Copper Reflectivity: What Thickness is Necessary?

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In summary, the question is about the necessary thickness of copper for achieving optical reflectivity. The answer is typically around 10 times the skin depth, but this contradicts a previous result that states the power dissipated per unit surface area is equal to (H^2)/2sigma*delta. This result suggests that the energy reflected from the surface of the conductor is independent of the depth of the copper, but considering a highly polished surface, both effects may not be completely at odds. Only some of the optical energy will be reflected, regardless of the copper's thickness, and the rest will be transmitted or absorbed. The amount absorbed and reflected can be reconciled by considering the surface finish.
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sachi
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We have a question that asks us what thickness of copper is necessary to achieve optical reflectivity. I know that the answer is just basically several times the skin depth (says 10 times). the only problem is that this contradicts a previous result that I've seen. We can prove that when a wave is incident on a metallic surface that the power dissipated per unit surface area is equal to (H^2)/2sigma*delta

where sigma is the conductivity and delta is the skin depth. We get this by integrating the poynting vector at z=0. This seems to suggest that the energy reflected from the surface of the conductor is independent of the depth of the copper, so surely it shouldn't matter thow thick the actual layer of copper is?
thanks for your help.
 
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It seems that the surface finish will have a large effect on the amount of reflected optical energy. But assuming that the surface is highly polished, then maybe the two effects that you mention are not completely at odds. Only some of the optical energy will be reflected, regardless of how many skin depths deep the copper is. If the copper is only 1 skin depth thick, then some of the optical energy gets transmitted, some gets absorbed, and some gets reflected. If the copper is many skin depths thick, then none gets transmitted, some gets absorbed and some gets reflected. Can you reconcile the amount absorbed with the amount reflected?
 

1. What is copper reflectivity?

Copper reflectivity refers to the ability of copper to reflect light, especially in the visible spectrum. This property makes copper a popular choice for use in mirrors and other reflective surfaces.

2. How is copper reflectivity measured?

Copper reflectivity is typically measured using a spectrophotometer, which measures the amount of light reflected off of a surface. The percentage of light reflected is known as the reflectivity percentage.

3. What thickness of copper is necessary for optimal reflectivity?

The thickness of copper necessary for optimal reflectivity depends on the wavelength of light being reflected. Generally, thinner layers of copper (less than 1 micrometer) are more reflective at shorter wavelengths, while thicker layers (greater than 100 micrometers) are more reflective at longer wavelengths.

4. How does the thickness of copper affect its reflectivity?

The reflectivity of copper increases as the thickness of the copper increases, up to a certain point. After this point, the reflectivity begins to decrease due to interference effects between the reflected waves. This is known as the critical thickness.

5. What factors can affect the necessary thickness of copper for optimal reflectivity?

The necessary thickness of copper for optimal reflectivity can be affected by factors such as the purity of the copper, the surface roughness, and the angle of incidence of the light. Additionally, the type of coating or treatment applied to the copper can also impact its reflectivity.

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