Less beam power can improve fringe visibility

Two coherent beams separately give 36 and 4 W/m². An ideal attenuator reduces only the stronger beam until the two intensities match.

By what factor does fringe visibility increase?

Organize the givens & assumptions

Initial intensities = 36, 4 W/m²
Final intensities = 4, 4 W/m²

Same-frequency coherent beams, parallel polarization, same observation medium and unchanged individual detector intensities, unless the prompt explicitly averages phase.

A $3/5$
B $5/3$
C $3$
D $9$

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