Doppler Free LASER Spectroscopy

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Doppler Free LASER Spectroscopy

• Its a headache for you
• And a migraine for me!

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LASER Spectroscopy Setup

• Tunable diode LASER

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LASER Spectroscopy Setup

• Tunable diode LASER
• Diffraction grating mirror
• Piezo-electric actuator

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LASER Spectroscopy Setup

• Tunable diode LASER
• Diffraction grating mirror
• Piezo-electric actuator
• Miscellaneous Optics
• Beam-splitter splits LASER beam into two probe
  beams (weak) and a pump beam (strong)

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LASER Spectroscopy

• Tunable diode LASER
• Diffraction grating mirror
• Piezo-electric actuator
• Miscellaneous Optics
• Beam-splitter splits LASER beam into two probe
  beams (weak) and a pump beam (strong)
• Mirrors reflect stronger pump beam to
  counter-propagate against probe beam

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• Rubidium cell
• Probe, reference, and pump beams pass through
  Rubidium atoms

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• Rubidium cell
• Probe, reference, and pump beams pass through
  Rubidium atoms
• Photodiode differential amplifier
• Subtracts the two signals from the reference and
  probe beams

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I made this!
Mathmagical Manipulation!
Probe beam
Output to Oscilloscope
Reference beam
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• Rubidium cell
• Probe, reference, and pump beams pass through
  Rubidium atoms
• Photodiode differential amplifier
• Subtracts the two signals from the reference and
  probe beams
• Oscilloscope
• Creates a real-time plot of absorption vs.
  frequency

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The Statistical Doppler Effect

• Gaussian distribution of velocities
• Fast moving atoms

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The Statistical Doppler Effect

• Gaussian distribution of velocities
• Fast moving atoms
• Slow moving (stopped) atoms

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The Statistical Doppler Effect

• Gaussian distribution of velocities
• Fast moving atoms
• Slow moving (stopped) atoms
• blurring of the spectral lines

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How Saturation Spectroscopy Undoes the Doppler
Blurring Effects

• Reference beam
• Passes through only Rubidium
• Interacts with all the atoms in its path

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How Saturation Spectroscopy Undoes the Doppler
Blurring Effects

• Reference beam
• Passes through only Rubidium
• Interacts with all the atoms
• Probe beam
• Passes through Rubidium

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How Saturation Spectroscopy Undoes the Doppler
Blurring Effects

• Reference beam
• Passes through only Rubidium
• Interacts with all the atoms
• Probe beam
• Passes through Rubidium

and pump beam

• Pump beam

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How Saturation Spectroscopy Undoes the Doppler
Blurring Effects

• Reference beam
• Passes through only Rubidium
• Interacts with all the atoms
• Probe beam
• Passes through Rubidium

and pump beam

• Pump beam
• Counter-propagates through probe beam and
  excites the
• atoms in its path

• Ignores stationary atoms at transition
  frequency because
• they are already excited by the pump beam

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Application

• Use the LASER, which is now accurately locked on
  a precise frequency, to trap atoms
• Instead of using multiple LASERs, feed the locked
  LASER beam into a tapered amplifier

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The Tapered LASER Amplifier

• Requirements
• Delicate temperature control
• Input beam
• Drives the amplifier at the given frequency

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I made this too!
Temperature measuring device (thermistor)
Thermal Electric cooler
LASER diode current supply
Amplification Process
Unthinkably powerful output beam
Super stable seed beam
LASER diode chip
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Excited State
Partially reflective mirror
Mirror
Gain Medium (semiconductor)
Ground State
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Excited State
Gain Medium (semiconductor)
Ground State
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