Doppler Free LASER Spectroscopy
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Transcript of Doppler Free LASER Spectroscopy
Doppler Free LASER Spectroscopy
It’s a headache for you
And a migraine for me!
LASER Spectroscopy Setup
• Tunable diode LASER
LASER Spectroscopy Setup
• Tunable diode LASER
– Diffraction grating mirror
– Piezo-electric actuator
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)
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
• Rubidium cell
– Probe, reference, and pump beams pass through Rubidium atoms
• Rubidium cell
– Probe, reference, and pump beams pass through Rubidium atoms
• Photodiode differential amplifier
– Subtracts the two signals from the reference and probe beams
Probe beam
Reference beam
Output to Oscilloscope
• 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
The Statistical Doppler Effect
• Gaussian distribution of velocities
– Fast moving atoms
The Statistical Doppler Effect
• Gaussian distribution of velocities
– Fast moving atoms
– Slow moving (stopped) atoms
The Statistical Doppler Effect
• Gaussian distribution of velocities
– Fast moving atoms
– Slow moving (stopped) atoms
• blurring of the spectral lines
How Saturation Spectroscopy Undoes the Doppler Blurring Effects
• Reference beam:
– Passes through only Rubidium
– Interacts with all the atoms in its path
How Saturation Spectroscopy Undoes the Doppler Blurring Effects
• Reference beam:
– Passes through only Rubidium
– Interacts with all the atoms
• Probe beam:
– Passes through Rubidium
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:
How Saturation Spectroscopy Undoes the Doppler Blurring Effects
• Reference beam:
– Passes through only Rubidium
– Interacts with all the atoms
• Probe beam:
– Passes through Rubidium
– Ignores “stationary” atoms at transition frequency becausethey are already excited by the pump beam
and “pump beam”
• Pump beam:– Counter-propagates through probe beam and excites the
atoms in its path
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
The Tapered LASER Amplifier
• Requirements:
– Delicate temperature control
– Input beam
• Drives the amplifier at the given frequency
Super stable seed beam
Unthinkably powerful output beam
Amplification Process
Excited State
Gain Medium (semiconductor)
Ground State
Part
ially
ref
lect
ive
mir
ror
Mir
ror
Excited State
Gain Medium (semiconductor)
Ground State
