SFG and SHG with ultrafast pulses 1 Second order nonlinear - - PowerPoint PPT Presentation

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sfg and shg with ultrafast pulses
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SFG and SHG with ultrafast pulses 1 Second order nonlinear - - PowerPoint PPT Presentation

Mar 21, 2023 623 likes •735 views

SFG and SHG with ultrafast pulses 1 Second order nonlinear phenomena No centrosymmetry: Non-zero Long l (limited by coherence length, ) Angle tuning for phase matching ( D k = 0)

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SLIDE 1

1

SFG and SHG with ultrafast pulses

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SLIDE 2

Second order nonlinear phenomena

  • Angle tuning for phase matching (Dk = 0)
  • Polarization of second harmonic: Perpendicular to that of fundamental
  • High intensity of incident beam (limited by damage threshold)
  • No centrosymmetry: Non-zero
  • Long l (limited by coherence length, )
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SLIDE 3

Birefringence and Phase matching

Optic axis, Z Ordinary (o) ray Extraordinary (e) ray (Incident angle-independent refractive index) (Incident angle-dependent refractive index) Z Z no no ne ne no ≥ ne no ≤ ne Negative crystals Positive crystals no and ne for 2w no(2w) = ne(w): Phase matching direction Second harmonic generation Polarization of SH is perpendicular to that of the fundamental Birefringent crystals can have one or more optic axes

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SLIDE 4

Types of Phase matching for SFG

Pump Signal Idler Scheme e

  • Type I

e

  • e

Type II ( or IIA) e e

  • Type III (or IIB)

e e e Type IV

  • Type V (or Type 0)
  • e

Type VI (or IIB or IIIA)

  • e
  • Type VII (or IIA or IIIB)
  • e

e Type VIII (or I)

lp ≤ ls ≤ li Negative Uniaxial Positive Uniaxial

} }

Material Phase- matching type KD*P II KTP II LBO I BBO I LiNbO3 (5%MgO) I

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SLIDE 5

SHG for ultrafast pulses

Ultrashort pulses: High Intensity Spectral bandwidth Phase matching: Entire band Dk.l ≤ 2.78: Sufficient

  • R. C. Miller, Phys. Lett. 26A (1968) 177:

1 cm KDP crystal: Dn = 20 cm-1 1 cm LiNbO3 crystal: Dn = 0.5 cm-1 for 1064 nm

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SLIDE 6

Group delay

Plane waves: Phase velocity Pulsed light: Wavepacket Expanding

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SLIDE 7

Group delay

Wavepacket traveling with group velocity of Fundamental and SH: Different group velocities Amplitude of wavepacket

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SLIDE 8

Group delay

Wavepacket traveling with group velocity of Fundamental and SH: Different group velocities Difference in times of passage of fundamental and SH through NLO crystal: For

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SLIDE 9

Group delay

Wavepacket traveling with group velocity of Difference in times of passage of fundamental and SH through NLO crystal: For

Crystal Dt (ps cm-1) LiNbO3 6 LiIO3 0.7 KDP 0.08