Imaging System of a Bose-Einstein Condensation Experiment, and its Automation
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Transcript of Imaging System of a Bose-Einstein Condensation Experiment, and its Automation
Imaging System of a Bose-Einstein Condensation
Experiment, and its Automation
Fabien Lienhart
U.C BerkeleyPhysics departmentStamper-Kurn’s group
August, 29th 2003
Plan
• Recent steps forward in the BEC experiment
• The Imaging System
• Automation of the imaging system: Visual Basic in WinView
Improvements and breakthroughs on the BEC
experiment
• Ultrahigh Vacuum fixed• MOT laser brighter and monomode• Polarization Gradient cooling set• First efficient magnetic trappings• Next (last?) step…
Back to a Ultra-High Vacuum
Problem: water leaking from a coil in the vacuum chamber
Open the chamber, fix the leak, close the chamber and Back to the vacuum
•Rotary pump
•Turbomolecular pump
•1 week baking-out, monitored by a Rare Gas Analyser
•Gauge limit
10-3
10-7
10-11
Torr
MOT LaserHow things work… Problem
Ugly beam which could be stronger
Solutions•Tapered amplifier: up to 300 mW•Polarization maintaining
optical fiber
Results •After the fiber: - 70 mW
- monomode - good shape
•Up to 3 billion atoms trapped
Optimizing pg-coolingHow things work…
Easy case of lin –lin lightImprovements• Better beam shape• Transition between the two pg-cooling steps found: optimization of T and N
Results30 K reached
(Time of flight measurement)
First efficient magnetic trappings
How Ioffe-Pritchard trap works…
Results• More than 600 million atoms trapped• Lifetimes ranking from 15s (low Bias-Field) to 50s• Adiabatic compression achieved
The Imaging System
• The constraints• The experimental device• Characterization of the system• Results and future work
The Constraints
• Requirements of the system- Resonant light has to be used: 2-to-3 beam- Top-bottom axis- Keep the polarization of the light- Three very different magnifications: ~ ½, 5 and
16
• The difficulties- Top-bottom axis is already crowded!- Only a few gold mirrors can be used at 45o
- Precise magnification needs to be known (quantitative imaging) and no way to place a fine object in the center of the trap!
The Experimental Device
Characterization of the System
ResultsMag ½Magnification: 0.510 0.015Resolution: 80 m (close to Camera limit)Not to sensitive to the position of the MOTBut sensitive to the angle of the last lens (distortion)
Mag 5Magnification: 4.60 0.01Resolution: 8.7 m (close to diffraction limit)No distortionResolution very sensitive to the position of the cloud
Mag 16Magnification: 12.0 0.6Resolution: 14 mPosition of the camera affects the magnification (.35/cm)
without really changing the resolutionVery sensitive to the angle of the last lens (distortion)
Automation of the Imaging System
• How WinView works
• Adding buttons with WinView
• Example of routine: rotating the images
• Future work
How WinView works
•WinView controls the camera•Automating WinView:
Using MacrosEasy, but limited and buggy
Or…
Adding buttons with Visual Basic1. Write your script in VB
Object Oriented ProgrammingClasses which implement WinView
2. Transform it into a DLL
3. Register the DLL
4. A new icon should appear inWinView’s taskbar
The implemented buttons
• Close All - closes all the windows
• AutoSave - saves all the windows with the date
• QuickASCII - saves the image as a text
• AbsorptionLoop - cycles absorption pictures
• RotateFrame - rotates the pictures
Example: the rotation
ProblemMatrix index must be integer numbersWhich is not the case after rotation
SolutionsImplementation of various algorithms
1. Closest neighbor2. Gaussian interpolation3. Bicubic interpolation4. -Spline method: 2 ideas
leading to the best results
Idea 1 - Three-pass rotation
Idea 2 – Efficient 1D interpolationCubic b-Spline
Third order Basis Piecewise polynomials
Advantages- Normalized contributions- Compact support -> local control- Interpolated function is C2
- Fast implementation: z-transform of the convolution givesan efficient recursive algorithm
Performances of the different methods
A. OriginalB. Clothest neighborC. Gaussian interpolationD. Bicubic interpolationE. -Spline method
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B C D E
Time (in s) taken for a rotation
Conclusion
Work achieved- Imaging system: characterization and limits of the system- WinView: add-ins
In the next month-Imaging system:
- way to easily calibrate the system- try different lens for mag ½ and 16
- WinView: gaussian fit of the profile of the cloud