lithium niobateLiNbO3
PPLN Λ = 6.82 µm · 1064 → 532 nm · 2 px/µm
lithium niobate / 04 Quirks / 4.4

4.4 Green light, infrared loss: GRIIRA, BLIIRA and polarons

L1 Phenomenon

GRIIRA, BLIIRA

Intense green or blue light, the kind produced by frequency doubling, makes lithium niobate temporarily absorb infrared light (GRIIRA, BLIIRA). Electrons excited by the green light get stuck on niobium ions sitting in lithium sites, and each stuck electron (a bound small polaron) absorbs near-infrared photons. The absorbed infrared heats the crystal where the beams overlap, which detunes the phase matching and caps conversion efficiency. The magnesium doping that cures photorefraction removes the trap sites.

(A) Polaron absorption bands, Gaussian approximation, peak-normalizedNbLi bands scale with the NbLi fraction
0.51.01.52.02.53.03.5532 nm1064 nm1550 nmNb⁴⁺ on Li site, boundNb⁴⁺ on Nb site, freebipolaronO⁻ (no width tabulated)photon energy (eV)
Nb⁴⁺ on Li site, bound
1.60 eV, HWHM 0.40
Nb⁴⁺ on Nb site, free
1.00 eV, HWHM 0.37
bipolaron
2.50 eV, HWHM 0.55
O⁻ hole polaron
2.48 eV, n/a
532 / 1064 / 1550 nm
2.33 / 1.17 / 0.80 eV

Solid: NbLi4+; dashed: NbNb4+; thin: bipolaron. NbLi-related bands scale with the NbLi fraction (template, linear to zero at the threshold).

(B) GRIIRA chain, model parameters, no data template
Ig  2.50 kW/cm² → N/Nmax 0.551 → α1064 1.10e−02 /cm → ΔT  1.101 K → SHG rel. 0.731
 2.50 kW/cm²
0.00 %
10.0 W
Crystal
Eband 1.60 eV (775 nm)HWHM 0.40 eVthreshold 5.0 % MgSHG rel. 0.73∂Δk/∂T 173.4 rad/(m K)
band centres and widths Schwesyg 2011, Table 2.1P-comp thresholds 5% CLN, 1.5% NSLN P-comp dDk/dT: Jundt Sellmeier, Λ 6.78 µm at 25 °C derived no TFLN GRIIRA data found; bulk values

Green fills the traps, infrared pays

where green-induced infrared absorption comes from
1.60 eVNb⁴⁺ on Li site, bound1.00 eVNb⁴⁺ on Nb site, free2.50 eVbipolaron 0.5 eV1.0 eV1.5 eV2.0 eV2.5 eV3.0 eV3.5 eVNb⁴⁺ on Li site, boundNb⁴⁺ on Nb site, freebipolaron532 nm1064 nm1550 nm green 2.5 kW/cm²→polarons0.55 Nₘₐₓ→IR absorption0.0110 /cm→heating 1.10 K→SHG0.73
 2.50 kW/cm²
0.00 %
Crystal
10.0 W
Threshold for this crystal
5.0 % Mg
Bound polaron band
1.60 eV, 775 nm
SHG, relative
0.73
QPM detuning per kelvin
173.4 rad/(m K)

Wells: configuration-coordinate schematic, vertical arrow = optical transition at the tabulated band energy.

Push magnesium past the threshold: the 1.6 eV band vanishes and SHG returns to 1 (NbLi fraction: template, linear to zero at the threshold). Detuning slope from the Jundt Sellmeier, Λ 6.78 µm at 25 °C derived. No GRIIRA measurement in thin films was found; bulk values only.

bands Schwesyg 2011, Table 2.1P-compthresholds Volk & Wöhlecke 2009, p. 96P-compchain: model parameters, no data template1064 and 1550 nm: false color, dashed

L2 Bands and thresholds

Schwesyg Table 2.1; Volk & Wöhlecke pp. 14-19, 94-96
CenterAbsorption peakWidth (HWHM)Source
Bound small polaron NbLi4+12900 cm−1 (1.60 eV, 775 nm)3200 cm−1Schwesyg 2011, Table 2.1, p. 11P-comp
Free small polaron NbNb4+8050 cm−1 (about 1.0 eV); 0.95 eV in reduced above-threshold MgO:LN3000 cm−1Schwesyg 2011, p. 11P-comp Volk & Wöhlecke 2009, p. 19P-comp
Bound bipolaron NbLi4+-NbNb4+20140 cm−1 (2.50 eV)4400 cm−1Schwesyg 2011, p. 12P-comp
Bound hole polaron O− (near a Li vacancy)20000 cm−1 (500 nm), very broadnot tabulatedSchwesyg 2011, p. 12P-comp
Bipolaron dissociation energyabout 0.3 eVthermalVolk & Wöhlecke 2009, p. 17P-comp
Small-polaron hopping activation0.49 eV (optical 1.6 eV : thermal about 4:1)reduced LNVolk & Wöhlecke 2009, pp. 18-19P-comp
QuantityValueSource
GRIIRA assignmentsmall bound polaron on the Nb antisite, NbLi5+ + e− → NbLi4+Furukawa et al. 2001reported Volk & Wöhlecke 2009, p. 96P-comp
GRIIRA thresholdsame MgO threshold as photorefractionFurukawa et al. 2001reported
GRIIRA thresholds in Mgabout 5% (CLN), about 1.5% (NSLN)Volk & Wöhlecke 2009, p. 96 (data Furukawa 2001)P-comp
Measurement conditions532 nm pump at 2.5 kW/cm2, 1064 nm probe at 21 kW/cm2; decays practically instantly when the pump stops; photothermal techniqueVolk & Wöhlecke 2009, Fig. 4.14, p. 96P-comp Furukawa et al. 2001reported
Picosecond BLIIRAlowest in KNbO3 and MgO-doped congruent and stoichiometric LN; periodic poling slightly increases itHirohashi et al. 2007reported
Dark (gray) tracevisible absorption rises from 0.03 to 0.15-0.2 cm−1 after IR pulse exposure; transmission loss 10-15%; about 100 MW/cm2 with repeated pulsesVolk & Wöhlecke 2009, pp. 51, 94-95P-comp
Dark trace lifetimestable in CLN; decays in 10-20 min in Mg- or Zn-doped crystals above thresholdVolk & Wöhlecke 2009, pp. 95-96P-comp
Consequencelocal heating, thermal lens, disturbed phase matchingVolk & Wöhlecke 2009, p. 95P-comp

Band shape: Volk & Wöhlecke Eq. 2.11 gives the small-bound-polaron absorption as a Gaussian in photon energy around 4U + ε, fitted to the 1.6 eV band with phonon energy ℏω0 ≈ 0.1 eV and polaron stabilization energy U ≈ 0.3 eV (p. 18 P-comp).

L3 Band shapes and gaps

bulk data only
  • Bands are drawn as Gaussians in photon energy at the tabulated centres and HWHM; the O− band has no tabulated width and is drawn as a marker. Peak heights are normalized; relative strengths are not drawn.
  • Thin-film gap: no paper quantifying GRIIRA or BLIIRA in TFLN was found. Values on this page are bulk.
  • Polaron model reviews: Schirmer et al. 2009 reported (title) (electron small polarons and bipolarons), Imlau et al. 2015 reported (title) (optical nonlinearities of small polarons). Their numbers were not read; band values come from the two compilations above.
  • Measurement: photothermal (heating-induced phase change of a probe), pump-probe transmission at 1064 nm under 532 nm pumping, or calorimetry.
  • The trap that hosts the polaron is the Nb antisite that MgO replaces (4.2); the gray track and laser breakdown sit higher on the intensity ladder (4.5).

Sources

  1. Furukawa et al. 2001Y. Furukawa, K. Kitamura, A. Alexandrovski, R. K. Route, M. M. Fejer, G. Foulon, Green-induced infrared absorption in MgO doped LiNbO3. Applied Physics Letters 78 1970-1972 (2001), doi:10.1063/1.1359137.Read: abstract; data via Volk & Wöhlecke Table 4.3 and Fig. 4.14 (P-comp)
  2. Hirohashi et al. 2007J. Hirohashi, V. Pasiskevicius, S. Wang, F. Laurell, Picosecond blue-light-induced infrared absorption in single-domain and periodically poled ferroelectrics. Journal of Applied Physics 101 033105 (2007), doi:10.1063/1.2434007.Read: abstract
  3. Schirmer et al. 2009O. F. Schirmer, M. Imlau, C. Merschjann, B. Schoke, Electron small polarons and bipolarons in LiNbO3. Journal of Physics: Condensed Matter 21 123201 (2009), doi:10.1088/0953-8984/21/12/123201.Read: title
  4. Imlau et al. 2015M. Imlau, H. Badorreck, C. Merschjann, Optical nonlinearities of small polarons in lithium niobate. Applied Physics Reviews 2 040606 (2015), doi:10.1063/1.4931396.Read: title
  5. 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)
  6. Schwesyg 2011Judith R. M.-L. Schwesyg, Interaction of light with impurities in lithium niobate crystals. Dr. rer. nat. dissertation, Universität Bonn (2011).Read: selected: Sec. 2.2.2-2.3.2 (pp. 10-21), Ch. 5 Sec. 5.1 (pp. 69-72), Sec. 5.4-5.5 (pp. 99-101)