Polarization of Light Using The Polarimeter

Content of this page :

1.    Introduction of the experiment.

2.    Aim of the experiment.

3.    Tools of the experiment.

4.  Steps and methods of the experiment.

5.   Parameter of the experiment.

6.    Medical application and advantages of the experiment.

1. Introduction of the experiment:

Light, like all other electromagnetic radiation, is characterized by propagation in vacuum with electric and magnetic field s which at each point in space are perpendicular to the direction of propagation and to each other.

If in addition each field lies always parallel to a single plane, the wave is said to be plane-polarized.

2. Aim of the experiment:

The aim of polarizing light using a polarimeter is primarily to study and analyze the polarization properties of light. Polarization refers to the orientation of the electric field vector of light waves as they propagate.

3-Tools of The experiment

  • Polarizer.
  • Analyzer.
  • Light Source.
  • Sample Holder.
  • Rotatable Mounts.
  • Detector.
  • Computer Interface (Optional).
  • Optical Components.

4. Steps and methods of the experiment:

To measure optical activity, we use a polarimeter in which light of wavelength 589.9 nm (Sodium-D line) is first plane-polarized by a polarizer, and then studied by a second polarizer to find its new plane of polarization after passing through the sample substance.
In order to increase the accuracy of measurement, in one half of the field of view, there is a Laurent’s quartz plate, which rotates the plane of polarization through a further small angle. The analyzer is now set to equal brightness on the two sides of the field of view, this gives a sharp setting and is easy to reproduce (Weber – Fechner Law).
Prepare a sugar solution of a known concentration (C). The rotation of this solution is determined in the half-shade polarimeter, by adjusting the two halves of the field to identical brightness.
Plot a graph of the rotation as a function of the concentration (C), and determine the value of the specific rotation from the graph.
Notice that:
The temperature of the solutions should be the same in all cases.

5. Parameter of The Experiment:

Optical activity is the ability of many substances to rotate the plane of vibration of a ray of plane-polarized light passing through them. It is caused by the two components of a plane-polarized ray of light traveling at different speed through the asymmetric medium, and in so doing, undergoing a phase shift with respect to one another, this phase shift being indicated as a rotation of the plane of polarization.
The specific rotation (rotary power) of solutions of optically active substance is defined as: the angle through which the plane of polarization of a ray of Sodium-D light (wavelength λ = 589.3 nm), would be rotated by a column of solution (100mm) in length, containing (1 g) of substance per (cm3), at (20°C). 

it is expressed by the symbol:

If we assume that the rotation is proportional to the concentration (C), then the specific rotation can be determined from the rotation (a) at a known concentration (C).

(Related to a column length of 100 mm)
If the measurement temperature departs from (20°C), the value
obtained must be corrected in accordance with:

6. Medical application

  • Polarized Light Microscopy:

    • Dermatology: Polarized light microscopy is used to examine skin tissue samples. It enhances the contrast and visibility of structures like collagen fibers, which appear birefringent under polarized light. This helps dermatologists in diagnosing skin diseases and conditions such as dermatitis, scleroderma, and connective tissue disorders.
  • Eye Care:

    • Corneal Imaging: Polarized light techniques are employed in ophthalmology for examining the cornea. The corneal collagen fibers exhibit birefringence, and polarized light can reveal structural details that aid in assessing corneal health and detecting abnormalities such as keratoconus.
  • Histopathology:

    • Tissue Analysis: Polarization microscopy is utilized in histopathology to study tissue sections stained with polarizing dyes or naturally birefringent tissues (e.g., muscle fibers). It helps pathologists visualize tissue structure and identify abnormalities in diseases such as cancer and fibrosis.
  • Polarized Light Imaging in Surgery:

    • Surgical Navigation: During neurosurgery and other delicate procedures, polarized light imaging techniques can assist surgeons in distinguishing between healthy and diseased tissues based on their polarization properties. This aids in precise tissue resection and minimizes damage to surrounding healthy tissue.
  • Dental Applications:

    • Dental Imaging: Polarized light is used in dentistry to analyze the composition and condition of dental tissues such as enamel and dentin. It helps in diagnosing dental caries, assessing tooth wear, and evaluating the effectiveness of dental treatments.
  • Biomedical Research:

    • Cell and Tissue Studies: Researchers use polarized light techniques to investigate the structural and optical properties of cells and tissues in vitro. This includes studying cell morphology, alignment of collagen fibers in engineered tissues, and the effects of treatments on tissue birefringence.
  • Medical Imaging Devices:

    • Optical Coherence Tomography (OCT): Polarization-sensitive OCT utilizes polarized light to enhance contrast and depth resolution in imaging biological tissues, particularly in ophthalmology for retinal imaging and in cardiovascular medicine for vessel wall assessment.

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