Physical Optics
The physical optics lab involves many different experiments: finding poisson's spot, measuring a lasers wavelength, building an interferometer, and working through a worksheet of physical optical problems.
Experiment 1: Finding Poisson's Spot
Poisson’s spot is a small bright point that appears at the very center of the shadow of a circular or spherical object when it is illuminated by beam of light, in our case from a green laser. ​
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When parallel light waves pass around the edges of a circular obstacle, they diffract and then interfere with each other in the region behind the object. At the exact center of the shadow, contributions from all points around the rim travel the same distance and arrive in phase, so they interfere constructively and produce a bright spot instead of darkness.
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Experiment 2: Measuring the Wavelength of a Laser
Experiment 3: Building an Interferometer
To set up a basic Michelson interferometer, we directed a laser beam onto a beamsplitter placed at about 45°. One part of the beam went straight to mirror 1 and the other part was reflected at a right angle to mirror 2. Both mirrors were positioned so that the reflected beams returned to the beamsplitter and recombined. For alignment and to get fringes, we adjusted the mirrors so the two returning beams overlap into a single spot on the screen. We then made fine tilts and small path‑length changes until we saw stable circular or straight interference fringes. This indicated that the interferometer arms are nearly equal and well aligned.
Result
Optics Experimental Review
What did we learn?
These three tasks allowed me to see that light behaves as a wave and that interference and diffraction are powerful tools for making precise measurements in physical optics. Seeing Poisson’s spot shows that light diffracts around obstacles and can interfere constructively even in the center of a shadow, measuring the wavelength of a laser allowed for practice calculating double slit interference, and building an interferometer developed understanding of optical path and phase.