Large area 3D helical photonic crystals
(Color online) Definitions of the plane wave beam incidence angles in the air and in the photoresist.
(Color online) Cross-section of a 3D pattern and period definitions.
Latent image in the photoresist after (a) 1st exposure, (b) rotate 60° + 2nd exposure, (c) rotate additional 60° [120° total] + 3rd exposure, (d) rotate additional 60° [180° total] + 4th exposure, (e) rotate additional 60° [240° total] + 5th exposure, (f) rotate additional 60° [300° total] + 6th exposure. (Model parameters: ψ = 45°, θD = 8°, φ = 60°, nr = 1.7, λ = 355 nm, threshold = 70%). Light gray: photoresist surface, dark gray: photoresist cross-section at boundary.
(Color online) 3D IL accessible PhC parameter space (n PR/n ∼ 1.3).
(Color online) Experimental setup for 3D IL. The beam uses TE polarization, such that the linear polarized light is in the plane of the paper.
Close up of 3D photonic crystal models, made using 6-exposure interferometric lithography. Each image is 3 μm on edge, Az = azimuth & El = elevation of image plane. (Model parameters: ψ = 45°, θD = 8° φ = 60°, N = 6, nr = 1.7, λ = 355 nm, threshold = 62%).
(Color online) Helical 3D IL PhCs made using six exposures with 60° rotation. (a) Mathematical simulations; (b) SEM images of experimental structures. (Model parameters: ψ = 45°, θD = 8° φ = 60°, N = 3, nr = 1.7, λ = 355 nm, threshold = 62%).
(Color online) Helical PhC degree of polarization (DOP) measurements. The average value of 1-DOP is 3.7% for the 3D PhC.
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