Difference between revisions of "Light Polarization"

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=Description of the Experiment=
 
=Description of the Experiment=
This experiment allows to measure cross-polarization result of light. Two polarizers with variable angle are used in series over a white LED and the light intensity measured.
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This experiment allows you to polarize light from an incoherent source (a white LED) using a polarizer and study the effect caused by a second polarizer on the same beam of light, ultimately measuring the incident power on a photocell.
  
Light can be described as an electromagnetic wave with a property called polarization due to the electric field oscillation in the plane orthogonal to the propagation direction. When the oscillation is just over a single direction the light is said to be polarized. Certain materials have the property to block the wave except along this precise direction. The objective of this experiment is to reveal how this occur regarding the light intensity.
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Light can be described as an electromagnetic wave with a characteristic polarization, where its electric field oscillates in a specific plane perpendicular to the direction of its propagation. Certain media have the property of absorbing the wave in one direction on that plane and remaining "transparent" in the other direction, such as "Polaroid" lenses.
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<div class="toccolours mw-collapsible mw-collapsed" style="width:300px">
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The aim of this experiment is to demonstrate the effect of light passing through various polarizers by interposing them in the light optical path at various angles defined by the user. However, when there are a chain of three polarizers, we the interpretation of the effect of the polarizers can be quantum, especially when dealing with a single photon.
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<div class="toccolours mw-collapsible mw-collapsed" style="width:420px">
 
'''Links'''
 
'''Links'''
 
<div class="mw-collapsible-content">
 
<div class="mw-collapsible-content">
  
*Video: rtsp://elabmc.ist.utl.pt:554/polaroide.sdp
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*Laboratory: Intermediate [http://elab.tecnico.ulisboa.pt elab.tecnico.ulisboa.pt]
*Laboratory: Intermediate [http://e-lab.ist.eu e-lab.ist.eu]
 
 
*Control Room: Polaroide
 
*Control Room: Polaroide
 
*Grade: **
 
*Grade: **
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</div>
 
</div>
 
</div>
 
</div>
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==Who likes this idea==
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[[File:IYQST2025 IUPAP Logo.png|border|180px]]
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[[File:LogoSPF long.jpg|border|180px]]
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[[File:IUPAP_Logo.png|border|240px]]
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[[File:URSI_Logo.png|border|180px]]
  
  
 
=Experimental Apparatus=
 
=Experimental Apparatus=
The apparatus consists on a light source (high bright white LED) passing a collimator which focuses the light rays into a parallel beam of light. At the beginning of the optical path it can can be interposed a vertical light polariser.
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The apparatus consists on a light source (high bright white LED) passing a collimator, which focuses the light rays into a parallel beam of light. At the beginning of the optical path, a vertical light polariser can be interposed.
  
In the optical path light travel thought two polarized lenses without graduation whose angle of one of them is pre-set and the other is free to rotate around the axis of propagation.
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In the optical path, the light travels through two polarized lenses without graduation, having the angle of one of them been preset and being the other one free to rotate around the axis of propagation.
 
 
The light is finally collected through a converging lens into a photo-diode that measures the incident radiation intensity. This intensity is obviously the result of attenuation introduced by polarizing systems brought in its optical path.
 
  
 +
The light is finally collected through a converging lens into a photo-diode that measures the incident radiation intensity. This intensity is obviously the result of attenuation introduced by polarizing systems brought into its optical path.
  
 
=Protocol=
 
=Protocol=
In this control room we can measure the attenuation of a light beam caused by the cross-rotation of two polarises lenses. This beam can be selected from the light source or can be previously polarized.
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In this control room we can measure the attenuation of a light beam caused by the cross-rotation of two polarized lenses. This beam can be selected from the light source or can be previously polarized.
  
 
The supervisor of the experiment can choose two sweep limits for one polarizer and set the angle of the second polarizer acquiring the value of the transmitted power in a photo-diode.
 
The supervisor of the experiment can choose two sweep limits for one polarizer and set the angle of the second polarizer acquiring the value of the transmitted power in a photo-diode.
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The resolution (angle increment between two samples) can be chosen according to the interest of the control room supervisor.
 
The resolution (angle increment between two samples) can be chosen according to the interest of the control room supervisor.
  
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= Advanced protocol =
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The experience allows to be performed with starting with polarized light. Selecting this option the user can check the Malus's law in which multiple polarizers are used. In such case we need to multiply all the squares of the cosines between themselves, so the final value of the attenuation equation became:
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<math>
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I_s = I_a \prod cos ^ 2 (\alpha_i)
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</math>
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were \( \alpha_i \) are the successive polarizers angles and \(I_a\) the initial light intensity.
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In the case where two of the polarizers are at 90º between them, but the one between them is at an angle α, the sequential application of Malus' law leads to the following:
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 +
<math>
 +
I_s=I_a (cos (\alpha_i)cos(90-\alpha_i))^2=I_a (cos (\alpha_i)sen(\alpha_i))^2=\frac{I_a}{4}sen^2(2\alpha)
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</math>
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A paradox can arise from this, since if we have two polarizers at 90º no light will pass through, but by introducing a third polarizer between them at a proper angle such as 45º we already get light through the system, which will emerge attenuated (by 25% for 45º)!
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Nonetheless, the interpretation of this phenomenon of the "repolarization" of light <ref "3Polarizers>https://www.informationphilosopher.com/solutions/experiments/dirac_3-polarizers/ </ref>  necessarily has a [[Quantum interpretation of three polarizers | quantum interpretation ]] in the limit of a single photon. In this limit, the proposed experiment of the three consecutive polarizers can lead to a very interesting conclusion.
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=References=
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<references/>
  
 
=Links=
 
=Links=
 
*[[Polarização da Luz | Portuguese version (Versão em Português)]]
 
*[[Polarização da Luz | Portuguese version (Versão em Português)]]

Latest revision as of 14:21, 17 July 2024

Description of the Experiment

This experiment allows you to polarize light from an incoherent source (a white LED) using a polarizer and study the effect caused by a second polarizer on the same beam of light, ultimately measuring the incident power on a photocell.

Light can be described as an electromagnetic wave with a characteristic polarization, where its electric field oscillates in a specific plane perpendicular to the direction of its propagation. Certain media have the property of absorbing the wave in one direction on that plane and remaining "transparent" in the other direction, such as "Polaroid" lenses.

The aim of this experiment is to demonstrate the effect of light passing through various polarizers by interposing them in the light optical path at various angles defined by the user. However, when there are a chain of three polarizers, we the interpretation of the effect of the polarizers can be quantum, especially when dealing with a single photon.

Links

Who likes this idea

IYQST2025 IUPAP Logo.png LogoSPF long.jpg IUPAP Logo.png URSI Logo.png


Experimental Apparatus

The apparatus consists on a light source (high bright white LED) passing a collimator, which focuses the light rays into a parallel beam of light. At the beginning of the optical path, a vertical light polariser can be interposed.

In the optical path, the light travels through two polarized lenses without graduation, having the angle of one of them been preset and being the other one free to rotate around the axis of propagation.

The light is finally collected through a converging lens into a photo-diode that measures the incident radiation intensity. This intensity is obviously the result of attenuation introduced by polarizing systems brought into its optical path.

Protocol

In this control room we can measure the attenuation of a light beam caused by the cross-rotation of two polarized lenses. This beam can be selected from the light source or can be previously polarized.

The supervisor of the experiment can choose two sweep limits for one polarizer and set the angle of the second polarizer acquiring the value of the transmitted power in a photo-diode.

The resolution (angle increment between two samples) can be chosen according to the interest of the control room supervisor.

Advanced protocol

The experience allows to be performed with starting with polarized light. Selecting this option the user can check the Malus's law in which multiple polarizers are used. In such case we need to multiply all the squares of the cosines between themselves, so the final value of the attenuation equation became:

[math] I_s = I_a \prod cos ^ 2 (\alpha_i) [/math]

were \( \alpha_i \) are the successive polarizers angles and \(I_a\) the initial light intensity.

In the case where two of the polarizers are at 90º between them, but the one between them is at an angle α, the sequential application of Malus' law leads to the following:

[math] I_s=I_a (cos (\alpha_i)cos(90-\alpha_i))^2=I_a (cos (\alpha_i)sen(\alpha_i))^2=\frac{I_a}{4}sen^2(2\alpha) [/math]

A paradox can arise from this, since if we have two polarizers at 90º no light will pass through, but by introducing a third polarizer between them at a proper angle such as 45º we already get light through the system, which will emerge attenuated (by 25% for 45º)!

Nonetheless, the interpretation of this phenomenon of the "repolarization" of light [1] necessarily has a quantum interpretation in the limit of a single photon. In this limit, the proposed experiment of the three consecutive polarizers can lead to a very interesting conclusion.

References

Links