Create Circularly Polarized Light Using a Quarter-Wave Plate (QWP) | Thorlabs Insights

Circularly polarized light can be generated by placing a quarter-wave plate in a linearly polarized beam, provided a couple of conditions are met. The first is that the light's wavelength falls within the wave plate's operating range. The second is that the wave plate's slow and fast axes, which are orthogonal, are oriented at 45° to the direction of the linear polarization state. When this is true, the incident light has equal-magnitude components parallel to the wave plate's two axes. The wave plate delays the component parallel to the slow axis by a quarter of the light's wavelength (pi/2) with respect to the component parallel to the fast axis. By creating this delay, the wave plate converts the polarization state from linear to circular.

An animation at the beginning of the demonstration illustrates the results of aligning the input linear polarization state with the wave plate's fast axis, slow axis, and angles in between. The perspective used to describe the angles and orientations is looking into the source, opposite the direction of light propagation. The procedure is then demonstrated for orienting input and output polarizers to define the reference orthogonal polarization directions, as well as provide polarization-dependent power measurements. The wave plate is placed between the two polarizers, and the effects of different orientations are explored. The quality of the circularly polarized light output by the wave plate is checked by rotating the second polarizer's transmission axis. The light's polarization is closer to circular when the power reading fluctuates less during rotation.

0:00 - Introduction
0:43 - QWP Use Discussed, Illustrated
3:24 - Step 1: Cross Linear Polarizers
5:19 - Step 2: Align QWP
8:40 - Step 3: Circular Polarization Check

Components used in this demonstration include:
- HeNe Laser: https://www.thorlabs.com/newgrouppage...
- HeNe Laser's Optical Isolator: https://www.thorlabs.com/newgrouppage...
- C1512 V-Clamp Mount: https://www.thorlabs.com/newgrouppage...
- PRM1 Precision Rotation Mounts: https://www.thorlabs.com/newgrouppage...
- BA2 Base: https://www.thorlabs.com/newgrouppage...
- WPQ10M-633 Zero-Order Quarter-Wave Plate: https://www.thorlabs.com/newgrouppage...
- LPVISC100-MP2 Linear Film Polarizers: https://www.thorlabs.com/newgrouppage...
- S130C Power Sensor: https://www.thorlabs.com/newgrouppage...
- SM1A29 SM1 Thread Adapter for the Power Sensor https://www.thorlabs.com/newgrouppage...
- SM1 Lens Tube: https://www.thorlabs.com/newgrouppage...
- PM400 Power Meter: https://www.thorlabs.com/newgrouppage...

For questions, please reach out to [email protected]; more photonics how-to videos can be found at https://www.thorlabs.com/newgrouppage....