Let's experiment with the laser pointer!
Make a small slit on the wall (interval d) that does not allow light to pass through, and consider how the light passing through the slit interferes with each other by injecting parallel light. As shown in the figure, parallel light is incident on the vertical wall from the left. Assume that the light emitted from the slit to the right is a spherical wave using the slit as a light source. The light emitted from the slit strengthens or weakens each other according to the direction (φ), but as shown in the figure, if the optical path difference d sin φ of the light (electromagnetic wave) is an integer multiple of the wavelength λ, they strengthen each other (d sin φ = nλ: n is an integer). If it is an integer + 0.5 times, it just offsets.
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The laser light emitted by the laser pointer has a single wavelength, propagates in one direction (plane wave), and has the same phase, so interference is prone to occur. A Green laser pointerwith a wavelength of λ = 532 [nm] is used here. Of course, the same experiment can be performed with a commercially available red laser pointer, so if you have one, please try it. The measurement object is CD (compact disc). As shown in the figure, the data is recorded on the recording surface of the CD with a single stroke like a mosquito coil. This is called a truck. Seen in cross section, this truck has a slightly protruding shape. In fact, this track is intermittent, which corresponds to digital data, but the intermittent orbit is ignored here. The track pitch is set to 1.6 [μm]. Let's measure this track pitch.
2021-10-11 12:00:15
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