Optical double slit experiment

In a double slit experiment, waves pass through two narrow slits that are spaced a distance $d$ apart. The interference pattern is observed on a screen that is a distance $L$ from the slits. When visible light is used to perform a double slit experiment, the frequency is so high that it is only possible to measure the intensity of the interference pattern. Typically, a laser shines on a glass plate that has a thin metal layer on it. Two thin slits are etched in the metal. The wavelength of light is usually hundred od nanometers, the distance between the slits $d$ is typically a few microns, and the distance $L$ to the screen where the intensity is measured is often meters.

The intensity pattern is displayed on the right. Try some other wavelengths and slit spacings.

 

$d$

= 100 μm

$L$

= 2 m

$\lambda$

= 650 nm

The small divisions on the scale on the right represent mm.

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In the Far field: $L >> d >> n\lambda$

Constructive interference $r_2-r_2=d\sin\theta \approx d\frac{y}{L}=n\lambda$  $n\in$ integers

Destructive interference $r_2-r_2=d\sin\theta \approx d\frac{y}{L}=\left(n+\frac{1}{2}\right)\lambda$  $n\in$ integers

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