Difraction

Diffraction
Introduction

Francesco Maria Grimaldi an Italian scientist was the first to observe and identify this phenomenon. When waves bend around objects specifically through a gap and spread out at the end this is known as diffraction. Light diffraction is only caused by a single slit and therefore is not the same as young's experiment which was done with a double slit. Diffraction does not change the wavelength as when light is made up of only one colour (monochromatic) then the bands it will produce will produce the same colour, red light produces a bigger pattern compared to blue light showing that diffraction rises with wavelength. Therefore, the pattern observed when using white light will contain bands (fringes) containing the spectrum of colours from red to violet. The amount it diffracts depends on the size of the wavelength of light passing through and the size of the gap its passing through.

http://www.bbc.co.uk/schools/gcsebitesize/science/images/ocr_phy_diffraction-wide.jpg

When waves diffract through a big gap they don’t spread out much as the light wavelength is smaller than the gap size.

http://www.bbc.co.uk/schools/gcsebitesize/science/images/ocr_phy_diffraction.jpg

As previously commented wavelength of light passing through also effects the amount it diffracts. A shorter wavelength gives less diffraction, this is significant for microscopes as diffraction causes image details to blur. The electrons in an electron microscope have a small wavelength and this can rectify the finer details as compared to light microscopes. This means we can improve resolution by using a different wavelength however we cannot eliminate diffraction because it is a natural result of the wave nature of light. Diffraction is also the reason we can get an enlarged image in a microscope. When a lens forms an image of an object the image is actually a tiny diffraction pattern. For a lens or any circular hole, the image of a point object will be made up of a circular central peak (called the diffraction spot) surrounded by faint circular fringes. The intensity of light in the diffraction pattern of a circular opening is a complex diffraction pattern (due to the fact that a circular opening can be viewed as a slit of varying widths).If two point objects are very close together, the diffraction patterns of their images will overlap. As the objects are moved closer together a point is reached where one can't tell if there are two overlapping images or a single image therefore a higher resolution is reached.