= Solution
Decreasing the source diameter increases <spatial optical coherence> and moves the illumination towards the coherent on-axis limit. Here the grating frequency is only
$$
f=1/(800\ \mathrm{nm}),\qquad
\frac f{f_c}=\frac{193}{1.35(800)}\simeq0.179.
$$
The zero and first orders are comfortably within the pupil for on-axis illumination. Reducing an extended source can prevent some off-axis source points from losing <diffraction> orders at the pupil edge, and can therefore \b[increase the grating modulation, or leave it approximately unchanged if the relevant orders were already fully passed]. It need not give a universal numerical increase: higher orders, source shape, <defocus> and <optical aberrations> matter for a binary grating.
The resist's $\gamma$ and critical modulation $M_c$ in part (i) are material/process properties and \b[do not change merely because the source becomes smaller]. What may change is part (ii)'s comparison between the actual image modulation and $M_c$. If the improved image exceeds about 0.667, an exposure window opens; the source information alone does not establish a new numerical value.
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