6C10.15 - Diffraction - Laser and Adjustable Slit | Instructional Resources and Lecture Demonstrations - Department of Physics & Astronomy

Code Number: 6C10.15

Demo Title: Diffraction - Laser and Adjustable Slit

Condition: Good

Principle: Diffraction of Waves

Area of Study: Optics, Astronomy

Equipment:

Helium-Neon Laser (2 to 5 mW), Optics Bench, and Single Slit (Adjustable).

Procedure:

Put the adjustable slit in the path of the laser beam. As you adjust the slit width observe the changing diffraction patterns.

Another variation of the previous single slit demo is to partially submerge the variable slit in a tank of water. Measurable differences between the pattern produced through the air as opposed to through the water can be observed and used for calculations.

There are also a variety of other demos and resources that are used for Quantum Uncertainty Principle. They are:

#1 - (According to Gemini AI) - Variable single slit diffraction. Explanation:

The Setup: Shine a laser pointer through a very narrow vertical variable slit.
The Action: Slowly make the slit narrower.
The Result: Intuitively, you’d expect the dot on the wall to get smaller. Instead, once the slit gets thin enough, the light starts spreading out horizontally.
The Why: Due to Heisenberg's Uncertainty Principle ( $ΔyΔpy≥ℏ2\Delta y \Delta p_y \ge \frac{\hbar}{2}$ $Δ$ $y$ $Δ$ $p$ $y$ $$ $\geq$ $2$ $ℏ$ $$ ), a decrease in $Δy\Delta y$ $Δ$ $y$ necessitates an increase in $Δpy\Delta p_y$ $Δ$ $p$ $y$ $$ . This means the particle acquires a range of possible momenta in the y-direction. By narrowing the slit, you are "squeezing" the photon's position (smaller Delta y). To satisfy the uncertainty principle, the momentum (larger Delta p_y) must increase. This extra momentum manifests as the light "kicking" out to the sides, creating a wide diffraction pattern.
See 6H30.10 or 7A55.20 for more Uncertainty Demos.

References:

Christopher L. Panuski and Carl E. Mungan, "Single-Slit Diffraction: Transitioning from Geometric Optics to the Fraunhofer Regime", TPT, Vol. 54, #6, Sept. 2016, p. 356.
Samuel Hirchman and Eugene Hecht, "What Happens if w< l?", TPT, Vol. 19, #6, Sept. 1981, p. 427.
Samuel Hirschman, "Diffraction of Light Apparatus", TPT, Vol. 14, #3, Mar. 1976, p. 180, also A Potpourri of Physics Teaching Ideas - Optics and Waves, p. 233.
Mario Iona, "Comments About Slit Diffraction", TPT, Vol. 10, #6, Sept. 1972, p. 323.
"O-505. Fixed, Variable & Finger Slit", DICK and RAE Physics Demo Notebook, 1993.
G. D. Freier and F. J. Anderson, "Ol-7", A Demonstration Handbook for Physics.
Robert Ehrlich, "Q.10. Variable-Width Slit Using Razor Blades", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 202 - 203.
Paul Doherty and Don Rathjen, "Diffraction", Exploratorium Science Snackbook, p. 38.1 - 38.2.
Joseph Frick, "#191 - Experiments on Diffraction", Physical Technics: Or Practical Instructions for Making Experiments in Physics and the Construction of Physical Apparatus with the Most Limmited Means, p. 222.

6C10.15 - Laser and Adjustible Slit