Diffraction effects in mechanically chopped laser pulses

TL;DR

This paper investigates how diffraction from a rotating disc causes intensity undulations in mechanically chopped laser pulses, providing insights into diffraction effects and a method to measure laser wavelengths in the time domain.

Contribution

It demonstrates that diffraction effects produce pulse undulations and introduces a method to measure laser wavelengths using these undulations.

Findings

Diffraction causes periodic intensity undulations in chopped laser pulses.

The method accurately measures wavelengths of different laser beams.

The experiment captures diffraction profiles in the time domain.

Abstract

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. It has been shown in this paper that the intensity undulations in mechanically chopped laser pulses are produced by diffraction of light from the rotating disc and a detailed explanation of the intensity undulations is given. The experiment 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 measured wavelengths of three different laser beams from the undulations in mechanically chopped laser light pulses.