Measuring the Diameter of a Human Hair by Laser Diffraction Introduction Often it is necessary to determine the diameter of a fine wire, thin thread or other object that cannot be measure by convectional means. These items can be measured by using methods of diffraction and interference known as Young’s Double Slit Experiment. While Young’s experiment deal with the pattern of light impinging on two narrows slits separated by a small distance, the method can by applied to an object with a small diameter as well. Where the diameter is within an order of magnitude of the wavelength of laser light used. Procedure 1) Take a 15 cm by 15 cm piece and make a 10cm by 10cm hole in the center of the cardboard piece. This is your mounting bracket. 2) Select one strand of hair approximately 15-25cm long. This hair needs to be mounted on the mounting bracket from step 1.