PASCO OS-8170A Brewster’s Angle Accessory - Manual (Page 10)

Brewster’s Angle Accessory Model No. OS-8170A
10
®®
8. The square Analyzing Polarizer (see Figure
9) has its transmission axis marked.
Position the Analyzing Polarizer with its
label on top and with its axis horizontal.
NOTE: When the Analyzing Polarizer is
horizontal, the light passing through the
polarizer is the horizontal component
(perpendicular to the “D” lens surface) of the
light reflected from the flat surface of the “D”
lens. In this orientation, the Analyzing
Polarizer is blocking the light that is polarized
parallel to the flat surface of the “D” lens. Thus, when the incident angle is such that the
reflected light is 100% polarized parallel to the flat surface of the “D” lens (Brewster’s Angle),
the horizontal component will be zero.
During the experiment, both the horizontal and vertical components of the reflected light are
measured so the horizontal component of interest can be normalized by dividing by the sum of
the two components. This gives a percentage of the total reflected light that is horizontally
(perpendicularly) polarized.
Each measurement must also be divided by the reference light intensity to account for
momentary changes in intensity of the laser light source.
NOTE: The laser light is already polarized, but the round polarizer set at 45° solves the
problem. To make the relative intensities of the “p” (parallel) and “s” (perpendicular)
components the same, the light is polarized at 45°.
Sensor Setup
1. Connect the PASCO interface to the computer and start the data acquisition software.
2. If you are using DataStudio, open the DataStudio setup file titled “Brewsters_PASPORT.ds”
(for PASPORT) or “Brewsters.ds” (for ScienceWorkshop).
3. Plug the Rotary Motion Sensor and the two High Sensitivity Light Sensors into the interface.
Set the Light Sensor Range
1. To get full use of the Light Sensor range, set the light sensor range: for a PASPORT sensor,
press the “light bulb” button on the side of the sensor and for a ScienceWorkshop sensor, set
the “GAIN” switch on the top of the sensor to 100.
2. In the data acquisition program, click “Start” and rotate the first round polarizer (nearest to
the laser) to allow the light level to be as high as possible without exceeding 95% on the
Digits display of the Reflected Light Intensity (measured by the sensor on the
Spectrophotometer Arm) and the Reference Light Intensity (measured by the sensor on the
second optics bench). Click “Stop”.
Analyzing Polarizer
“D” Lens
“D” Lens
Mount Pivot
Plate
Spectrophotometer Degree Plate
Spectrophotometer Arm
Figure 9: Analyzing Polarizer and “D” Lens
Aperture Bracket
Light
Sensor