PE-Layers and Proton Diffusion Profiles in LiNbO3 Investigated with Fourier-IR and Second Harmonic Generation

Abstract

Deep proton‐exchanged (PE) layers in congruent LiNbO3 with thickness up to 10 μm are studied by Fourier‐IR spectroscopy, mode‐coupling, and interference techniques. Effective diffusion constants, depending on the amount of Li buffering in the benzoic melt and crystal cut, as well as the relation between layer thickness and the absorption of the fundamental (v01) and the next higher O‐H vibrational transition (v02) are measured. Based upon the H/Li exchange ratio in the layer an OH oscillator strength for v01 offosc = 1.6 × 10−2 is found. This allows to determine the refractive index change per OH concentration by combining frequency doubling (SHG) and absorption measurements in OH profiles in the bulk of LiNbO3. Resulting values for H indiffusion Δne/ΔCH = (2.9 ± 0.6) × 10−23 cm3 and Li outdiffusion Δne/ΔCli = 3.4 × 10−23 cm3 are about the same. Extrapolation of these Δn values to the large [H]/[Li] variation in the PE‐layer, leads to much larger Δn values than observed, pointing to a strongly nonlinear mechanism.

On the quantification of hydrogen in lithium metal oxides

“…In accordance with the A / c H value, the oscillator strength of LiNbO 3 is ∼36% higher than that in LiTaO 3 , which leads to the observation of a stronger IR absorption in the LiNbO 3 host lattice by the transition between the energy levels of the OH − molecule, even if the underlying H concentration is slightly lower. The determined f OH values are comparable to earlier data of PE-LiNbO 3 with 1.6 × 10 −2 151 and 1.7 × 10 −2 , 68 where both publications used the same [H]/[Li] exchange rate from SIMS measurements to estimate the H concentration. Comparable values are also found for other oxides, such as for the O–H oscillator in TiO 2 with 3.8 × 10 −2 26 or the O–D oscillator in MgO with 2 × 10 −2 .…”

“…The studies on the PE-LiNbO 3 crystals 67,68,151 show much higher σ values than other literature data, but considering the A / c H value these studies are very comparable to our calibration value of LiNbO 3 . These studies do not use a direct measurement of the hydrogen concentration, but the assumption that the PE reaction is a one-to-one exchange of Li + → H + and about 70–75% of the lithium is replaced on the first 2–3 μm.…”

Ultraslow Shock Waves of Electron Density inLiNbO3Crystals

“…Using the technique of infrared absorption at 2870 nm [16,17], we have detected an increase of the concentration of H þ ions up to %10 19 cm À3 near the anode. Quantitatively, taking into account the spatially nonuniform H þ contribution to the conductivity goes beyond the scope of this Letter.…”

Ionic and electronic dark decay of holograms in LiNbO3:Fe crystals

“…15 The crystals were placed on a heatable plate whose temperature was controlled within 0.1°C accuracy. An argon-ion laser beam with a wavelength of 514 nm was used in all of the experiments to record the holograms.…”