So I'm having some trouble with this problem.. Is there an equation or is it just a ratio? I'm having so many problems with this one!
THANKS!
What is the minimum thickness of coating which should be placed on a lens in order to minimize reflection of 531 nm light? The index of refraction of the coating material is 1.32 and the index of the glass is 1.57.
Read "single layer reflection coatings" at
http://en.wikipedia.org/wiki/Anti-reflective_coating#Single-layer_interference_coatings
You need 1/4 wavelength thickness at a refractive index of 1.32
At 531 nm and index 1.32, the wavelength of light is 531/1.32 = 412 nm
The coating thickness should be 1/4 of that
that's what i thought, too. but it's not.
2n(material)t= m*(wavelength/2)
going from a medium with higher n to lower n, you divide the wavelength by 2.
thanks for the help, though. i eventually figured it out!
To solve this problem, you need to consider the concept of optical interference. When light travels from one medium to another, part of the light is reflected and part of it is transmitted. The reflected light causes undesirable reflections, which can be minimized by using a thin film coating with a specific thickness.
To find the minimum thickness of the coating that minimizes reflection, you can use the equation for thin film interference:
2nt = mλ
Where:
n is the index of refraction of the coating material
t is the thickness of the coating
m is an integer representing the order of the interference fringe
λ is the wavelength of light
In this case, the problem specifies that the index of refraction for the coating material is 1.32, and the index of refraction for the glass is 1.57. The wavelength of light is given as 531 nm.
To find the minimum thickness, you need to find the smallest integer value of m that satisfies the equation.
Let's plug in the values:
2 * (1.32) * t = m * (531 nm)
Since we want to minimize reflection, we are interested in the first-order minimum (m = 1). Solving the equation for t:
t = (m * λ) / (2 * n)
t = (1 * 531 nm) / (2 * 1.32)
t ≈ 201.705 nm
Therefore, the minimum thickness of the coating should be approximately 201.705 nm in order to minimize reflection of 531 nm light.