Step-scan Michelson Fourier-transform spectrometer for optical emission spectroscopy in UV-VIS spectral range.

We present the design, construction, and first spectra of a step-scan Michelson Fourier-transform spectrometer for optical emission spectroscopy in the UV-VIS spectral range. The mirror motion mechanism is based on a long-travel piezo-based linear translation stage with built-in position feedback. The step-scan arrangement allows for signal integration, making the instrument suitable for measurements of less intensive radiation sources and for the photon-counting technique. The spectrometer consists of two coupled Michelson interferometers, one for the spectrometer itself and the other to provide positional reference for the mirror stepping mechanism using interference fringes of a stabilized 635 nm laser diode. Using interpolation of the laser interferogram and taking advantage of the translation stage precision in linear-piezo mode, the mechanism is capable of performing 79 nm steps, which puts the Nyquist wavelength at ∼320 nm. The spectrometer was tested by measuring the spectra of HgAr cold-cathode fluorescent lamp and electron-induced fluorescence of ambient air. Two different detectors were used, an amplified photodiode detector and a photomultiplier tube module in photon counting mode. The highest achieved experimental spectral resolving power was ∼4000 using 1 mm of total mirror travel and the highest achieved noise-free dynamic range was 10. Test results show that the instrument is suitable for use with moderate-to-low intensity signal sources such as small gas discharges and spectroscopic measurements at astronomical telescopes.