Build a Polarimeter to Find Stokes Values, Polarization State (Viewer Inspired) | Thorlabs Insights

A polarimeter, which is an optical tool used to measure the polarization state of light, can be constructed using linear polarizers, a quarter-wave plate, and an optical power sensor and meter. This video describes two methods for building a manual polarimeter, the classical method and the rotating wave plate method, and then uses both to measure a laser beam's polarization state. [1] Both approaches provide measurement data that describe the polarization state in terms of the four Stokes parameters. This demonstration includes discussion of the relationships between the Stokes parameters and different polarization states, including linearly and circularly polarized light.

In this demonstration, polarization handedness is defined with respect to time and from a perspective of looking into the beam, back towards the source. This video illustrates this convention by visualizing a fixed viewing plane oriented perpendicular to the propagating beam. As the beam passes through the plane, the beam's instantaneous polarization vector traces out a shape on the plane. The shape is traced out as a function of time, and the direction in which the shape is traced corresponds to the handedness of the light. The shape itself is the polarization ellipse, which is a convenient and common way to describe light's polarization state. The relationship between the polarization ellipse and the Stokes parameters is also discussed.

Prior to filming, the transmission axes of the linear polarizers and wave plate used to build these polarimeters were oriented with respect to the table. The following are links to Video Insights demonstrating the described alignment procedures:

- Align a linear polarizer horizonal or vertical with respect to the table:    • Align a Linear Polarizer's Axis to be...  
- Align a linear polarizer at 45° with respect to the table:    • Align a Linear Polarizer 45° to the P...  
- Align a wave plate's axis to be horizontal with respect to the table:    • Create Circularly Polarized Light Usi...  
- Determine whether a wave plate's axis is fast or slow:    • Distinguish the Fast and Slow Axes of...  

[1] Beth Schaefer, Edward Collett, Robert Smyth, Daniel Barrett, and Beth Fraher "Measuring the Stokes polarization parameters," Am. J. Phys. 75, 163-168 (2007).

00:00 - Introduction
00:42 - Stokes Parameters
02:55- Polarization State and Handedness
03:26 -Polarization Ellipse
03:53 - Classical Stokes Parameter Measurement
08:55 - Rotating Quarter Wave-Plate Method

Components used in this demonstration include:
- HeNe Lasers: https://www.thorlabs.com/navigation.c...
- Optical Isolator: https://www.thorlabs.com/newgrouppage...
- Linear Polarizers: https://www.thorlabs.com/navigation.c...
- PRM1 Rotation Mount: https://www.thorlabs.com/newgrouppage...
- Wave Plates: https://www.thorlabs.com/navigation.c...
- WPMQ05M-633 Quarter-Wave Plate: https://www.thorlabs.com/newgrouppage...
- RSPC Fixed Position Retainer: https://www.thorlabs.com/newgrouppage...
- SM1D12D Iris: https://www.thorlabs.com/newgrouppage...
- SM1L20 Lens Tube: https://www.thorlabs.com/newgrouppage...
- SM1QA Quick-Release Lens Tube Adapter: https://www.thorlabs.com/newgrouppage...
- S130C Power Sensor: https://www.thorlabs.com/newgrouppage...
- PM400 Power Meter: https://www.thorlabs.com/newgrouppage...

For more photonics how-to videos, visit https://www.thorlabs.com/newgrouppage...