Optics / Interactive experiment
Cure depth & reflection.
Give light a second pass. Explore how a mirror beneath an absorbing material changes the power deposited through its depth.
Controls.
Drag a slider or enter an exact value.
Two passes, one profile.
- Total
- Downward
- Reflected
Depth z (mm) · surface at 0, mirror at d
Where the energy lands.
- With mirror
Depth z (mm) · surface at 0, mirror at d
How uniform is the exposure?
- With mirror
UV–Vis absorbance A (unitless)
This sweep holds thickness, reflectance, and cuvette path length fixed.
More absorption, up to a point.
- With mirror
- Current α
- Optimum
Absorption coefficient α (mm⁻¹)
Local power density at z = d, with I₀, d, and R held fixed.
The best absorption at the bottom
- Optimal α (mm⁻¹)
- —
- Equivalent UV–Vis A
- —
- Maximum bottom power (mW/mm³)
- —
- Current bottom power (mW/mm³)
- —
Pbottom = α I₀ (1 + R) e−αd
For nonzero illumination, the maximum is at α* = 1/d, with A* = L / [ln(10) d].
This optimizes local power at the bottom surface. This is also the minimum through the material in this model.
Download the MATLAB calculation ↓The model
How light deposits energy.
As light passes through the material, some of its energy is absorbed. A mirror sends the remaining light back through for a second pass. The model adds the two beams to calculate how much power is absorbed at each depth.
Follow the two passes
Depth z is measured from the top surface. The mirror sits at z = d, where d is the material thickness. I₀ is the intensity entering the material, and R is the fraction reflected by the mirror.
- Light traveling down
- Idown(z) = I₀ e−αz
- Light returning from the mirror
- Iup(z) = R I₀ e−α(2d − z)
- Power absorbed at each depth
- Pabs(z) = α [Idown(z) + Iup(z)]
Intensity measures power passing through an area, in mW/mm². Multiplying by α gives the power absorbed per unit volume, in mW/mm³.
From absorbance to absorption
The UV–Vis measurement A describes how much light is lost over a known measurement path L. The absorption coefficient α expresses that loss per millimeter:
A larger α means energy is absorbed over a shorter distance. This deposits more energy near the surface, but leaves less light to reach the bottom.
Read the results
Uniformity compares the lowest absorbed power with the highest. A value of 100% means every depth receives the same power per unit volume. With no illumination or no absorption, both are zero and this ratio is undefined.
Power absorbed in material is the fraction of incoming power absorbed over both passes:
What this model describes
The calculation treats the material as uniform, with a constant absorption coefficient. Light enters perpendicular to the surface and reflects once from the bottom mirror. Scattering, reflection at the top surface, and interference are omitted.
The result is deposited optical power. To predict which regions cure, you would also need the exposure time and the material’s curing threshold.
Adapted from Hunter Whaples’ MATLAB model, Cure Depth – Reflector, October 22, 2026.