Evaluation of the LLNL Spectrometer for Possible use with the NSTec Optical Streak Camera as a Light Gas Gun Diagnostic

In fiscal year 2012, it was desired to combine a visible spectrometer with a streak camera to form a diagnostic system for recording time-resolved spectra generated in light gas gun experiments. Acquiring a new spectrometer was an option, but it was possible to borrow an existing unit for a period of months, which would be sufficient to evaluate both “off-line” and in-gas gun shots. If it proved adequate for this application, it could be duplicated (with possible modifications); if not, such testing would help determine needed specifications for another model. This report describes the evaluation of the spectrometer (separately and combined with the NSTec LO streak camera) for this purpose. Spectral and temporal resolutions were of primary interest. The first was measured with a monochromatic laser input. The second was ascertained by the combination of the spectrometer’s spatial resolution in the time-dispersive direction and the streak camera’s intrinsic temporal resolution. System responsivity was also important, and this was investigated by measuring the response of the spectrometer/camera system to black body input—the gas gun experiments are expected to be similar to a 3000K black body—as well as measuring the throughput of the spectrometer separately over a range of visible light provided by a monochromator. The flat field (in wavelength) was also measured and the final part of the evaluation was actual fielding on two gas gun shots. No firm specifications for spectral or temporal resolution were defined precisely, but these were desired to be in the 1–2 nm and 1–2 ns ranges, respectively, if possible. As seen below, these values were met or nearly met, depending on wavelength. Other performance parameters were also not given (threshold requirements) but the evaluations performed with laser, black body, and successful gas gun shots taken in aggregate indicate that the spectrometer is adequate for this purpose. Even still, some (relatively minor) opportunities for improvement were noticed and these were documented for incorporation into any near-duplicate spectrometer that might be fabricated in the future