1. The problem statement, all variables and given/known data Light from a helium neon laser with wavelength 633nm is incident on a single slit. What is the largest slit width for which there are no minima in the diffraction pattern? 2. Relevant equations 3. The attempt at a solution For single slit diffraction, asin(theta)=p*lambda, where a= slit width, and p= 1,2,3... So I know that when the slit width is smaller than the wavelength, no minima occur, but ? what about when it is equal? I'll try out some numbers: say the slit width is 6.33e-7 m, the same as the wavelength. Then I will find the angular position of the first minimum: (6.33e-7)sin(theta)=(1)(6.33e-7)t theta has to be equal to 90 degrees, which I don't think can be possible. So the wavelength has to be less than 633 nm. Is this correct?