June 2018 Issue, Volume 86, No. 6June 2018 issue of American Journal of Physics


Diffraction effects in mechanically chopped laser pulses

A mechanical beam chopper consists of a rotating disc of regularly spaced wide slits which allow light to pass through them. A continuous light beam, after passing through the rotating disc, is switched-on and switched-off periodically, and a series of optical pulses are produced. The intensity of each pulse is expected to rise and fall smoothly with time. However, a careful study has revealed that the edges of mechanically chopped laser light pulses consist of periodic intensity undulations which can be detected with a photo detector. In this paper, it is shown that the intensity undulations in mechanically chopped laser pulses are produced by diffraction of light from the rotating disc, and a detailed explanation is given of the intensity undulations in mechanically chopped laser pulses. An experiment presented in this paper provides an efficient method to capture a one dimensional diffraction profile of light from a straight sharp-edge in the time domain. In addition, the experiment accurately measures wavelengths of three different laser beams from the undulations in mechanically chopped laser light pulses.


Letters to the Editor

Comment on Sanders Guest Editorial by B. Cameron Reed. DOI: 10.1119/1.5036944.


Diffraction effects in mechanically chopped laser pulses by Samridhi Gambhir, and Mandip Singh. DOI: 10.1119/1.5029821.

Quantum entanglement with Freedman's inequality by Jed Brody, and Charlotte Selton. DOI: 10.1119/1.5036619.

Theory and experiment on charging and discharging a capacitor through a reverse-biased diode by Arijit Roy, Abhishek Mallick, Aparna Adhikari, Priyanka Guinand and Dibyendu Chatterjee. DOI: 10.1119/1.5026994.

On Faraday's law in the presence of extended conductors by Luis Bilbao. DOI: 10.1119/1.5034445.

The metallic sphere in a uniform ac magnetic field: A simple and precise experiment for exploring eddy currents and non-destructive testing by Michael L. Honke, and Christopher P. Bidinosti. DOI: 10.1119/1.5034350.

Sympathetic resonance by Lawrence N. Virgin. DOI: 10.1119/1.5025037.

Drag and lift forces between a rotating conductive sphere and a cylindrical magnet by Mark A. Nurge, Robert C. Youngquist, and Stanley O. Starr. DOI: 10.1119/1.5024220.

On a nonlinear Newtonian gravity and charging a black hole by Michael R. R. Good. DOI: 10.1119/1.5030543.

Exploring cogging free magnetic gears by Stefan Borgers, Simeon Völkel, Wolfgang Schöpf, and Ingo Rehberg. DOI: 10.1119/1.5029823.

Notes and Discussions

Comment on “Sliding down an arbitrary curve in the presence of friction” by F. González-Cataldo, G. Gutiérrez, and J. M. Yáñez, Am. J. Phys. 85(2), 108–114 (2017) by L. A. del Pino, and S. Curilef. DOI: 10.1119/1.5029480.

The pre-Newtonian meaning of the word “weight”; a comment on “Kepler and the origins of pre-Newtonian mass” [Am. J. Phys. 85, 115–123 (2017)] by K. M. Browne. DOI: 10.1119/1.5027490.

Apparatus and Demonstration Notes

Electrical source of pseudothermal light by Tom A. Kuusela. DOI: 10.1119/1.5029829.

Book Reviews

From Photon to Neuron: Light, Imaging, Vision by Sönke Johnsen. DOI: 10.1119/1.5022186.

Books Received

American Journal of Physics 86, 480 (2018). DOI: 10.1119/1.5035564.


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