What is the Difference Between Pockels Effect and Kerr Effect

The key difference between Pockels effect and Kerr effect is that in the Pockels effect, the birefringence is proportional to the electric field, whereas, in the Kerr effect, the change of the refractive index is proportional to the square of the field.

Pockels effect and Kerr effect are important physical concepts. These two effects are usually described according to their proportionality.

CONTENTS

1. Overview and Key Difference
2. What is Pockels Effect
3. What is Kerr Effect
4. Pockels Effect vs Kerr Effect in Tabular Form
5. Summary – Pockels Effect vs Kerr Effect 

What is Pockels Effect?

Pockels effect is the effect that can change or produce birefringence, which is an optical property of a material that is responsible for double refraction, in an optical medium that is induced by an electric field. In this effect, the birefringence is proportional to the electric field. This effect was named after Friedrich Carl Alwin Pockels in 1893.

Typically, the Pockels effect takes place only in crystals that lack inversion symmetry. Some examples include monopotassium phosphate, deuterated potassium dihydrogen phosphate, lithium niobate, etc.

A Pockels cell is a voltage-controlled wave plate. These cells are built on the basis of the Pockels effect. These cells can be used in rotating the polarization of a beam that can pass through. Usually, a transverse Pockels cell contains two crystals in the opposite orientation. These two together give a zero-order wave plate upon the turning off of voltage. Often, this is not perfect, and it tends to drift with temperature.

Pockels cells are used in various scientific and technical applications. We can use a Pockels cell in combination with a polarizer to switch between no optical rotation and 90-degree rotation. This creates a fast shutter that is able to open and close in nanoseconds.

What is Kerr Effect?

The Kerr effect is the inducement of double refraction of light in a transparent substance when a strong electric field is applied in a direction that is transverse to the beam of light. This effect has been known for some time. It is also known as a quadratic electro-optic effect. Generally, all materials show the Kerr effect. However, certain liquids tend to display it more strongly compared to others. This effect was introduced in 1875 by John Kerr, a Scottish physicist.

There are two specific cases regarding the Kerr effect: Kerr electro-optic effect or DC Kerr effect and optical Kerr effect or AC Kerr effect. The former is a special case that involves the application of a slowly varying external electric field, such as a voltage on electrodes, across the analyte material, which can make the sample analyte birefringent. The latter is the special case in which the electric field occurs due to the light itself, which can cause the variation in the index of refraction that is proportional to the local irradiance of the light.

What is the Difference Between Pockels Effect and Kerr Effect?

Pockels effect and Kerr effect are important chemical concepts. The key difference between Pockels effect and Kerr effect is that in the Pockels effect, the birefringence is proportional to the electric field, whereas, in the Kerr effect, the change of the refractive index is proportional to the square of the field. Moreover, compared to the Kerr effect, the Pockels effect is quite strong due to the proportionality to the electric field.

Below is a summary of the difference between Pockels effect and Kerr effect in tabular form for side-by-side comparison.

Summary – Pockels Effect vs Kerr Effect

Pockels effect is the effect that can change or produce birefringence in an optical medium that is induced by an electric field while the Kerr effect is the inducement of double refraction of light in a transparent substance when a strong electric field is applied in a direction that is transverse to the beam of light. The key difference between Pockels effect and Kerr effect is that in the Pockels effect, the birefringence is proportional to the electric field, whereas, in the Kerr effect, the change of the refractive index is proportional to the square of the field.

Reference:

1. “Kerr Effect.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Pockels cell modulaliing light polarization” By Ben Smith – Own work (CC BY-SA 4.0) via Commons Wikimedia