Laboratory 6

Diffraction pattern of  a circular aperture

Objective:

In this lab students will study the diffraction pattern of a circular aperture.  They will study the pattern in the Fraunhofer regime and in the Fresnel regime.

Equipment:

Laser Assembly

Beam Steering Assemblies

Lens Chuck Assemblies

Target Assemblies

Lens Kit

Targets

Meter Stick

Index Cards

Project in Optics Workbook

Procedure:

Students will follow the instructions on pages 59 - 62 of the Projects in Optics Workbook.  To assemble the components, students will refer to pages 36 - 44 in the Projects in Optics Workbook. 

Students will not make measurements with the TP1 pinhole. The  pinholes TP2 and TP3 and the 3-zone Fresnel target are part of the target set.  TP2 is the target labeled "pinhole, 50 mm", and TP3 is the target labeled "pinhole, 0.08".

Data Analysis:

Fraunhofer diffraction of a circular mask

Construct a table as shown below.

  TP2 TP3

pinhole-target distance (L)

    
diameter of first dark band (a)     
measured sinq ~ q ~ a/(2L)    
diameter of pinhole (D)    
predicted q = 1.22l/D    
D2/Ll    

Evaluate if your measurements were made in the Fraunhofer regime.  Your measurements were made in the Fraunhofer regime if D2 << Ll.
Link: When is the Fraunhofer approximation valid?

Fresnel diffraction of a circular mask

Describe several patters in the Fresnel regime and the conditions under which the patterns were produced.  Describe how the patters change when the object is moved along the beam direction.  Produce some sketches or take some pictures using the CCD camera.

Laboratory Report:

Open Microsoft Word and prepare a report using the template shown below.

Name:
E-mail address:

Laboratory 6 Report
In a few words, describe the experiment. (What?)
In a few words, state the objective of the experiment. (Why?)
Comment on the procedure.  Did you encounter difficulties or surprises? (How?)
Present your results and comment on your results.

Print out your Word document, and hand it to your instructor, or save your Word document (your name_lab6.doc) and attach it to an e-mail message to your lab instructor.