Laboratory Testing

Ensuring robust on-sky performance requires thorough characterization in the lab. To this end, DMD-MOS has been meticulously aligned, calibrated, and tested.

Results from Laboratory Testing

FWHM v. Detector Position X FWHM v. Detector Position Y

HgNe arc lamp spectra from 3 dotted vertical line slits (shorter ones on the left and right, longer slit in the middle). Each dot has a diameter of 3 micromirrors. The spectral- and spatial-direction FWHMs for the selected high-SNR lines are plotted over the original spectral channel image. In general, the spectral FWHM has a larger variation with FWHM values ranging from 2 to 5 pixels, the average FWHM for 546nm lines with SNR > 50 is 2.81 along spectral direction and 3.74 along spacial direction. From this image, we determine that the both direction FWHM variations are dominated by the wavelength dependency of the dispersion: shorter wavelengths correspond to larger FWHM while the central wavelength agrees with the expected spot size.

WL Calibration Arc Lamps Results from wavelength calibration tests after applying the wavelength solution. The DMD was configured to use a staircase shape slit with a width of 1.4 mirrors (square root of 2 as along the diagonal of the micro-mirrors). Due to the actuation axis of our DMD’s micromirrors, the DMD must be placed at a 45 degree angle to correctly send light into the two channels. As a result, the slits are limited to diamond shapes. We tested both long-slit (roughly 20x1.4 micromirrors; resulting spectra shown above) as well as a circular aperture (not shown). We used Hg, Ne, Ar, Kr arc lamps for calibration. For this preliminary testing, a 3rd order polynomial fit was used to generate the wavelength solution, 90% of the residuals are within sub-pixel scale. This testing confirms the sensitivity of DMD-MOS to a wavelength range of 400-700nm.

LSF

Spatial and spectral line spread function (LSF) of the high-SNR 546nm Hg line from the previous figure. The Y mean shows the average intensity along the spectrally-collapsed line, while the X mean corresponds to the average along the spatially-collapsed line. These data show a Gaussian LSF in the spectral direction with a calculated FWHM of 2.58 px, in agreement with the design value. The intensity variation is about 4% of the total intensity. This analysis confirms our system is able to meet design goals.