196 lines
8.8 KiB
Python
196 lines
8.8 KiB
Python
import math
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import numpy as np
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import matplotlib.pyplot as plt
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from scipy.optimize import curve_fit
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from astropy import units as u, constants as ac
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def orderOfMagnitude(number):
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return math.floor(math.log(number, 10))
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def rotation_matrix(axis, theta):
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"""
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Return the rotation matrix associated with counterclockwise rotation about
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the given axis by theta radians.
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In 2-D it is just,
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thetaInRadians = np.radians(theta)
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c, s = np.cos(thetaInRadians), np.sin(thetaInRadians)
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R = np.array(((c, -s), (s, c)))
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In 3-D, one way to do it is use the Euler-Rodrigues Formula as is done here
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"""
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axis = np.asarray(axis)
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axis = axis / math.sqrt(np.dot(axis, axis))
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a = math.cos(theta / 2.0)
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b, c, d = -axis * math.sin(theta / 2.0)
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aa, bb, cc, dd = a * a, b * b, c * c, d * d
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bc, ad, ac, ab, bd, cd = b * c, a * d, a * c, a * b, b * d, c * d
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return np.array([[aa + bb - cc - dd, 2 * (bc + ad), 2 * (bd - ac)],
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[2 * (bc - ad), aa + cc - bb - dd, 2 * (cd + ab)],
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[2 * (bd + ac), 2 * (cd - ab), aa + dd - bb - cc]])
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# Rayleigh range
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def z_R(w_0:np.ndarray, lamb:float)->np.ndarray:
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return np.pi*w_0**2/lamb
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# Beam Radius
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def w(pos, w_0, lamb):
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return w_0*np.sqrt(1+(pos*lamb/(np.pi*w_0**2))**2)
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def trap_depth(w_1:"float|u.quantity.Quantity", w_2:"float|u.quantity.Quantity", P:"float|u.quantity.Quantity", alpha:float)->"float|u.quantity.Quantity":
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return 2*P/(np.pi*w_1*w_2) * (1 / (2 * ac.eps0 * ac.c)) * alpha * (4 * np.pi * ac.eps0 * ac.a0**3)
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def gravitational_potential(positions: "np.ndarray|u.quantity.Quantity", m:"float|u.quantity.Quantity"):
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return m * ac.g0 * positions
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def single_gaussian_beam_potential(positions: "np.ndarray|u.quantity.Quantity", waists: "np.ndarray|u.quantity.Quantity", alpha:"float|u.quantity.Quantity", P:"float|u.quantity.Quantity"=1, wavelength:"float|u.quantity.Quantity"=1.064*u.um)->np.ndarray:
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A = 2*P/(np.pi*w(positions[1,:], waists[0], wavelength)*w(positions[1,:], waists[1], wavelength))
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U_tilde = (1 / (2 * ac.eps0 * ac.c)) * alpha * (4 * np.pi * ac.eps0 * ac.a0**3)
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U = - U_tilde * A * np.exp(-2 * ((positions[0,:]/w(positions[1,:], waists[0], wavelength))**2 + (positions[2,:]/w(positions[1,:], waists[1], wavelength))**2))
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return U
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def single_gaussian_beam_potential_harmonic_approximation(positions: "np.ndarray|u.quantity.Quantity", waists: "np.ndarray|u.quantity.Quantity", depth:"float|u.quantity.Quantity"=1, wavelength:"float|u.quantity.Quantity"=1.064*u.um)->np.ndarray:
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U = - depth * (1 - (2 * (positions[0,:]/waists[0])**2) - (2 * (positions[2,:]/waists[1])**2) - (0.5 * positions[1,:]**2 * np.sum(np.reciprocal(z_R(waists, wavelength)))**2))
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return U
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def harmonic_potential(pos, v, offset):
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U_Harmonic = ((0.5 * 164*u.u * (2 * np.pi * v*u.Hz)**2 * (pos*u.um)**2)/ac.k_B).to(u.uK) + offset*u.uK
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return U_Harmonic.value
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def extractTrapFrequency(Positions, TrappingPotential, TrapDepthInKelvin, axis):
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tmp_pos = Positions[axis, :]
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center_idx = np.where(tmp_pos == 0)[0][0]
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lb = int(round(center_idx - len(tmp_pos)/20, 1))
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ub = int(round(center_idx + len(tmp_pos)/20, 1))
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xdata = tmp_pos[lb:ub]
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tmp_pot = TrappingPotential[axis]
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Potential = tmp_pot[lb:ub]
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p0=[1e3, -TrapDepthInKelvin.value]
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popt, pcov = curve_fit(harmonic_potential, xdata, Potential, p0)
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v = popt[0]
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dv = pcov[0][0]**0.5
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return v, dv, popt, pcov
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def plotHarmonicFit(Positions, TrappingPotential, TrapDepthInKelvin, axis, popt, pcov):
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v = popt[0]
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dv = pcov[0][0]**0.5
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happrox = harmonic_potential(Positions[axis, :].value, *popt)
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plt.figure()
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plt.plot(Positions[axis, :].value, happrox, '-r', label = '\u03BD = %.1f \u00B1 %.2f Hz'% tuple([v,dv]))
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plt.plot(Positions[axis, :], TrappingPotential[axis], 'ob', label = 'Gaussian Potential')
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plt.xlabel('Distance (um)', fontsize= 12, fontweight='bold')
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plt.ylabel('Trap Potential (uK)', fontsize= 12, fontweight='bold')
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plt.ylim([-TrapDepthInKelvin.value, max(TrappingPotential[axis].value)])
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plt.tight_layout()
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plt.grid(visible=1)
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plt.legend(prop={'size': 12, 'weight': 'bold'})
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plt.show()
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def plotPotential(Positions, Powers, ComputedPotentials, axis, TrapDepthLabels):
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## plot of the measured parameter vs. scan parameter
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plt.figure(figsize=(9, 7))
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for i in range(np.size(ComputedPotentials, 0)):
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v, dv, popt, pcov = extractTrapFrequency(Positions, ComputedPotentials[i], TrapDepthInKelvin, axis)
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unit = 'Hz'
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if v <= 0:
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v = np.nan
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dv = np.nan
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unit = 'Hz'
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elif v > 0 and orderOfMagnitude(v) > 2:
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v = v / 1e3 # in kHz
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dv = dv / 1e3 # in kHz
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unit = 'kHz'
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tf_label = '\u03BD = %.1f \u00B1 %.2f %s'% tuple([v,dv,unit])
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plt.plot(Positions[axis], ComputedPotentials[i][axis], label = 'P = ' + str(Powers[i]) + ' W; ' + TrapDepthLabels[i] + '; ' + tf_label)
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if axis == 0:
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dir = 'X'
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elif axis == 1:
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dir = 'Y'
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else:
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dir = 'Z'
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plt.xlabel(dir + ' Direction (um)', fontsize= 12, fontweight='bold')
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plt.ylabel('Trap Potential (uK)', fontsize= 12, fontweight='bold')
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plt.tight_layout()
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plt.grid(visible=1)
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plt.legend(prop={'size': 12, 'weight': 'bold'})
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plt.show()
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# plt.savefig('pot_' + dir + '.png')
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if __name__ == '__main__':
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# Powers = [0.1, 0.5, 2]
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# Powers = [5, 10, 20, 30, 40]
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Powers = [40]
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Polarizability = 184.4 # in a.u, most precise measured value of Dy polarizability
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w_x, w_z = 34*u.um, 27.5*u.um # Beam Waists in the x and y directions
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# w_x, w_z = 70*u.um, 70*u.um # Beam Waists in the x and y directions
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# w_x, w_z = 20.5*u.um, 20.5*u.um
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axis = 1 # axis referenced to the beam along which you want the dipole trap potential
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extent = 1e4 # range of spatial coordinates in one direction to calculate trap potential over
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TrappingPotential = []
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ComputedPotentials = []
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TrapDepthLabels = []
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gravity = True
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astigmatism = False
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tilt_gravity = True
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theta = 1 # in degrees
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tilt_axis = [1, 0, 0] # lab space coordinates are rotated about x-axis in reference frame of beam
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for p in Powers:
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Power = p*u.W # Single Beam Power
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TrapDepth = trap_depth(w_x, w_z, Power, alpha=Polarizability)
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TrapDepthInKelvin = (TrapDepth/ac.k_B).to(u.uK)
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TrapDepthLabels.append("Trap Depth = " + str(round(TrapDepthInKelvin.value, 2)) + " " + str(TrapDepthInKelvin.unit))
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projection_axis = np.array([0, 1, 0]) # default
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if axis == 0:
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projection_axis = np.array([1, 0, 0]) # radial direction (X-axis)
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elif axis == 1:
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projection_axis = np.array([0, 1, 0]) # propagation direction (Y-axis)
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elif axis == 2:
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projection_axis = np.array([0, 0, 1]) # vertical direction (Z-axis)
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x_Positions = np.arange(-extent, extent, 1)*u.um
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y_Positions = np.arange(-extent, extent, 1)*u.um
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z_Positions = np.arange(-extent, extent, 1)*u.um
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Positions = np.vstack((x_Positions, y_Positions, z_Positions)) * projection_axis[:, np.newaxis]
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if not gravity and not astigmatism:
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TrappingPotential = single_gaussian_beam_potential(Positions, np.asarray([w_x.value, w_z.value])*u.um, P = Power, alpha = Polarizability)
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TrappingPotential = TrappingPotential + np.zeros((3, len(TrappingPotential))) * TrappingPotential.unit
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TrappingPotential = (TrappingPotential/ac.k_B).to(u.uK)
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elif gravity and not astigmatism:
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# Influence of Gravity
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m = 164*u.u
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gravity_axis = np.array([0, 0, 1])
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if tilt_gravity:
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R = rotation_matrix(tilt_axis, np.radians(theta))
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gravity_axis = np.dot(R, gravity_axis)
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gravity_axis_positions = np.vstack((x_Positions, y_Positions, z_Positions)) * gravity_axis[:, np.newaxis]
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TrappingPotential = single_gaussian_beam_potential(Positions, np.asarray([w_x.value, w_z.value])*u.um, P = Power, alpha = Polarizability) + gravitational_potential(gravity_axis_positions, m)
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TrappingPotential = (TrappingPotential/ac.k_B).to(u.uK)
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elif not gravity and astigmatism:
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# Influence of Astigmatism
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pass
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else:
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# Influence of Gravity and Astigmatism
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pass
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# v, dv, popt, pcov = extractTrapFrequency(Positions, TrappingPotential, TrapDepthInKelvin, axis)
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# plotHarmonicFit(Positions, TrappingPotential, TrapDepthInKelvin, axis, popt, pcov)
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ComputedPotentials.append(TrappingPotential)
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ComputedPotentials = np.asarray(ComputedPotentials)
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plotPotential(Positions, Powers, ComputedPotentials, axis, TrapDepthLabels) |