DescriptionPrism compressor curve.svg	Effective pathlength for a prism compressor with A = 100 mm, θ = 55°, and α = 10°. The colors correspond to different values of B, where B = 67.6 mm means that the beam barely hits the tips of both prisms at refractive index 1.6.
Date	9 July 2006
Source	This W3C-unspecified plot was created with Gnuplot.
Author	Han-Kwang Nienhuys

Hankwang, the copyright holder of this work, hereby publishes it under the following licenses:

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	Attribution: Hankwang
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	This licensing tag was added to this file as part of the GFDL licensing update.http://creativecommons.org/licenses/by-sa/3.0/CC BY-SA 3.0Creative Commons Attribution-Share Alike 3.0truetrue

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License. Subject to disclaimers.http://www.gnu.org/copyleft/fdl.htmlGFDLGNU Free Documentation Licensetruetrue

This file is licensed under the Creative Commons Attribution 2.5 Generic license.

Attribution: Hankwang

You are free:

• to share – to copy, distribute and transmit the work
• to remix – to adapt the work

Under the following conditions:

• attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.

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Gnuplot script

Created with the following Gnuplot script (also by Han-Kwang and also GFDL/CC-By licensed)

# Calculate path lengths at different refractive indices in a prism compressor with a given geometry.
# Copyright Han-Kwang Nienhuys, 2006
# Licensed for distribution and modification according to the GFDL or CC-By licenses
# (which means basically: with proper attribution to the author)
pi=4*atan(1)
d2r=pi/180
sind(x)=sin(x*d2r)
cosd(x)=cos(x*d2r)
tand(x)=tan(x*d2r)
asind(x)=asin(x)/d2r

beta(n,alpha,theta)=asind(sind(alpha+theta)/n)
gam(n,alpha,theta)=theta-beta(n,alpha,theta)
delta(n,alpha,theta)=asind(n*sind(gam(n,alpha,theta)))

l1(n,alpha,theta,A)=A/cosd(delta(n,alpha,theta))     # pathlength through air
C(n,alpha,theta,A,B)=B-A*tand(delta(n,alpha,theta))
Bmin(n,alpha,theta,A,B1)=B1+A*tand(delta(n,alpha,theta))

# pathlength through 2nd prism. Undefined if the ray misses the prism.
l2(n,alpha,theta,A,B)=C(n,alpha,theta,A,B) < 0 ? 1/0 : C(n,alpha,theta,A,B)*sind(alpha+theta)/cosd(beta(n,alpha,theta))

D(n,alpha,theta,A,B)=l2(n,alpha,theta,A,B)*cosd(gam(n,alpha,theta))/sind(theta)
l3(n,alpha,theta,A,B)=D(n,alpha,theta,A,B)*sind(alpha+theta)

# A=distance between prism surfaces
# B=distance between prism tops (measured parallel to surface)
# theta=prism top angle
# alpha=indicent angle
# n=refractive index
pathlen(n,alpha,theta,A,B)=2*(l1(n,alpha,theta,A,B)+n*l2(n,alpha,theta,A,B) - l3(n,alpha,theta,A,B))
# difference with reference index n0. Specify B1 as distance from top where the n0
# ray hits prism 2.
n0=1.5
pathlenD(n,alpha,theta,A,B1)=pathlen(n,alpha,theta,A,Bmin(n0,alpha,theta,A,B1)) - \
   pathlen(n0,alpha,theta,A,Bmin(n0,alpha,theta,A,B1))

set nogrid
set xlabel 'Refractive index'
set ylabel 'Path length difference (mm)'
set key bottom right
set samples 200
set xra [1.5:1.7]
set xtics 0.05
set ytics 1


A=100
n0=1.6
alpha=10
theta=55
set term svg fsize 24


set outp 'prism_compressor_curve.svg'

plot pathlenD(x,alpha,theta,A,0) ti 'B = 67.6 mm', \
     pathlenD(x,alpha,theta,A,9) ti 'B = 76.6 mm', \
     pathlenD(x,alpha,theta,A,18) ti 'B = 85.6 mm'