PROCEEDINGS ARTICLE | February 24, 2009
Proc. SPIE. 7197, Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications VIII
KEYWORDS: Lithium niobate, Femtosecond phenomena, Scattering, Crystals, Electrons, Light scattering, Laser scattering, Laser crystals, Photorefraction
The photorefractive effect in iron-doped lithium niobate crystals is investigated, using femtosecond pulses and
cw light, both at a wavelength of 532 nm, in direct comparison. For that purpose, measurements about "light-induced"
or "holographic" scattering of a single beam as well as writing of index gratings with two interfering
beams are performed.
We find that light-induced scattering is reduced for femtosecond pulses, and even absent for a sufficiently low
Fe<sup>2+</sup> concentration, in comparison and in contrast to cw light. Additional differences include a slower buildup
time and a weaker angular selectivity for the scattering of pulses. Our observations can be attributed to the
smaller temporal coherence of the pulses.
When writing index gratings into as-grown lithium niobate crystals, the saturation value of the refractive
index unexpectedly decreases with increasing pulse energy fluence. Furthermore, in oxidized crystals, writing
with femtosecond pulses turns out to be much faster than with cw light. A model about the charge excitation,
migration and trapping is proposed that explains these differences.
