What is the Difference Between Dichroism and Birefringence

The key difference between dichroism and birefringence is that dichroism induces the polarization selective attenuation of the medium, whereas birefringence retards one of the light field components having orthogonal polarization.

There are two elementary types of polarization properties in anisotropic media. These are known as dichroism and birefringence.

CONTENTS

1. Overview and Key Difference
2. What is Dichroism  
3. What is Birefringence
4. Dichroism vs Birefringence in Tabular Form
5. Summary – Dichroism vs Birefringence

What is Dichroism?

Dichroism is a term used in optics to describe the property of particular materials displaying the ability to absorb light that is vibrating in a certain plane and is comparatively stronger than the light that is vibrating in an orthogonal plane. We can observe dichroism upon the absorption band intensity that changes when the relative orientation of the polarizer tends to alter. In other words, this is the phenomenon in which light absorption alters in different directions of polarization.

The most common form of dichroism is circular dichroism or CD. It refers to the absorption of two kinds of circularly polarized light. For example, DNA molecules have a chiral sugar present in their structure which makes them have an intrinsic asymmetry. This gives a strong interaction ability between the chromophore bases. Therefore, it generates an intense circular dichroism spectrum.

Generally, there are two types of definitions for dichroism. In beam splitters, dichroism means the splitting of a beam of light into two beams having different wavelengths, whereas, in the context of polarized light, it refers to the traveling of different polarization states through a medium where it experiences different absorption coefficients (named as diattenuation).

What is Birefringence?

Birefringence is the double refraction of light in a material that is transparent and is manifested by the existence of differences that are orientation-dependent with respect to the refractive index. In other words, it is a phenomenon in which the incident light can be divided into two components. Therefore, upon transmission of the light observed through the optically anisotropic sample, we can detect the two components using the difference phase (which is the main parameter of birefringence imaging).

This phenomenon is responsible for double refraction in which a ray of light is split into two rays by polarization upon the light ray incident on a birefringence material. This gives slightly different paths for the new two light rays. This phenomenon was first discovered by the Danish scientist Rasmus Bartholin in 1669.

What is the Difference Between Dichroism and Birefringence?

The terms dichroism and birefringence are important in the optical mechanics of different materials. The key difference between dichroism and birefringence is that dichroism induces the polarization selective attenuation of the medium, whereas birefringence retards one of the light field components having orthogonal polarization.

The following table summarizes the difference between dichroism and birefringence.

Summary – Dichroism vs Birefringence

Dichroism is the ability of a particular substance to absorb light that is vibrating in a certain plane and is comparatively stronger than the light that is vibrating in an orthogonal plane. Birefringence, on the other hand, is the double refraction of light in a material that is transparent and is manifested by the existence of differences that are orientation-dependent with respect to the refractive index. The key difference between dichroism and birefringence is that dichroism induces the polarization selective attenuation of the medium, whereas birefringence retards one of the light field components having orthogonal polarization.

Reference:

1. “Dichroism.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Dichroicclose” By User:Pschemp – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Positively birefringent material” By Mikael Häggström – Own work (Public Domain) via Commons Wikimedia