Question

Light from a helium-neon laser ($\lambda =633nm$) is incident on a single slit. What is the largest slit width for which there are no minima in the diffraction pattern?

Short answer

The largest width for$a<633\mathrm{nm}$in the diffraction pattern

Step-by-step solution

Helium-neon laser

Helium-neon (He-Ne) lasers are often used for interferometry because they are inexpensive and produce a consistent, visible output. They operate at a wavelength of $633nm$by default, although customized versions with outputs at various visible and infrared wavelengths are also available.

Step2: 

The angles within which dark fringes are detected in a single-slit experiment are given by

$\sin {\theta }_p=\frac{p\lambda }{a}$

where $a$ is the slit width and $p$ is the order To avoid dark fringes on the screen, the sine must be higher than $1$, which means that

$\frac{\lambda }{a}>1$

Rearrange this,

$a<\lambda$

By this,

$a<6.33·{10}^{-7}\mathrm{m}$