lithium niobateLiNbO3
PPLN Λ = 6.82 µm · 1064 → 532 nm · 2 px/µm
lithium niobate / 04 Quirks / 4.5

4.5 Optical damage thresholds: the intensity ladder

L1 Phenomenon

three meanings of damage

Damage in lithium niobate means three different things at three intensity scales. Photorefraction distorts a beam, in Fe-doped crystals already at 10 mW/cm2, and can be erased. Light-induced coloring appears under strong pulses: GRIIRA vanishes when the green light stops; the gray track is stable in congruent crystals until erased by light or heat. Laser-induced breakdown, in the GW/cm2 range for nanosecond pulses, is permanent physical destruction.

Intensity ladder: one log axis, value left, definition rightfluence on its own axis; no conversion
10⁻²10⁻¹10⁰10¹10²10³10⁴10⁵10⁶10⁷10⁸10⁹10¹⁰W/cm²10 mW/cm² cwphotorefraction observed, no threshold; blue-green, LiNbO3:Fe0.1 kW/cm² cwphotorefractive damage threshold, NSLN; green, 10 min1 kW/cm² cwphotorefractive damage threshold, CLN; green, 10 min> 8 MW/cm² cwno damage, CLN:6% MgO and NSLN:1.8% MgO; green, 10 min2.5 kW/cm² cwGRIIRA measured, 532 nm pump; vanishes when pump stops~100 MW/cm² pulsedgray (dark) trace after repeated pulses; stable in CLNGW/cm² range pulsedlaser-induced breakdown, 1064 nm, pulse-length dependent; permanentvendornot amaterialconstant10⁻¹10⁰10¹10²J/cm²14
hover a rung: value, regime, locator
and definition
span, cw onset to breakdown
11-12 decades
vendor
100-300 MW/cm², 10 ns
fluence, 1 mol% MgO:LN
14 J/cm², 1 ns

Breakdown thresholds scatter: surface and bulk damage differ and depend on polishing and defects; measured values are often far below literature values (p. 51). Intensity and fluence are not interchangeable without the pulse shape.

Regime
Highlight
rungs Volk & Wöhlecke 2009, pp. 51-52, Table 4.3P-compfluence Furukawa et al. 1991reportedvendor data sheets V

Three kinds of damage, 11-12 decades

reversible at the bottom, permanent at the top
10⁻²10⁰10²10⁴10⁶10⁸10¹⁰W/cm²10 mW/cm²reversible, cw0.1 kW/cm²reversible, cw1 kW/cm²reversible, cw> 8 MW/cm²no damage, cw2.5 kW/cm² GRIIRAreversible, cw~100 MW/cm²reversible, pulsedGW/cm² rangepermanent, pulsedvendor, not a material constant14 J/cm², 1 nsJ/cm²
Regime
Crystal
Hover a rungvalue and definition

Fe-doped LN is distorted by cw light at 10 mW/cm²; breakdown needs GW/cm² nanosecond pulses. The fluence axis on the right is separate: intensity and fluence do not convert without the pulse shape.

rungs Volk & Wöhlecke 2009, pp. 51-52, Table 4.3P-compfluence Furukawa et al. 1991reportedvendor data sheets V

L2 The ladder

RegimeValueConditionsSource
Photorefraction onset10 mW/cm2, no thresholdcw blue-green, LiNbO3:FeVolk & Wöhlecke 2009, p. 52P-comp
Photorefractive damage threshold, CLN1 kW/cm2cw green, 10 minVolk & Wöhlecke 2009, Table 4.3P-comp
Photorefractive damage threshold, CLN:6% MgO and NSLN:1.8% MgO> 8 MW/cm2cw green, 10 minVolk & Wöhlecke 2009, Table 4.3P-comp
GRIIRA, measurement condition2.5 kW/cm2cw 532 nm pump; IR absorption vanishes when the pump stopsVolk & Wöhlecke 2009, Fig. 4.14, p. 96P-comp
Coloration (gray or dark trace)about 100 MW/cm2pulsed, after repeated pulsesVolk & Wöhlecke 2009, p. 51P-comp
Laser-induced breakdownGW/cm2 rangepulsed, 1064 nm, pulse-length dependentVolk & Wöhlecke 2009, p. 51P-comp
Bulk laser damage fluence, 1 mol% MgO:LN14 J/cm21.053 µm, 1 nsFurukawa et al. 1991reported
Vendor laser damage thresholds100-300 MW/cm210 ns, 1064 nm; not a material constantvendor data sheets V

Conflict. The laser damage fluence is 14 J/cm2 in the Furukawa 1991 abstract and 14.6 J/cm2 in Volk & Wöhlecke p. 51; the abstract value is used.

L3 Scatter and units

surface, bulk, pulse shape
  • Breakdown thresholds scatter because surface and bulk damage differ and depend on polishing and defects; measured values are often far below literature values (p. 51 P-comp).
  • Intensity (W/cm2) and fluence (J/cm2) are not interchangeable without the pulse shape; the ladder keeps them on separate axes.
  • Vendor thresholds lack traceable measurement conditions.
  • Photorefractive thresholds are operational (beam distortion after a stated time) and depend on beam size and observation time (4.2 L3).

Sources

  1. Volk & Wöhlecke 2009Tatyana Volk, Manfred Wöhlecke, Lithium Niobate: Defects, Photorefraction and Ferroelectric Switching. Springer Series in Materials Science 115 (2009), doi:10.1007/978-3-540-70766-0.Read: selected chapters: Ch. 2.2 (pp. 14-19), Ch. 3 (pp. 51-61), Ch. 4 (pp. 75-77, 82-85, 94-97), Sec. 7.1.3 (p. 168)
  2. Furukawa et al. 1991Y. Furukawa, A. Yokotani, T. Sasaki et al., Investigation of bulk laser damage threshold of lithium niobate single crystals by Q-switched pulse laser. Journal of Applied Physics 69 3372-3374 (1991), doi:10.1063/1.348537.Read: abstract