Zernike Polynomials

The Zernike module provides tools for working with Zernike polynomials, which are commonly used to represent optical aberrations in microscopy PSF models.

Conventions

This module uses the following conventions:

• Noll Indexing: All functions use the Noll single-index scheme, starting from 1
• RMS Normalization: Polynomials are normalized to have RMS = 1 over the unit circle
• Units: Coefficients typically represent wavefront error in units of wavelength

Core Types

The ZernikeCoefficients type is the main container for Zernike polynomial coefficients, used to represent both phase and amplitude aberrations:

# Create coefficients for 15 Zernike terms
zc = ZernikeCoefficients(15)

# Access and modify directly using Noll indices
zc.phase[4] = 0.5  # Add 0.5λ RMS of defocus
zc.phase[11] = 0.2  # Add 0.2λ RMS of spherical aberration

Core Functions

The Zernike module provides several core functions for working with Zernike polynomials:

• zernikepolynomial(n, l, ρ, θ): Compute the Zernike polynomial with radial order n and azimuthal frequency l at polar coordinates (ρ, θ)
• radialpolynomial(n, m, ρ): Compute just the radial component of a Zernike polynomial
• evaluate_pupil(coeffs, grid_size): Generate a complex pupil function from Zernike coefficients

Analysis Functions

Additional utility functions for analyzing Zernike coefficients include:

• rms(coeffs): Calculate RMS values for magnitude and phase coefficients (excluding piston)
• significant_terms(coeffs, threshold): Return list of significant terms above a threshold

Index Conversion

Functions for converting between different Zernike indexing schemes:

• noll2nl(j): Convert from Noll single index to (n,l) indices
• nl2noll(n, l): Convert from (n,l) indices to Noll single index
• noll2osa(j): Convert from Noll to OSA/ANSI index
• osa2noll(j): Convert from OSA/ANSI to Noll index
• nl2osa(n, l): Convert from (n,l) indices to OSA/ANSI single index
• osa2nl(j): Convert from OSA/ANSI single index to (n,l) indices

Common Zernike Polynomials

The table below shows the relationship between Noll indices, (n,l) pairs, and common aberration names:

Visualizing Zernike Polynomials

using MicroscopePSFs.Zernike
using CairoMakie
function evaluate_polynomial_grid_nl(n::Integer, l::Integer, grid_size::Integer=201)
    j = nl2noll(n, l)
    coeffs = ZernikeCoefficients(j)
    coeffs.mag[1] = 0.0 # was set to 1 by default
    coeffs.mag[j] = 1.0
    field = evaluate_pupil(coeffs, grid_size)
    result = real.(field)
    return result
end

function plot_zernike_nl_grid(max_n::Integer=4)
    fig = Figure(size=(1000, 180 * max_n))
    burd = reverse(cgrad(:RdBu))

    for n in 0:max_n
        l_start = -n + (mod(-n, 2) != mod(n, 2) ? 1 : 0)
        l_values = l_start:2:n
        row = n + 1
        for (col_idx, l) in enumerate(l_values)
            j = nl2noll(n, l)
            ax = Axis(fig[row, col_idx],
                aspect=DataAspect(),
                title="j=$j, (n=$n, l=$l)",
                xticklabelsize=0,
                yticklabelsize=0,
                yreversed=false)
            z_data = evaluate_polynomial_grid_nl(n, l, 201)
            max_val = maximum(abs.(z_data))
            min_val = -max_val
            heatmap!(ax, range(-1, 1, length=size(z_data, 1)),
                range(-1, 1, length=size(z_data, 2)),
                z_data',
                colorrange=(min_val, max_val),
                colormap=burd)
            hidedecorations!(ax)
        end
    end
    return fig
end
fig = plot_zernike_nl_grid(5)
save("zernike_polys.png",fig)

This visualization shows the first 21 Zernike polynomials laid out in a grid. Each plot is labeled with both its Noll index j and the corresponding (n,l) indices. Red regions represent positive values, blue regions represent negative values, and white represents zero. Posiive y axis is up to match Wikipedia.

Usage in PSF Models

The Zernike module is primarily used for representing aberrations in PSF models:

# Create Zernike coefficients with 15 terms
zc = ZernikeCoefficients(15)

# Add some aberrations
zc.phase[4] = 0.5  # 0.5λ RMS of defocus
zc.phase[11] = 0.2  # 0.2λ RMS of spherical aberration

# Create a ScalarPSF with these aberrations
psf = ScalarPSF(1.4, 0.532, 1.518, coeffs=zc)

# Create a VectorPSF with these aberrations
vector_psf = VectorPSF(1.4, 0.532, base_zernike=zc, n_medium=1.33)

For a full API reference and details on all available functions, see the API Reference section.