from 200 to 700 Hz. Tests and analyses of several potential errors are discussed, including demonstration of linear behavior at input heat-flux modulation levels up to 25%.