When it is reflected interference occurs, the waves overlap and diffraction patterns become visible. What happens when you laser scan a CD or DVD?Īs the laser beam is focused directly on the CD or DVD the laser beam is reflected. Step 2: Recording data to determine the width of the tracks in the CD. After marking the pattern use a ruler to measure the distance between maxima and record the values as your ∆x value. How to measure ∆x value in laser diffraction?įocus the laser through the diffraction grating and while it is on, mark and draw the diffraction pattern onto the paper. Next, draw/mark the diffraction pattern on the paper and measure the distance between the two maxima. While the laser is focused on the CD measure the height at which the laser’s light hits the CD and record it. How do you find the diffraction pattern on a CD?įor a CD the diffraction pattern would appear on the paper, this is why the lab is set up this way. Using commercial electronic storage devices like CDs and DVDs as gratings rather than commercially produced plan transmission gratings enhances student interest in the activity and also opens up… Why use CD’s and DVDs as diffraction gratings?ĬDs and DVDs contain regularly spaced micrometer sized features which can act like a diffraction grating. Digital data are encoded by means of pits on the recording layer of the disc. Analog information is converted into digital information, which is then encoded onto the disc from the inside edge out. Because DVD uses a higher sampling rate and can store more information, it produces a richer, fuller sound and delivers a video image that’s twice as clear as VHS.ĭVD (digital video disc) is a technology based on optical data storage similar to compact disc (CD). The same size as a CD-ROM, DVD offers many advantages over CD and videotape. What is the main advantage of using DVDs instead of CDs? It is possible to put a large number of scratches per centimeter on the material, e.g., the grating to be used has 6,000 lines/cm on it. How do you make a diffraction grating?Ī diffraction grating is made by making many parallel scratches on the surface of a flat piece of transparent material. It is the pattern of these pits burned onto a disc’s surface that encodes the 1’s and 0’s a player translates into sound and/or images.ĭiffraction grating, component of optical devices consisting of a surface ruled with close, equidistant, and parallel lines for the purpose of resolving light into spectra. When it is reflected interference occurs, the waves overlap and diffraction patterns become visible.ĭigital versatile discs (DVDs) can store more information than compact discs (CDs) because they have smaller pits, placed closer together. As the laser beam is focused directly on the CD or DVD the laser beam is reflected. How do CD’s and DVD’s use diffraction gratings?Īns: In CDs or DVDs, the discs themselves act as the diffraction gradient for the laser beam. The combination of the two makes the CD or DVD a reflective grating. There is also a reflective metal coating on top of this groove pattern. A DVD can hold nearly 7 times as much data as a CD, because the tracks are closer together.Ĭan a digital versatile disk behave like a grating element?Įxplain why the CD or the DVD acts like a transmission grating? The CDs and DVDs have spiral grooves cut on the disk space running from the inner edge to the outer edge. How does a CD work as a diffraction grating?Īlthough a CD is not really a diffraction grating, after all the light bounces off of the CD, it does not pass through it, the CD acts like a diffraction grating because the reflected light undergoes constructive and destructive interference due to the special geometry of the CD’s bottom surface.ĭVDs and CDs reflect a colorful spectrum because their tracks act like reflection diffraction gratings.
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