#!/usr/bin/env python
# -*- coding: utf8 -*-

'''
Copyright (C) 2015 Geek3, Wikimedia Foundation

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
'''

from math import *
import scipy
from PIL import Image

w = 600
h = 300
image = scipy.zeros((h, w))


lambda_px = 24.
w0 = 24.

def E(r, z, w0):
    z0 = pi * w0**2 / lambda_px
    w = w0 * sqrt(1. + (z / z0)**2)
    k = 2. * pi / lambda_px
    R = z * (1. + (z0 / z)**2)
    gouy = atan(z / z0)
    E = w0 / w
    E *= e ** (-(r/w)**2)
    E *= e ** (-1j * k * r**2 / (2 * R))
    E *= e ** (1j * (gouy - k * z))
    return E


for y in range(h):
    for x in range(w):
        z = (x + 0.5) - w / 2.0
        r = -(y + 0.5) + h / 2.0
        EE = E(r, z, w0)
        image[y, x] = 0.5 * abs(EE) + 0.5 * EE.imag


# write image to file
image_file = Image.new('L', (w, h))
for y in range(h):
    for x in range(w):
        c = int(2**8 * image[y, x])
        image_file.putpixel((x, y), c)
image_file.save('gaussianbeam_fieldamplitude_wb.png', 'PNG')