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Our Vacuum Chamber
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Making Bose Einstein Condensates
BEC is a special state of matter which we get once we cool bosons to such a low temperature that all the bosons fall to the ground state. In our lab, we make all optical BEC's of rubidium-87 atoms. The first step of the process is to load atoms into a magneto-optical trap (MOT). Subsequently, the atoms are transferred to a dipole trap formed at the focus of a CO2 laser (10.6 micron wavelength), where they are evaporatively cooled to make BEC's.
Imaging Procedure
The only measurements that can be performed on the atoms inside the vacuum chamber, especially after they have been condensed, are optical. This is because any more invasive method would completely destroy the properties of the cloud. Therefore, we take absorption images of the clouds with a CCD camera. Resonant light is shone on the clouds and the shadow cast is caught in the camera. From this, the optical depth and hence the number of atoms in the cloud, along with other properties, can be estimated.
Software
We use a Starlight MX7 CCD camera to take our pictures. The setup consists of two computers- a timing computer (Timer) and a control computer (Controller). The Controller runs the GUI where one can specify the size, exposure etc. of the picture. The Timer manages the various components on the optical table through a DIO 128 board. The picture is received by the Controller.
We have two versions of camera control software:
Simple Visual Basic Executable: We modified the original driver code that came with the camera to make an executable that takes pictures of clouds and outputs them as comma delimited ASCII files. These text files can be opened by Matlab or other programs for viewing the images. A screenshot of the GUI is shown on the right. You can download the source code and the executable here.
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Matlab Program with Fitting Routines:
Here, the VB routine that communicates with the camera has been turned into an ActiveX object which can be called from a Matlab program. The Matlab program comes with a GUI and also provides options to fit the picture of the cloud to Gaussian distributions thereby estimating the expanse of the cloud and the number of atoms in it. You can download a zip file with the source code for the Matlab routines, VB code as well as instructions here.
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Published By
Pf. Dwight Whitaker,
Arjun Sharma.
Department of Physics,
Williams College
Williamstown, MA, 01267
Email Dwight Whitaker:
dwhitaker@williams.edu
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For Software Help
Email Arjun Sharma:
07as@williams.edu
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Page Designed By:
Arjun Sharma
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