Abstract: The disclosure provides an improved fiber optic cable assembly that can protect spectrometers against one or more of the external noise and discharge sources. The improved fiber optic cable assembly provides electrical isolation and/or insulation (EII) protection for optical instruments, such as a spectrometer, in which the fiber optic cable assembly is terminated. The EII protection can include one or more of a non-conductive sheathing at least partially covering the termination and the sheathing, a dielectric break providing electrical isolation between the termination and the sheathing, an isolation boot, and a grounding tether. In one example a fiber optical cable assembly includes: (1) a termination, (2) sheathing, and (3) a dielectric break providing electrical isolation between the termination and the sheathing. A fiber optically coupled system having an improved fiber optic cable assembly is also disclosed.

Abstract: A configurable hybrid superheterodyne spectrum analyzer for deriving process state parameters from detected modulated light emitted by a plasma receives and conditions the electric signals converted from the modulated light for subsequent superheterodyne mixing at a specific intermediate frequency (IF) that is lower than the frequency of the modulated light. Signal conditioning includes filtering noise, aliasing and DC and/or amplifying or de-amplifying the signal. Once mixed, the superheterodyne signal is further filtered by an IF filter to define the signal bandwidth characteristics relevant to the process state parameters. The IF filter may configurably employ multiple filter functions such as Gaussian filtering of increasing widths and/or comb filtering for multiple passbands in the frequency spectrum. Finally, the IF mixed and filtered signal is digitized with respect to the specific intermediate frequency using an IF digitizer.