As mentioned in Table IV and Table V, three positions along-slit are covered (FOV position row 20, 200, 380) by six monochromator scans (seven for the boresight position) for the VISNIR channel. The same three positions along-slit for the IR channel are covered, but only two scans below 2700 nm are available due to the significant thermal emissions at higher wavelengths. As distinct trends are observed between LDO and IAS data sets, we report the FWHM separately derived from each data set (Fig. 14).

[Figure: Fig. 14. LDO- and IAS-based FWHM vs wavelength. (A) Evolution of the FWHM across the spectral range of the VISNIR channel for the data acquired at LDO and IAS for FOV position 20. The sampling (green dashed line) is shown to highlight any potential correlation with the FWHM. (B) Same as (A) but for position 200. (C) Same as (A) but for position 380. (D) Same as (A) but with all FOV positions of the IR channel.]

For the VISNIR channel, the FWHM measured at LDO is well within requirements but is significantly lower (10 to 40%) than the FWHM measured at IAS. The difference is more significant for low (<1000 nm) and high (>1700 nm) wavelengths.
We hypothesize that this discrepancy is primarily related to the fact that the entire entrance baffle of MAJIS was illuminated at IAS while this was not the case at LDO. More straylight was observed with the entirely illuminated entrance, which is consistent with the wider spectral dispersion observed with the IAS setup.. The FWHM difference between IAS and LDO appears to increase as we move away from the center columns and the middle of the FOV. This difference is maximum at wavelengths <1000 nm. This is consistent with the straylight observed on MAJIS (less straylight in the FOV center than on its edges and straylight maximum at <1000 nm 11). As MAJIS entrance baffle will also be fully illuminated at Jupiter, this suggests that the actual performances of MAJIS will be more similar to those measured at IAS than those measured at LDO. The IASbased FWHM is slightly out of specification at short wavelengths. We have also explored the possibility that IAS OP1 monochromator FWHM may have been wider than expected (up to 2 nm instead of 0.7 nm for VISNIR wavelengths, as discussed in a companion paper5). The lowest difference between IAS and LDO is observed at 1400 nm for position 20 (Fig.
14.A): the difference between LDO (FWHM 3.85 nm) and IAS (FWHM 4.15 nm) requires a monochromator FWHM of 1.55 nm, which could be consistent with this putative wider IAS OP1 FWHM. However, in most cases, differences would require that the IAS OP1 monochromator FWHM was well above 2 nm, in particular for wavelengths <1000 nm, where the contribution 28 of the straylight remains the most plausible explanation.

Finally, we note that there is no obvious correlation between the sampling and the FWHM of the VISNIR channel.
For the IR channel, fewer measurements are available (only 2 per FOV position). However, no significant difference between IAS and LDO data is observed, and the measurements are compliant with the requirements. No definitive conclusion can be made for higher wavelengths due to the lack of measurements. Still, given the low FWHM variation across 300 nm, the substantial margin between the performances and the requirements at low wavelength, and the absence of stray light for the IR channel, it is anticipated that the FWHM will meet the requirements across the entire IR spectral range.