Date of Award

2014

Document Type

Honors Thesis (Open Access)

Department

Colby College. Physics and Astronomy Dept.

Advisor(s)

Duncan A. Tate

Abstract

The goal of this project is to experimentally investigate the optical Talbot effect and the electron Talbot effect. The Talbot effect is a near-field diffraction effect which occurs when plane waves are incident upon a grating. The Talbot effect creates full grating revivals at integral Talbot lengths and revivals with greater spatial periodicity at fractional Talbot lengths. We use a green helium neon laser and Ronchi rulings to take CCD camera images of the fractional Talbot revivals directly. Additionally, a photodiode records light intensity as a function of time as a second identical grating is moved to verify the presence of Talbot revivals. The camera and photodiode results are in good qualitative agreement with theory. We also obtain Talbot Lau revival images by using a sodium lamp as the incoherent light source.

To investigate the electron Talbot effect, we first fabricate 20 nm silicon nitride gratings using electron beam lithography. Then, in a transmission electron microscope (TEM) the Talbot effect is observed and quantified using a built-in TEM defocus function. TEM image analysis with Fiji confirms that fractional revivals appear as expected qualitatively. The TEM position readings of the Talbot revivals are not as theoretically expected, but this is likely due to uncertainty in the grating periodicity and the TEM defocus function. Further experiments could include fabricating smaller gratings using Talbot-assisted lithography and calibrating the TEM defocus function using the Talbot effect.

Keywords

Talbot effect, diffraction, transmission electron microscope, TEM, laser

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