Building a Green Laser Source via Second Harmonic Generation

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Building a Green Laser Source via Second Harmonic
Generation Diana Parno (dparno_at_cmu.edu) for the
Hall A Compton Polarimetry Group
Motivation Polarimeter Upgrade
SHG Apparatus

• The upgrade of the Hall A Compton Polarimeter,
  which will double its analyzing power and allow
  1 accuracy in an hour of continuous electron
  beam polarization measurements, requires a 532 nm
  laser with
• Narrow linewidth
• PZT-driven fast-feedback ability for locking to
  a Fabry-Perot cavity
• Temperature tuning
• We propose to construct a green laser via
  single-pass second harmonic generation (SHG), the
  nonlinear optical process at the heart of green
  laser technology. Our advantages
• Reliable infrared seed laser
• New, more efficient crystals (e.g. lithium
  niobate, LiNbO3)
• Better available crystal structures (periodic
  poling)

Second Harmonic Generation

• The nonlinear optical process of second
  harmonic generation (SHG) occurs inside a crystal
  for a pump wave of frequency ?
• The pump wave stimulates a polarization that
  oscillates at 2?.
• This polarization radiates an EM wave with
  frequency 2?.
• Energy is transferred from the pump to the
  second harmonic while the phase difference
  between the two EM waves is less than 180.

Results and Future Work

• Results
• We have achieved a green output of about 15 mW
  with a 700-mW continuous-wave infrared input
• We have found the optimal crystal temperature
  range
• Future Work
• Power instabilities are likely caused by
  temperature problems, so we are seeking new
  temperature control solutions
• Better beam separation (a chicane of four
  dichroic mirrors) will improve quality of green
  output
• Coupling the infrared laser to a fiber amplifier
  will allow us to achieve several hundred mW of
  green power

• How do we ensure that energy transfer always goes
  the right way?

• Birefringent phase matching (BPM) Prevent phase
  mismatch by controlling incident angle both
  waves see the same refraction index. Not possible
  for LiNbO3!
• Quasi-phase matching (QPM) Introduce periodic
  domain reversals (periodic poling) to regularly
  induce a 180 phase shift to compensate for phase
  mismatch