1 Brilliant Pattern Problem Problem Suspend a water drop at the lower end of a vertical pipe. Illuminate the drop using a laser pointer and observe the pattern created on a screen. Study and explain the structure of the pattern Suspend a water drop at the lower end of a vertical pipe. Illuminate the drop using a laser pointer and observe the pattern created on a screen. Study and explain the structure of the pattern

2 Overview Hypothesis Hypothesis Assumption of Experiment Experimental Setup Experimental Setup Devices and Process Investigations Investigations Experimental Results Theory Theory The Physics Behind Brilliant Pattern Conclusion Conclusion

3 Hypothesis Effects of reflection and refraction Diffraction Geometrical Optics + Physical Optics d/2 a

4 Experimental Setup Laser Pointer 10 mw, 532 nm, Radius: 1.45 mm 1 mm 35 cm

5 Observation

6 42 o 51 o Observation

7 Theory Passing through water drop (0 o )

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9 Snell’s Law

10 Traveling backwards (180 o ) Theory

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12 0o0o 42 o 51 o Experimental Results

13 Experimental Video

14 Distance between water drop and screen 4 m Water Droplet Radius: 0.9~2 mm Laser Pointer Diameter: 2.2 mm Wavelength: 532 nm Experiment 2: Physical Optics

15 Experiment 2: Physical Optics Diffraction

16 Theory Huygens’s Principle Every point on a propagating wavefront serves as the source of spherical secondary wavelets, wavelets, such that the wavefront at some later time is the envelope of these wavelets

17 Theory Huygens’s Principle Every point on a propagating wavefront serves as the source of spherical secondary wavelets, wavelets, such that the wavefront at some later time is the envelope of these wavelets

18 a Bessel Function

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20 Theoretical Analysis 0.9 mm 1.2 mm 1.5 mm 2.0 mm Diameter of water drop:

mm1.2 mm1.5 mm2 mm Theoretical Analysis Diameter of water drop:

mm 1.2 mm 1.5 mm 2 mm Experimental Results 0.9 mm 1.2 mm Experimental Results 1.5 mm 2 mm

23 Experimental Results 0.9 mm 2 mm

Geometrical Optics: – – At 0 o the light passes through the water droplet and is magnified – The light is reflected and refracted by the water droplet; thus, interference is demonstrated – At other degrees because the light beam has attenuated its energy so patterns are unable to be observed Wave Optics: – – Due to Huygens’s principle, light is diffracted, so diffraction bands are observable – As water droplets are enlarged the distance between each band decreases Conclusion

25 Thanks for your attention

26 Conclusion Geometrical Optics: – – At 0 o the light passes through the water droplet and is magnified – – At 180 o the light is reflected and refracted by the water droplet; thus, interference is demonstrated – – At other degrees because the light beam has attenuated its energy so patterns are unable to be observed Wave Optics: – – Due to Huygens’s law, light is diffracted, so diffraction bands are observable – – As water droplets are enlarged the distance between each band decreases