function alpha=alpha_mol(T,P,wavel)
  N0=2.55e19; %standard concentration
  T0=288; %standard Temperature
  P0=1013.25 %standard pressure (hPa)
  pnv=[0.029,0.028,0.027,0.025]; %molecular depolarization
  wv=[355,532,1064,2051];
  
  pn=interp1(wv,pnv,wavel,'cubic','extrap');
  n0=1+1e-8*(6432.8 + 2949810/(146-(wavel^-2)) + 25540/(41-(wavel^-2)))
  
  N=N0*(T0*P)/(P0*T);
  alpha=(3/8*pi)*(pi^2)*N*((n0^2)-1)^2 *(6+3*pn)*(N0^-2)*(wavel^-4)*((6-7*pn)^-2);
  
endfunction
