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How Light’s Incident Angle Affects Transmission & Finding Brewster’s Angle | Thorlabs Insights

It is common to assume 4% of light reflects from a glass surface. While this rule-of-thumb can be used near normal incidence, the approximation is not appropriate for all incident angles, and it does not provide information about the input polarization state's effect on the reflected and transmitted optical powers. During this demonstration, light reflected from, and transmitted through, a rotating glass window is observed and compared with the results from Fresnel equation modeling. The limits of the 4% rule are investigated, and the polarization dependence of the reflectance and transmittance values are explored. First S-polarized and then P-polarized input light is incident upon the rotating window, which reveals that the light’s reflectance and transmittance values depend on the input polarization state of the incident beam. (S-polarized light is linearly polarized perpendicular to the plane of incidence and P-polarized light is linearly polarized parallel.) It is shown that there is an angle of incidence at which all incident P-polarized light is transmitted, so that only S-polarized light is reflected. This is called the Brewster’s angle, and an approach is demonstrated to orient the window so that the light is incident at Brewster’s angle. Linearly polarized input light oriented at 45° to the plane of incidence is also used to demonstrate that, when transmittance and reflectance values for pure S- and P-polarized light are known, it is possible to use these values to predict the values for unpolarized light. 00:00 Introduction 00:34 Fresnel Equations & Polarization 02:33 Stable, Linearly Polarized Input 03:21 S-Polarized Input 04:14 P-Polarized Input 05:05 45° Linear Polarized Input 06:28 Brewster’s Angle Components used in this Demonstration Include: - HRS015 Stabilized HeNe Laser: https://www.thorlabs.com/thorproduct.... - C1513 V-Clamp Mount: https://www.thorlabs.com/newgrouppage... - PM4 Clamping Arm: https://www.thorlabs.com/newgrouppage... - DP8A Damped Post, Ø1.5” Posts: https://www.thorlabs.com/newgrouppage... - C1498 Post Clamp, Ø1.5” Posts: https://www.thorlabs.com/newgrouppage... - WW41050 UVFS Wedged Window: https://www.thorlabs.com/newgrouppage... - FMP1 Fixed Mirror Mount: https://www.thorlabs.com/newgrouppage... - KB1X1 Kinematic Base: https://www.thorlabs.com/newgrouppage... - RS2P8 Pillar Post: https://www.thorlabs.com/newgrouppage... - RSHT1.5 Post Holder with Flexure Lock: https://www.thorlabs.com/newgrouppage... - PRM1SP1 Adapter Plate: https://www.thorlabs.com/newgrouppage... - PRM1Z8 Motorized Rotation Mount: https://www.thorlabs.com/newgrouppage... - KDC101 K-Cube Motor Controller: https://www.thorlabs.com/newgrouppage... - KPS201 Power Supply: https://www.thorlabs.com/newgrouppage... - WPQ05M-633 Pseudo-True Zero-Order Quarter-Wave Plate: https://www.thorlabs.com/newgrouppage... - PRM1 Mount: https://www.thorlabs.com/newgrouppage... - Linear Polarizer: https://www.thorlabs.com/navigation.c... - RSP1X225 Indexed Rotation Mount: https://www.thorlabs.com/newgrouppage... - Laser Line Filter: https://www.thorlabs.com/newgrouppage... - PM400 Power Meter: https://www.thorlabs.com/newgrouppage... - S130C Power Sensor: https://www.thorlabs.com/newgrouppage... - SM1A29 Thread Adapter for Power Sensor: https://www.thorlabs.com/newgrouppage... - SM1D12D Iris: https://www.thorlabs.com/newgrouppage... - Lens Tubes: https://www.thorlabs.com/newgrouppage... - SM1T1 Lens Tube Coupler: https://www.thorlabs.com/newgrouppage... - DTSM1 SM1-Thread-to-Dovetail Adapter: https://www.thorlabs.com/newgrouppage... - DT108 Dovetail Adapter: https://www.thorlabs.com/newgrouppage... - EDU-VS2 Viewing Screen: https://www.thorlabs.com/newgrouppage... - R2, Post Collar: https://www.thorlabs.com/newgrouppage... For more photonics how-to videos, visit https://www.thorlabs.com/newgrouppage...