How Light's Polarization Can Change After Reflecting from a Metal Mirror | Thorlabs Insights

Описание: Metallic mirrors are frequently used to steer light through optical setups. The beam’s direction and shape are typically monitored and optimized after mirror reflection, but reflection-induced changes to the beam’s polarization state are often not considered. Disregarding these changes is reasonable if the application is not polarization-dependent, but it can lead to unexpected results if the application is sensitive to polarization.

Reflection from a metallic surface can change light’s polarization state because metals have complex refractive indices, which are different for P- and S-polarized light. When light is purely S- or P-polarized, incident and reflected polarization states are the same. However, linearly polarized light that is a combination of S- and P-polarized light will usually be reflected as elliptically polarized light. A further complication to consider is that the polarization state of the incident light can be changed by just tilting the mirror, since the polarization state is based on the plane of incidence.

In this demonstration, we explore these concepts and show what to expect when different linear polarization states reflect from a protected silver mirror oriented at a 45° angle. The polarization state of the incident light is determined using measurements taken with a polarimeter constructed from a quarter-wave plate, linear polarizer, and power sensor. Our Stokes parameter calculations take into account the wave plate’s actual retardance, which improves accuracy. The polarization state of the reflected light is measured using a turnkey polarimeter, whose polarization ellipse display is used to visualize the dynamic polarization changes that occur as the incident linear polarization state rotates between S- and P-polarized light.

00:00 Introduction
01:13 Polarization After Reflection
03:31 Input Beam Setup Overview
04:14 DIY Polarimeter Overview
04:52 Measure QWP Retardance
7:15 Measure Stokes Parameters
8:25 Reflection of P-Polarized Input
9:34 Reflection of S-Polarized Input
11:04 Other Linearly Polarized Inputs

Components used in this demonstration include:
HRS015B Stabilized HeNe Laser: https://www.thorlabs.com/newgrouppage...
C1513 V-Clamp Post Mount, Kinematic: https://www.thorlabs.com/newgrouppage...
PM4 Clamping Arm: https://www.thorlabs.com/newgrouppage...
Posts, Ø1.5”: https://www.thorlabs.com/newgrouppage...
PB2 Post Base: https://www.thorlabs.com/newgrouppage...
SM1B2 Isolator-to-SM1 Adapter: https://www.thorlabs.com/newgrouppage...
IO-3D-633-VLP Optical Isolator, 633 nm: https://www.thorlabs.com/newgrouppage...
RSP1C Rotation Mount: https://www.thorlabs.com/newgrouppage...
WPQSM05-633 Quarter-Wave Plate, Pseudo-Zero-Order, 633 nm: https://www.thorlabs.com/newgrouppage...
SM1A6 Threading Adapter, SM1-to-SM05: https://www.thorlabs.com/newgrouppage...
RSP1X225 Rotation Mount, Indexed or Continuous Rotation: https://www.thorlabs.com/newgrouppage...
LPVISC100-MP2 Mounted Linear Polarizer: https://www.thorlabs.com/newgrouppage...
PF10-03-P01 Silver Mirror: https://www.thorlabs.com/newgrouppage...
NX1N Optics Mount, 16 Indexed Positions: https://www.thorlabs.com/newgrouppage...
WPMQ05M-633 Quarter-Wave Plate, Multi-Order, 633 nm: https://www.thorlabs.com/newgrouppage...
S130C Power Sensor: https://www.thorlabs.com/newgrouppage...
PM400 Power Meter: https://www.thorlabs.com/newgrouppage...
SMR1 Mount, SM1 Threads: https://www.thorlabs.com/newgrouppage...
Lens Tubes, Ø1”: https://www.thorlabs.com/newgrouppage...
PAX1000VIS Polarimeter: https://www.thorlabs.com/newgrouppage...
KM200PM Kinematic Prism Mount: https://www.thorlabs.com/newgrouppage...
MSB46 Optical Breadboard, Mini-Series: https://www.thorlabs.com/newgrouppage...
R2 and R2T Post Collars: https://www.thorlabs.com/newgrouppage...

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