Update README.md

README.md

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 # Gaussianoptics
 
 Python library for the simulation of gaussian beams according to ray optics.
+
+You can build an optical bench with the following elements (see test.py for an example):
+-    'path', refractive index , position[mm], (relative: 'r', absolute: 'a' (position is the end position), filling: 'f')
+-    'thinlens', f [mm] , position[mm], (relative: 'r', absolute: 'a')
+-    'thicklens',  	[   n1 = refractive index outside of the lens,
+                       n2 = refractive index of the lens itself (inside the lens),
+                       R1 = Radius of curvature of First surface,
+                       R2 = Radius of curvature of Second surface,
+                       t = center thickness of lens] , position[mm], (relative: 'r', absolute: 'a')
+-    'flatmirror', 0 , position[mm], (relative: 'r', absolute: 'a')
+-    'curvedmirror', [R [mm],
+                     angle [°],
+                     plane (0=tangential, 1=sagittal)], position[mm], (relative: 'r', absolute: 'a')
+-    'flatrefraction', [    n1 = initial refractive index,
+                           n2 = final refractive index] , position[mm], (relative: 'r', absolute: 'a')
+-    'curvedrefraction', [  n1 = initial refractive index,
+                           n2 = final refractive index,
+                           R = radius of curvature R > 0 for convex (centre of
+                           curvature after interface)], position[mm], (relative: 'r', absolute: 'a')
+
+
+example: opticalbench = ['path',1,0.050,'a''thinlens',0.05,0.100,'r''path',[1,0,0,0,0],0,'f''thinlens',[0.15,0,0,0,0],0.200,'r']
+
+TODOs:
+- check if 'path' is first and last element
+- find 'empty space'
+- normalize curve by refractive index other than 1