2DLightPathSimulator/LensSimulatorCore/Optical/Material.cs

namespace LensSimulatorCore.Optical;

public class Material
{
    public SellmeierCoefficients Sellmeier { get; set; }

    public double RefractiveIndex(double wavelength)
    {
        return Sellmeier.CalculateRefractiveIndex(wavelength);
    }
        
    private readonly Func<double, double, double, double> _reflectivity;
    private readonly Func<double, double, double, double> _transmissivity;

    public Material(SellmeierCoefficients sellmeierCoefficients)
    {
        Sellmeier = sellmeierCoefficients;
        _reflectivity = ComputeReflectivity;
        _transmissivity = (angle, n1, wavelength) => 1.0 - Reflectivity(angle, n1, wavelength);
    }

    private double ComputeReflectivity(double angleDegrees, double n1, double wavelength)
    {
        // Convert angle to radians
        var angleRadians = angleDegrees * Math.PI / 180.0;

        // Check for total internal reflection
        var criticalAngle = Math.Asin(RefractiveIndex(wavelength) / n1);
        if (angleRadians > criticalAngle)
        {
            return 1.0;
        }

        var rs = ComputeFresnelCoefficient(angleRadians, n1, wavelength, isSPolarized: true);
        var rp = ComputeFresnelCoefficient(angleRadians, n1, wavelength, isSPolarized: false);
        return (rs + rp) / 2.0;
    }

    private double ComputeFresnelCoefficient(double angle, double n1, double wavelength, bool isSPolarized)
    {
        double numerator;
        double denominator;

        if (isSPolarized)
        {
            numerator = n1 * Math.Cos(angle) - RefractiveIndex(wavelength) * Math.Sqrt(1 - Math.Pow((n1 / RefractiveIndex(wavelength) * Math.Sin(angle)), 2));
            denominator = n1 * Math.Cos(angle) + RefractiveIndex(wavelength) * Math.Sqrt(1 - Math.Pow((n1 / RefractiveIndex(wavelength) * Math.Sin(angle)), 2));
        }
        else
        {
            numerator = n1 * Math.Sqrt(1 - Math.Pow((n1 / RefractiveIndex(wavelength) * Math.Sin(angle)), 2)) - RefractiveIndex(wavelength) * Math.Cos(angle);
            denominator = n1 * Math.Sqrt(1 - Math.Pow((n1 / RefractiveIndex(wavelength) * Math.Sin(angle)), 2)) + RefractiveIndex(wavelength) * Math.Cos(angle);
        }

        return Math.Pow(numerator / denominator, 2);
    }

    // ReSharper disable once MemberCanBePrivate.Global
    public double Reflectivity(double angle, double n1, double wavelength)
    {
        return _reflectivity(angle, n1, wavelength);
    }

    public double Transmissivity(double angle, double n1, double wavelength)
    {
        return _transmissivity(angle, n1, wavelength);
    }
}