Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization  Measuring light transmission through a dichroic material (“polarizer sheet”) as a function of polarization angle to verify Malus’ Law  Using polarization by reflection to determine the Brewster angle and then calculate the index of refraction of the reflecting material.  Qualitative observation of light polarization by scattering. Topics

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Linearly polarized light

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Dichroic Absorption PassesIs absorbed Partially absorbed and partially passes

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Dichroic Absorption Partially absorbed and partially passes (Malus’ Law)

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Polarization Dependent Reflection Incident plane: Plane that contains incident, reflected and transmitted ray.

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Polarization Dependent Reflection Incident plane: Plane that contains incident, reflected and transmitted ray. “Parallel polarized” light. (parallel to incident plane) “p-polarized” (p as in “parallel”)

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Polarization Dependent Reflection Incident plane: Plane that contains incident, reflected and transmitted ray. “Perpendicular polarized” light. (perpendicular to incident plane) “s-polarized” (s as in “senkrecht”)

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Fresnel Equations Reflection Coefficients: Reflection coefficients (relate to Electric field strength ratios) For parallel polarized light: For perpendicular polarized light:

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Reflectances (relate to intensity ratios):

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Brewster angle: R || =0

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Brewster Angle “Parallel polarized” light is not reflected at all if incident under the “Brewster Angle”

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Reflected light is s-polarized under the Brewster angle.

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Radiation pattern from an accelerated charge e- Radiation is polarized

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Radiation pattern from an accelerated charge e- Length of arrow indicates intensity in that direction

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Scattered light e- incoming light nothing scattered in this direction scattered light nothing scattered in this direction

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Scattered light e- incoming light nothing scattered in this direction scattered light nothing scattered in this direction

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Scattered light incoming light- unpolarized scattered light polarized e- polarized

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Rayleigh Scattering incoming light

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Intensity of scattered light incoming light- unpolarized e-

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Color of scattered light incoming light assume equal color intensity Unscattered light Scattered light Looking at sunset Looking at sky above

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization Experimental Details: Using the Photometer to Measure Intensity Zero Adjust VariableSensitivity Probe Input CAL. “Zero” adjustment:  Start with “Sensitivity” 1000 (least Sensitive)  Close off “Probe Input” with rubber stopper so that no light enters.  Use Zero Adjust button to get needle to zero.  Go to more sensitive setting (lower number) and zero, etc. Measurement of Intensity:  Start with “Sensitivity” 1000 (least Sensitive)  Plug fiber optic cable into “Probe Input”.  Step by step increase sensitivity but make sure needle stays within range. See pages 19 ff of the “Advanced Optics Manual” for detailed operating instructions!!

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.A Dichroic Absorption Is the laser polarized? Laser Polarizer Screen

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.A Measuring I(  ) and verifying Malus’ Law  Zero Photometer  Attach fiber optic cable to photometer and to rotational stage (tighten screw only very lightly otherwise fiber optic cable may break internally). Do not bend fiber optic cable too tightly. Top view Laser Fiber Optic Cable Photometer Polarizer  Measure I(  ).  Plot I(  ) versus cos 2 .

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.A Measuring I(  ) with two polarizers Laser Polarizer 1 Screen Polarizer 2  Vary the orientation   of polarizer 1.  Measure I(   ) plot versus  .  Explain results.

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.B Orienting the laser polarization to be horizontal  Rotate laser so that E-vector is horizontal (from V.A. you should know approximate orientation already).  With polarizer oriented as shown, fine tune the laser orientation until light transmission is minimized. Top view Laser Polarizer (0-180 direction vertical) Screen

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.B Adjusting the glass plate  Front surface of glass plate should be hit by laser exactly at the rotation axis of the rotation stage.  Calibrate the zero degree position by using the back-reflection of the laser. Top view Laser Glass plate Short component holder Polarizer (0-180 direction vertical)

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.B Finding the Brewster angle  Rotate until reflection intensity is minimized to find the Brewster angle.  Calculate the index of refraction of glass from the Brewster angle. Top view Laser Polarizer (0-180 direction vertical) Screen

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.B Adjusting the glass plate  Front surface of glass plate should be hit by laser exactly at the rotation axis of the rotation stage.  Adjust 127mm lens so that sharp image of filament is seen on back side of lens holder.  Adjust glass plate orientation so that filament image is in the middle of lens holder. Top view Glass plate Short component holder Incandescent Light 200mm 127mm lens Approx.330mm Filament image Approx.750mm

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.B Adjusting lens position and getting Brewster angle  Rotate rotational stage by approx. 30 degrees.  Readjust lens position so that filament is in focus on the screen.  With polarizer select parallel polarization component. Look at intensity versus incident angle. Then do the same for perpendicular polarization component.  Make a qualitative comparison of I(  ) for the two components.  Determine the Brewster angle again. Top view Incandescent Light Screen Polarizer 127mm lens

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.C Polarization by Scattering  Front surface of glass plate should be hit by laser exactly at the rotation axis of the rotation stage.  Adjust 127mm lens so that sharp image of filament is seen on back side of lens holder.  Adjust glass plate orientation so that filament image is in the middle of lens holder. Top view Screen Murky water Incandescent Light 48mm lens Approx. 4cm Look from side (and look from top) through polarizer

Modern Optics Lab Lab 5 Part 1: Experiments involving Light Polarization V.C Scattering of polarized laser light  Look from side (and then from top down).  Observe scattered light intensity as you rotate the laser’s polarization. Top view Screen Murky water Laser Look from side (and look from top) through polarizer