add a function to compute the refractive index of water as a function of wavelength

1 files changed, 30 insertions, 0 deletions

diff --git a/refractive_index.c b/refractive_index.c
new file mode 100644
index 0000000..d7d07f9
--- /dev/null
+++ b/refractive_index.c
@@ -0,0 +1,30 @@
+#include <math.h>
+#include "refractive_index.h"
+
+static double A0 = 0.243905091;
+static double A1 = 9.53518094e-3;
+static double A2 = -3.64358110e-3;
+static double A3 = 2.65666426e-4;
+static double A4 = 1.59189325e-3;
+static double A5 = 2.45733798e-3;
+static double A6 = 0.897478251;
+static double A7 = -1.63066183e-2;
+static double UV = 0.2292020;
+static double IR = 5.432937;
+
+double get_index(double p, double wavelength, double T)
+{
+    /* Returns the index of pure water for a given density, wavelength, and
+     * temperature. The density should be in units of kg/m^3, the wavelength in
+     * nm, and the temperature in Celsius. */
+    /* normalize the density, temperature, and pressure */
+    p = p/1000.0;
+    wavelength = wavelength/589.0;
+    T = (T+273.15)/273.15;
+
+    /* first we compute the right hand side of Equation 7 */
+    double c = A0 + A1*p + A2*T + A3*pow(wavelength,2)*T + A4/pow(wavelength,2) + A5/(pow(wavelength,2)-pow(UV,2)) + A6/(pow(wavelength,2)-pow(IR,2)) + A7*pow(p,2);
+    c *= p;
+
+    return sqrt((2*c+1)/(1-c));
+}