Team: Dinh Cong Huy Nguyen Thai Long Bui Viet Hung Nguyen Duc Nam HUT- 17/10/2008 Gratings and application Mechatronics Engineering- Advanced Training Program • Grating: a system of multi close equidistant and parallel lines or bars, especially lines ruled on a polished surface, used for producing spectra by diffraction called also diffraction grating. • Diffraction grating: is an optical device used to learn the different wavelength or color contained in a beam of light. The device usually consist of thousand of narrow, closely spaced parallel slits (or grooves). Figure 1: - Diffraction grating: is an optical device used to learn the different wavelength or color contained in a beam of light. The device usually consist of thousands of narrow, closely spaced parallel slits (or grooves). - Used for producing spectra.(Fig 1) I- INTRODUCTION Fig 2: The first diffraction grating was made by Fraunhofer (which is called Fraunhofer diffraction). II- Background of topic  1. Single – slit diffraction.  2. Double- slits diffraction.  3. Multi- slits diffraction.  4. Diffraction gratings.  5. Quiz. II- Background The smaller the slit, the broader the entire the diffraction pattern. 1. Single slit diracon: Phenomena: the beam spreads out vercally aer passing through the slit. Denote: a- the width of the slit d- the distance between slit and screen θ - the angle between the perpendicular to the slit a line from the center of the slit to a point P on the screen Condition for dark fringe: sin m a λ θ = m= 1,2,3… m m y d a λ = 2 sina π β θ λ = ( ) ( ) 2 2 0 0 sin sin / sin( / 2) / 2 sin / a I I I a π θ λ β β π θ λ           = =           Posion of the mth dark fringe: The phase di'erence between the phase of light of the upper and lower trip: The intensity : 2.Double slits diffraction: Diffraction envelope Inference fringe - must consider not only diffraction due to the individual slits but also the interference of wave coming form different source. -intensity: 2 2 0 sin( / 2) cos 2 / 2 I I φ β β   =     2 sin d π φ θ λ = Where: is the phase di'erence at point P of 2 incident lights, and is calculated by the formula: φ 2 sina π β θ λ = And : is the phase di'erence of wave at P from the top trip with respect to the wave received from the bo*om trip: β 3.Multiple slits diffraction: - Constructive interference occurs for rays at angle θ satisfy: d.sinθ=mλ (m= 0,±1,±2,±3…) - The maxima are the same position as for two slits diffraction with the same spacing d. Q: Why occurs such this coincidence ?