/usr/share/radiance/dichroic.cal is in radiance-materials 4R0+20110410-1build1.
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Approximate thin-film dichroic material
This formula is only correct at normal incidence
Feb 2004 G. Ward (funding provided by Visarc)
Usage:
void BRTDfunc matname
10
rrefl grefl brefl
rtrns gtrns btrns
0 0 0
dichroic.cal
0
15 0 0 0
0 0 0
0 0 0
film_thick_m film_n
subs_n subs_tr subs_tg subs_tb
}
{ Passed arguments }
film_thick = arg(10); { film thickness in microns }
film_n = arg(11); { index of refraction for thin film }
subs_n = arg(12); { index of refraction for substrate }
subs_tR = arg(13); { substrate transmission in red }
subs_tG = arg(14); { substrate transmission in green }
subs_tB = arg(15); { substrate transmission in blue }
{ Peak wavelengths for red, green, & blue (microns) }
WL_R : 0.595;
WL_G : 0.545;
WL_B : 0.445;
{ Reflection at first interface }
r1 = if(Rdot, (1 - film_n)/(1 + film_n),
(subs_n - film_n)/(subs_n + film_n));
{ Reflection at second interface }
r2 = if(Rdot, (film_n - subs_n)/(film_n + subs_n),
(1 - subs_n)/(1 + subs_n));
{ Reflection magnitude at substrate-air interface }
subs_r = sq((1 - subs_n)/(1 + subs_n));
{ Thin film penetration (approx.) }
L = film_thick / RdotP;
{ gamma expressions }
gammaR = 2*r1*r2*cos(4*PI/WL_R*film_n*L);
gammaG = 2*r1*r2*cos(4*PI/WL_G*film_n*L);
gammaB = 2*r1*r2*cos(4*PI/WL_B*film_n*L);
{ Reflection magnitude at film }
filmR = (r1*r1 + r2*r2 + gammaR)/(1 + sq(r1*r2) + gammaR);
filmG = (r1*r1 + r2*r2 + gammaG)/(1 + sq(r1*r2) + gammaG);
filmB = (r1*r1 + r2*r2 + gammaB)/(1 + sq(r1*r2) + gammaB);
{ Approx. reflection from either side }
rrefl = if(Rdot, filmR + subs_r*sq(subs_tR), subs_r + filmR*sq(subs_tR));
grefl = if(Rdot, filmG + subs_r*sq(subs_tG), subs_r + filmG*sq(subs_tG));
brefl = if(Rdot, filmB + subs_r*sq(subs_tB), subs_r + filmR*sq(subs_tB));
{ Approx. transmission }
rtrns = (1 - rrefl)*subs_tR;
gtrns = (1 - grefl)*subs_tG;
btrns = (1 - brefl)*subs_tB;
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