You get a summer internship working with a 589.2nm laser (an intense light source with a very well defined wavelength). You want to spray some oil with noil=1.25 on your glasses with nglass=1.50 as an additional safety feature to protect you from accidental flashes of laser light.
a) Graphically visualize how you can make a thin film that reflects the given laser wavelength.
To visually understand how to make a thin film that reflects the given laser wavelength, we can use the concept of constructive interference. Constructive interference occurs when two waves align in such a way that their crests and troughs line up, resulting in a wave with larger amplitude.
To create a thin film that reflects the specific laser wavelength of 589.2 nm, we need to consider the conditions for constructive interference between the incident laser light and the reflected light.
Here's how you can graphically visualize the process:
Step 1: Draw a horizontal line to represent the surface of the thin film. Label it as the "Film Surface."
Step 2: Draw a vertical line coming down from the "Film Surface" and label it as the "Reflected Light." This line represents the path of the reflected laser light.
Step 3: Measure a distance on the "Reflected Light" line that corresponds to the wavelength of the laser light. In this case, the laser light wavelength is 589.2 nm. Since we want to create a film that reflects this wavelength, mark a point on the "Reflected Light" line at a distance of 589.2 nm from the "Film Surface." Label this point as "Point A."
Step 4: Draw another line, starting from "Point A," at an angle of 90 degrees to represent the "Incident Light." The incident light is the incoming laser light that strikes the thin film.
Step 5: Measure a distance along the "Incident Light" line equal to the optical path traveled through the film. The optical path length is given by the equation: optical path length = thickness of the film * refractive index of the film.
In this case, we want to spray the oil with a refractive index of 1.25 on the glasses with a refractive index of 1.50. The difference in refractive indices creates a phase shift in the reflected light, leading to interference.
For example, assume the thickness of the film is "d." Multiply this value by the refractive index of the oil (1.25) to obtain the optical path length.
Step 6: Measure the optical path length along the "Incident Light" line, starting from "Point A" and label the new point as "Point B."
Step 7: Draw a line connecting the "Film Surface" and "Point B" to represent the "Travel Path of Light through the Film."
Step 8: Extend the "Travel Path of Light through the Film" line to intersect with the "Reflected Light" line. Label this point of intersection as "Point C." This represents the point where the reflected light path combines with the incident light path after passing through the film.
Step 9: Draw a line connecting "Point C" and the intersection of the "Reflected Light" line and the "Film Surface". This line represents the "Outgoing Reflected Light" from the thin film.
If the length of the "Outgoing Reflected Light" matches the length of the "Incident Light" path, constructive interference occurs, and the light is reflected.
By following these steps and visualizing the incident and reflected light paths, you can graphically understand how to create a thin film that reflects the given laser wavelength.