Imaging System of a Bose-Einstein Condensation Experiment, and its Automation Fabien Lienhart U.C Berkeley Physics department Stamper-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 Torr

MOT Laser How 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-cooling How things work… Easy case of lin –lin light Improvements Better beam shape Transition between the two pg-cooling steps found: optimization of T and N Results 30  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 45 o -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

Results Mag ½ Magnification:0.510  Resolution:80  m (close to Camera limit) Not to sensitive to the position of the MOT But sensitive to the angle of the last lens (distortion) Mag 5 Magnification:4.60  0.01 Resolution:8.7  m (close to diffraction limit) No distortion Resolution very sensitive to the position of the cloud Mag 16 Magnification:12.0  0.6 Resolution:14  m Position of the camera affects the magnification (.35/cm) without really changing the resolution Very 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 Macros Easy, but limited and buggy Or…

Adding buttons with Visual Basic 1. Write your script in VB Object Oriented Programming Classes which implement WinView 2. Transform it into a DLL 3. Register the DLL 4. A new icon should appear in WinView’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 Problem Matrix index must be integer numbers Which is not the case after rotation Solutions Implementation of various algorithms 1. Closest neighbor 2. Gaussian interpolation 3. Bicubic interpolation 4.  -Spline method: 2 ideas leading to the best results

Idea 1 - Three-pass rotation

Idea 2 – Efficient 1D interpolation Cubic b-Spline Third orderBasisPiecewise polynomials Advantages - Normalized contributions - Compact support -> local control - Interpolated function is C 2 - Fast implementation: z-transform of the convolution gives an efficient recursive algorithm

Performances of the different methods A.Original B.Clothest neighbor C.Gaussian interpolation D.Bicubic interpolation  -Spline method

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