Event Title

The Talbot Effect

Presenter Information

Malia Kawamura, Colby CollegeFollow

Location

Diamond 341

Start Date

1-5-2014 9:00 AM

End Date

1-5-2014 10:50 AM

Project Type

Presentation- Restricted to Campus Access

Description

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 image repetitions at integral Talbot lengths, while at fractional Talbot lengths image repetitions also occur, but with greater spatial periodicity. We use green and red helium neon lasers and Ronchi rulings to gather CCD camera images of Talbot revivals. Additionally, a photodiode captures light intensity as a function of time as a grating is moved. The camera and photodiode results are in good qualitative agreement with theory. We also obtain a few Talbot Lau images of fringes using a sodium lamp as an 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 the built-in defocus function. TEM image analysis completed with Fiji confirms that fractional revivals appear in the expected order. While the TEM position readings of the Talbot revivals are not as theoretically expected, this is due to uncertainty in the grating periodicity and TEM defocus function. Further experiments could include fabricating smaller gratings using e-beam lithography and calibrating the TEM defocus function using the Talbot effect.

Faculty Sponsor

Duncan Tate; Liz McGrath

Sponsoring Department

Colby College. Physics and Astronomy Dept.

CLAS Field of Study

Natural Sciences

Event Website

http://www.colby.edu/clas

ID

52

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May 1st, 9:00 AM May 1st, 10:50 AM

The Talbot Effect

Diamond 341

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 image repetitions at integral Talbot lengths, while at fractional Talbot lengths image repetitions also occur, but with greater spatial periodicity. We use green and red helium neon lasers and Ronchi rulings to gather CCD camera images of Talbot revivals. Additionally, a photodiode captures light intensity as a function of time as a grating is moved. The camera and photodiode results are in good qualitative agreement with theory. We also obtain a few Talbot Lau images of fringes using a sodium lamp as an 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 the built-in defocus function. TEM image analysis completed with Fiji confirms that fractional revivals appear in the expected order. While the TEM position readings of the Talbot revivals are not as theoretically expected, this is due to uncertainty in the grating periodicity and TEM defocus function. Further experiments could include fabricating smaller gratings using e-beam lithography and calibrating the TEM defocus function using the Talbot effect.

http://digitalcommons.colby.edu/clas/2014/program/302