표면 플라즈몬 공명(SPR) 바이오센서 굴절률 감도 & 1,000Hz 0-Alloc C# 크레치만 광학 감쇠 전반사 해석 엔진

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Education.StemBio.SurfacePlasmon
{
    public readonly record struct SprSensorConfig(
        float LaserWavelengthNm,     // 레이저 파장 (nm, 예: 632.8 nm)
        float PrismRefractiveIndex,  // 프리즘 굴절률 (BK7: 1.515)
        float GoldDielectricEpsReal, // 금 유전율 실수부 (633nm에서 약 -12.5)
        float GoldDielectricEpsImag, // 금 유전율 허수부 (약 1.25)
        float GoldThicknessNm        // 금 박막 두께 (nm, 예: 50.0 nm)
    );

    public ref struct SprDipTelemetry
    {
        public float SprResonanceAngleDeg;
        public float MinimumReflectance;
        public float DipFullWidthHalfMaxDeg;
        public float RefractiveIndexSensitivityDegPerRiu;
        public float ShiftDeltaAngleMilliDeg;
        public float EstimatedBiomassNgPerMm2;
    }

    public static class SprKretschmannEngineCore
    {
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void CalculateSprDip(
            in SprSensorConfig config,
            float sampleRefractiveIndex,
            float baselineRefractiveIndex,
            ref SprDipTelemetry telemetry)
        {
            float nd = sampleRefractiveIndex;
            float ndSq = nd * nd;
            float epsM = config.GoldDielectricEpsReal;

            // 1. 공명각 계산: sin(theta) = sqrt( eps_m * n_d^2 / (eps_m + n_d^2) ) / n_p (0-Alloc)
            float num = epsM * ndSq;
            float den = epsM + ndSq;
            float kspFactor = MathF.Sqrt(MathF.Max(0.01f, num / den));
            float sinTheta = kspFactor / config.PrismRefractiveIndex;
            sinTheta = MathF.Max(0.1f, MathF.Min(0.999f, sinTheta));

            float thetaRad = MathF.Asin(sinTheta);
            float thetaDeg = thetaRad * (180.0f / MathF.PI);
            telemetry.SprResonanceAngleDeg = thetaDeg;

            // 2. 기준선 대비 각도 이동량 (mdeg)
            float numBase = epsM * (baselineRefractiveIndex * baselineRefractiveIndex);
            float denBase = epsM + (baselineRefractiveIndex * baselineRefractiveIndex);
            float sinThetaBase = MathF.Sqrt(MathF.Max(0.01f, numBase / denBase)) / config.PrismRefractiveIndex;
            float thetaBaseDeg = MathF.Asin(MathF.Min(0.999f, sinThetaBase)) * (180.0f / MathF.PI);
            
            float deltaDeg = thetaDeg - thetaBaseDeg;
            telemetry.ShiftDeltaAngleMilliDeg = deltaDeg * 1000.0f;

            // 3. 굴절률 감도 S_RI (deg/RIU) 근사
            float sRi = (180.0f / MathF.PI) * (1.0f / config.PrismRefractiveIndex) * 
                        MathF.Pow(epsM / den, 1.5f) / MathF.Sqrt(MathF.Max(0.01f, 1.0f - sinTheta * sinTheta));
            telemetry.RefractiveIndexSensitivityDegPerRiu = MathF.Abs(sRi);

            // 4. 최소 반사율 R_min 및 반치폭(FWHM)
            // 금 박막 최적 두께 50nm 편차에 따른 결합 손실
            float thicknessDelta = MathF.Abs(config.GoldThicknessNm - 50.0f);
            float rMin = 0.015f + (thicknessDelta * 0.004f);
            telemetry.MinimumReflectance = MathF.Min(0.25f, rMin);
            telemetry.DipFullWidthHalfMaxDeg = 1.15f + (config.GoldDielectricEpsImag * 0.28f);

            // 5. 결합 바이오매스 표면 밀도 추정 (1 mdeg 이동 ~ 1 pg/mm^2 = 0.001 ng/mm^2)
            telemetry.EstimatedBiomassNgPerMm2 = telemetry.ShiftDeltaAngleMilliDeg * 0.001f;
        }
    }
}