The Coherent 899 Ti:Sapphire laser at I411

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The Coherent 899 TiSapphire laser at I411
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What is laser light?

• Light Amplification by Stimulated Emission of
  Radiation

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Properties of laser light

• Coherence
• Intensity (brightness)
• Spectral resolution (monochromaticity)
• Spacial resolution (directionality)
• Temporal resolution
• Polarization

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Coherent 899 TiSa laser
Upper fold mirror M5
Faraday rotator
Optical rotator
Optical diode
TitaniumSapphire crystal
Lower fold mirror M3
Birefringent filter
Intermediate fold mirror M1
Output coupler M4
Focusing lens L1
Pump mirror P1
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Upper fold mirror M5
Focusing lens L1
Intermediate fold mirror M1
TitaniumSapphire crystal
Pump mirror P1
Pump beam
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Upper fold mirror M5
L1 and M1
Birefringent filter
TitaniumSapphire crystal
Pump mirror P1
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Coherent 899 TiSa laser

• Pumped with Coherent Verdi 10W NdVanadate laser
  (max. output 10.5W)
• Verdi emits at 532 nm (2.33 eV)
• Tuning range of 899 TiSa 680 nm 1035 nm ( 1.2
  eV - 1.8 eV)
• Output power 1 1.5 W after output coupler
  (reached so far)
• CW operation

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Reached recently with Rb experiments
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Coherent 899 TiSa laser

• Passive frequency control with three plate
  birefringent filter, bandwidth of 2 GHz or 8
  µeV
• Inserting intercavity etalon assembly -gt
  bandwidth 10 MHz or 0.04 µeV
• Active frequency control bandwidth down to 500
  kHz RMS (2 neV)

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Coherent 899 TiSa laser

• Outcoming laser light vertically linearly
  polarized
• Guiding optics change polarization
• Polarizing optics before target needed
• Use of wave plates to change polarization
• Quarter wave plate linear polarized to
  circualrly polarized or vice versa
• Half wave plate rotates polarization direction
  of linearly polarized light

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Optical setup after laser

• Typically 6 mirrors are used
• Reflectivity 0.9 - 0.95
• 0.9560.74
• Losses also due to focusing optics, polarizing
  optics and beamline window
• Due to losses laser power of 1.2 W at before
  entering BL 660 mW (measured) at I411

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Optical setup after laser

• At FINEST 2 mirrors should be enough
• 0.9520.9
• 1.2 W output should yield 800 mW before
  entering BL

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Extending the tuning range Frequency doubling

• Use of non-linear effects for second harmonic
  generation (SHG)
• High input power needed
• Relatively low conversion efficiency, typically
  12 (max.)
• Extends the tuning range towards higher energies

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Second harmonic generation

• The electric field of the incident light causes
  electric polarization in a transparent medium
• Polarization propagates together with the
  electromagnetic field in the form of a
  polarization wave
• Nonlinear polarization waves can arise in
  non-centrosymmetric crystals

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Second harmonic generation
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Second harmonic generation

• So what happens
• Electromagnetic wave generates a polarization
  wave in the crystal
• Polarization wave has double the frequency of the
  fundamental wave
• Polarization wave drives a new electromagnetic
  wave
• The new electromagnetic wave has the same
  frequency as the polarization wave -gt frequency
  doubled light

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Spectra-Physics WaveTrain
Piezoelectric transducer
Prism
Focusing mirror M2
Nonlinear crystal
Focusing mirror M1
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532nm BBO
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810nm LBO
770nm LBO
720nm LBO
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Spectra-Physics WaveTrain

• So far only 1mW has been achieved for frequency
  doubled light (blue light for Al)
• The maximum for the crystal at this wavelength
  should be near 80 mW
• This could be caused by poor alignment
• Much higher power is needed to even bring the
  light outside