Laser Locking for Long-term Magneto-Optical Trap

Stability

Kevin W. Vogel

Advisor: Georg Raithel

Presented 07/28/04

Outline

• Magneto-Optical Trap (MOT)• Laser Locking Methods• Dichroic Atomic Vapor Laser

Locking• MOT Improvements

Magneto-Optical Trap (MOT)

• Capture and cool Rubidium atoms to μK temps

• 6 orthogonal pairs of circularly polarized counter propagating laser beams

• Anti-Helmholtz magnetic field

Diode Laser Frequency Stabilization

• Frequency changes due to temperature and diffraction grating position

• Tuned to transition frequency• Locked with a feedback circuit

Frequency ν

0 Volts

Laser Locking Methods• Saturated Absorption

Spectroscopy– Narrow locked frequency

range– Easy to lose lock– Lock time: 10 – 60 min.

• Dichroic Atomic Vapor Laser Locking (DAVLL)– Difficult to lose lock– Broader locked frequency

range– Lock time: ?

5 MHz

0 V

0 V

500 MHz

DAVLL Setup

to MOT

DAVLL Lock Signal

• Laser output is linearly polarized

• Transition shifted by Zeeman effect

• Each circular polarization is absorbed by a shifted transition

Improvements:

• Low Noise Circuit– Produces differential absorption signal

with minimal electrical noise

• Temp Controlled Permanent Magnets– Permanent magnet field strength is

temperature dependent– Keeps temp within ±0.003°C

Results43200s (07/20/04 6pm-7am)

-1-0.50

0.51

1.52

2.53

0 5000 10000 15000 20000 25000 30000 35000 40000

Time (s)

MO

T A

tom

s (1

0^5)

36000s (07/13/04 9pm - 7am)

-1-0.50

0.51

1.52

2.53

0 5000 10000 15000 20000 25000 30000 35000 40000

Time (s)

MO

T A

tom

s (1

0^5)

mode hops

14 hours!

Other MOT Improvements

• Permanent heater to clean Rubidium cell

• Larger vacuum chamber cell to increase atom flow

• Magnetic coils for larger cell• New laser grating and bracket

Acknowledgments

• Georg Raithel, Ramon Torres-Isea, Spencer Olson, Rahul Mhaskar, Tara Cubel, Aaron Reinhard, Natalya Morrow, Rui Zhang, Brenton Knuffman, Alisa Walz-Flannigan, Jae-Hoon Choi, Eberhard Hansis, Alex Povilus

• NSF• Physics Department