Billet's split-lens experiment is a classic method to produce two coherent sources for interference.

Question

Billet's split-lens experiment is a classic method to produce two coherent sources for interference. A converging lens of focal length $f = 10$ cm is cut exactly in half along a plane containing its optical axis. A small, opaque black plate of thickness $\delta = 1$ mm is placed between the two half-lenses to separate them. A point-like source emitting monochromatic light of wavelength $\lambda = 0.5 \mu m$ is placed on the optical axis at a distance $p = 20$ cm in front of the lens. A screen is placed at a distance $H = 50$ cm behind the lens, perpendicular to the optical axis.

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