Analysis of Variables in Thin Film Reflection
Taylor Wrobel
MSE 3803
What was Done in Lab 8
The Blue Morpho Butterfly
Wing Structure
Multi-Layer Reflection
Wing reflects light at each layer of chitin
Reflected light gives the wing color
Characteristics of Wing Color
Purely Reflected Light
All color caused by reflection
When back-lit, wing is brown, and nearly transparent
Pearlescent
Viewing angle changed color
Colors ranged from dark blue, to near white.
Dependent on Refractive Index
Refractive index of the medium impacted color
In air (n = 1.001) In IPA (n = 1.37)
Exploring Wing Characteristics Through Simulation
Free Snell
Free software written in Scheme
Simulates light passing through layers
Controllable Variables
Substrate Refractive Index
Medium Refractive Index
Incident Angle
Number of Substrate Layers
Depth of Substrate Layers
Wing Sim
Application written to simplify simulation
Simulation Results
AND
Effects of Variables
Effect of Incident Angle
Simulation parameters constant apart from angle
Angle changed between 0 (normal) and 90 degrees (tangent)
10 degree increments
Total of 10 simulations
Angle Results
Effect of Number of Layers
Simulation parameters constant apart from number of layers
Number of layers changed between 10 and 100
10 layer increments
Total of 10 simulations
Number of LAyers Results
Effect of Layer Depth
Simulation parameters constant apart from layer depth
Layer depth changed between 90nm and 140nm
10nm increments
Total of 6 simulations
Layer Depth Results
Effect of Index of Refraction
Simulation parameters constant apart from medium refractive index
Substrate refractive index kept as chitin, n=1.57
Index changed between n=1.0 and n=2.0
Increments of 0.1
Total of 11 simulations
Refractive Index Results
Implications
As the medium and substrate refractive indices near each other, the spectrum darkens
If the indices were the same, it would reflect no light
This would require a fluid of around the same refractive index of chitin, n=1.57
Very few fluids have refractive indices that high, but silicon oil (n=1.52) may work
An Idea for Thought
A solution of arsenic trisulfide and sulfur in methylene iodide has a very high refractive index (n=1.9 approx)
With this high of an index used as a medium:
Resultant reflected spectrum would have same rough intensity as the spectrum in air
However, intensity would be centered around 660nm, producing a vibrant red.
References
Park, J.O. and Srinivasarao, M. (2013). MSE 3803 Class Materials. Georgia Tech School of Material Science.
Mohan Srinivasarao, "Nano-Optics in the Biological World: Beetles, Butterflies, Birds, and Moths", Chem. Rev., 99, 1935 (1999).
The FreeSnell Thin-Film Optical Simulator