function output = deflection(input,a1,a2,b,n1,n2);


% DEFLECTION calculates the deflection caused by three planar surfaces that
% are oriented in order at angles a1, b, and a2 wrt the vertical direction.
% a1 and a2 are measured as positive for cw rotations and b is measured as
% positive for ccw rotations.  INPUT is the direction of the input beam
% measured wrt the horizontal direction and OUTPUT is the direction of the
% output beam meaured wrt the horizontal direction.
% R. Victor Jones, Harvard University, 12-15-00


%===================================
%
a1 = pi * a1/180;
a2 = pi * a2/180;
b = pi * b/180;
input = pi * input/180;
t1 = asin((1/n1)*sin(input+a1))-a1;
t2 = asin((n1/n2)*sin(t1-b))+b;
t3 = asin((n2)*sin(t2+a2))-a2;
output = 180 * t3/pi;