October 2025
Volume 93, Issue No. 10
Spectroscopic characterization of 3D photonic crystals
We present a series of optical experiments on 3D photonic crystals suitable for advanced physics laboratory courses or senior capstone projects. The crystals are fabricated from a water solution of monodisperse polystyrene microspheres, with diameters of 200, 220, 370, and 430 nm, using the vertical deposition method. The microspheres self-assemble into a face-centered cubic structure, resulting in a pseudo-bandgap along the [111] direction. We study this bandgap through reflection and angle-resolved transmission spectroscopy using a fiber-optic-coupled USB spectrometer. Our experimental results align closely with predictions based on photonic band diagrams and the Bragg–Snell law, demonstrating the scale invariance of Maxwell's equations. These experiments provide an accessible and engaging platform for students to explore the physics of light interaction with periodic structures.
EDITORIAL
In this issue: October 2025 by John Essick; Jesse Kinder; Claire A. Marrache-Kikuchi; Beth Parks; Todd Springer. DOI: 10.1119/5.0299215
LETTERS TO THE EDITOR
Comment on “Plasma waves in a different frame” [Am. J. Phys. 88, 723–733 (2020)] by Sudip Sengupta. DOI: 10.1119/5.0254729
Response to “Comment on ‘Plasma waves in a different frame’” [Am. J. Phys. 93, 771–772 (2025)] by A. Macchi. DOI: 10.1119/5.0290846
AWARDS
2025 AAPT award citations at the summer meeting in Washington, District of Columbia. DOI: 10.1119/5.0299710
PAPERS
A colored line on an optical disk by Wittaya Kanchanapusakit; Pattarapon Tanalikhit; Apichart Pattanaporkratana; Phuphinyo Limchantra; Supakorn Buarouang; Pornrat Wattanakasiwich. DOI: 10.1119/5.0211333
Editor's Note: When you hold a CD or a DVD under a lamp, you may sometimes see a colored line caused by the interference of light rays dispersed by the disk's grooves. This paper investigates why, when the lamp is sufficiently close to the disk, the colored line is not of a single color but instead exhibits a gradation of colors. This article could be useful as a classroom demonstration in undergraduate optics courses or as a puzzle one could ask students to solve.
Common principles behind rainbows and boat wakes by Eduardo A. Jagla; Alberto G. Rojo. DOI: 10.1119/5.0226164
Editor's Note: This paper highlights the connection existing between the formation of rainbows, the pattern of boat wakes, and the evolution of certain quantum wave packets, by showing how all three phenomena arise from a common wave principle: Airy interference. Starting from the geometry of cubic wavefront and using undergraduate-level concepts and mathematics, the authors show how these structures lead to bright focusing effects and oscillatory patterns, such as the supernumerary arcs in rainbows, the fringes near the Kelvin wake cone behind boats, and the sharp boundaries in dispersive quantum systems. This unified framework could be useful in undergraduate quantum mechanics, fluid mechanics, optics, waves, or mathematical physics classes.
Listen! it's a phase transition. The sound of a shape memory alloy by Carlo Andrea Rozzi; Annamaria Lisotti; Guido Goldoni; Valentina De Renzi. DOI: 10.1119/5.0217522
Editor's Note Tired of boiling water to showcase phase transitions in class? Try dropping a NiTi bar on the ground, first at ambient temperature, and a second time after heating the bar above, typically, 70 °C. In the first case, you'll hear a dull thud, in the second case a clear, higher frequency ring. This article explains why. Spoiler: The change in sound can be explained by the martensitic phase transition undergone by NiTi. Appropriate for undergraduate mechanics, acoustics, or phase transition classes.
Unblowing bubbles: Understanding the physics of bubble deflation through a straw by Daniele Battesimo Provenzano; Andrea Stefanini. DOI: 10.1119/5.0254263
Editor's Note: Who hasn't enjoyed blowing bubbles through a straw? But have you ever considered the physics of unblowing a bubble? Instead of blowing the bubble off the end of the straw, it can be allowed to deflate. There are two simple models for the deflation process: one limited by the viscous flow through the straw, and the other limited by the inertia of the air inside the bubble. However, for some fairly typical ranges of straws and bubbles, neither model dominates, and instead, both need to be considered. This manuscript will help instructors understand the models, and it could lead to at-home or in-lab experiments at a variety of levels of complexity.
ADVANCED TOPICS
Scattering from the charge radius of a neutral particle by Max Ketterer; David C. Latimer. DOI: 10.1119/5.0232699
Editor's Note: Few systems lend themselves to analysis within classical mechanics, quantum mechanics, and quantum field theory. Rutherford scattering is a notable exception. This article introduces another: a point charge surrounded by a compensating shell of opposite charge. Though the net charge is zero, scattering calculations reveal the influence of the internal charge distribution. The authors present parallel treatments using classical scattering theory, the Born approximation, and quantum field theory—emphasizing physical insight alongside mathematical analysis. The model can serve as a useful teaching example in any of these contexts and highlights how classical and quantum analyses can diverge, in contrast to the familiar case of Rutherford scattering.
INSTRUCTIONAL LABORATORIES AND DEMONSTRATIONS
The study of gamma radiation emitted by natural objects in a student laboratory by Viacheslav V. Kaminskiy; Oleg I. Meshkov; Elena V. Starostina. DOI: 027152210.1119/5.0271522
Editor's Note: This paper presents a set of laboratory activities in which students identify the source of gamma-ray radiation from objects encountered in everyday life. Using a high-purity germanium detector, gamma spectra are acquired from sources such as building materials in laboratory walls, potassium chloride in garden-store fertilizer, and crushed granite. Students verify the safe level of this gamma radiation by converting their measurements to units of equivalent banana dose. The authors provide clear explanations of both the theoretical background and laboratory procedures required for carrying out the described activities as well as alternatives for purchasing the experimental setup.
Polarization spectroscopy of the 5S –5D5/2 two-photon transition in rubidium by H. C. Busch; C. F. Busch; C. I. Sukenik. DOI: 10.1119/5.0254590
Editor's Note: This paper describes a polarization spectroscopy experiment in which the 5S–5D transition in rubidium vapor is excited by the absorption of two photons of the same frequency. The authors first provide necessary theoretical background on polarization spectroscopy, then go on to describe their experimental setup. Experimental results are compared with predicted theoretical lineshapes as well as the expected intensity dependence of the two-photon transition. The experiment, which can be performed with a single diode laser, explores topics in atomic physics and optics. It is suitable for the advanced undergraduate instructional laboratory and offers a valuable complement to existing two-photon experiments in rubidium vapor already performed in undergraduate and graduate teaching laboratories.
Spectroscopic characterization of 3D photonic crystals by Michael Hennessey-Wesen; Dimitri Lezcano; Gina Mayonado; Wesley Gant; Shabbir M. Mian; Valentina Robbiano; Franco Cacialli. DOI: 10.1119/5.0267463
Editor's Note: This paper offers an accessible introduction to photonic band concepts as well as a feasible method for fabricating and characterizing three-dimensional photonic crystals consisting of polystyrene microspheres. Complementary theoretical derivations of the photonic band gap based on Maxwell's equations and the Bragg–Snell law are provided, and then photonic crystal effects are demonstrated experimentally through reflection and angle-resolved transmission spectroscopy measurements. The paper presents a welcome opportunity to initiate upper-level students to modern photonics concepts in an advanced instructional laboratory or a senior capstone project.
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