Semi automatic retrieval of temperature and density in a magneto optical trap
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Semi-Automatic Retrieval of Temperature and Density in a Magneto-Optical Trap. Dan Mickelson Supervisor: Brett D. DePaola. July 28, 2009. Introduction. My Project To design, construct, and test an apparatus to measure temperature and density in a MOT. Why am I doing this?

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Semi-Automatic Retrieval of Temperature and Density in a Magneto-Optical Trap

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Semi automatic retrieval of temperature and density in a magneto optical trap

Semi-Automatic Retrieval of Temperature and Density in a Magneto-Optical Trap

Dan Mickelson

Supervisor: Brett D. DePaola

July 28, 2009


Introduction

Introduction

  • My Project

    • To design, construct, and test an apparatus to measure temperature and density in a MOT.

  • Why am I doing this?

    • We want to better understand the conditions just before photoassociation.

Imaging beam to take measurements


Photoassociation of molecules

Incident light excites a Rb atom pair

Excites to an excited quasi-molecule state

A photon is then emitted

Results in either bound molecule, or original atom pair

Photoassociation of Molecules


Semi automatic retrieval of temperature and density in a magneto optical trap

Photoassociation with Excitation

As the molecule is formed, it follows potential curves that depend on the energy state of each atom

In MOTRIMS, atoms are excited a second time and then detected by forming a molecular ion


Magneto optical traps

Magneto-Optical Traps

  • Also known as a MOT.

  • Uses a combination of sub-resonant lasers and a magnetic field gradient.

  • Has a variety of applications

    • Allows to trap neutral atoms

    • Cools atoms to micro-Kelvin temperatures

    • Can be used for BEC

    • Most importantly (for us) allows for the conditions to achieve photoassociation

The MOTRIMS MOT


What is happening

What is Happening?

Let’s take a look in 1-dimension…

Atom

A photon is absorbed and the atom becomes excited—then a photon is emitted.

Atom

As this process proceeds, a net change in velocity occurs,

and eventually the atom is slowed to a low speed


But there s more

But There’s More…

What if an atom is moving too fast or too slow?

The atoms will not see the Doppler shift into

resonance, so we need to add something.

Also, we have nothing to keep the atoms trapped in the center.


Trapping the atoms

Trapping the Atoms

  • Combination of circularly polarized light and a magnetic field gradient

    • Zeeman shifts increase linearly from the center of the magnetic field

    • Magnetic field created by anti-Helmholtz coils

    • Light is circularly polarized to allow transitions that are spatially dependent

A formed MOT


Measuring temperature and density

Measuring Temperature and Density

  • What do we want?

    • Density measurement that is differential in both r and z.

    • Cost effective and convenient.

  • How to do it:

    • The MOT image will be a “shadow” on our detector.

    • After trap is turned off, the MOT will expand corresponding to the temperature.

Laser

MOT

y-axis

Intensity


Semi automatic retrieval of temperature and density in a magneto optical trap

Schematic of Apparatus


Progress

Progress

  • Sent the beam through the MOT

  • Used the recycled trapping beam

  • Fabricated a shutter device to fully extinguish the beam


Summary and future work

Summary and Future Work

  • Optical set-up is complete

  • Probe beam is attenuated and has adjusted frequency

  • Plenty of work still needs to be done

  • Timing mechanism to control the CCD camera and beam

  • Add a static magnetic field to define a quantization axis

  • Software to store and interpret data


Thank you for listening

Thank you for Listening

A special thanks to Charles Fehrenbach, Larry Weaver, and Kristan Corwin

This work was supported by the National Science Foundation and the U.S. Department of Energy


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