Comparison of photorefractive effects in undoped and MgO-doped PPLN
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Bibliographic record
Abstract
Quasi-phase-matched (QPM) wavelength conversions based on the second-order nonlinear interaction, such as second-harmonic generation (SHG), difference-frequency generation (DFG) and sum-frequency generation (SFG), in periodically poled lithium niobate (PPLN)) have attracted much attention due to their excellent conversion properties such as broad bandwidth, high efficiency, and low noise. To achieve an efficient conversion, high-power pump light is always desired. However, PPLN crystals (either bulk or waveguide) are somehow vulnerable to high-power irradiating light, especially at a short wavelength due to the photorefractive effect (PRE), known as a refractive index change induced by an intense light illumination. The PRE may deteriorate device performance significantly. To suppress the PRE, PPLN crystals usually have to be operated at high temperatures (over one hundred degrees Celsius) or to be specially doped. Despite the significant impacts of the PRE on device performance, to date, there is limited information in the literature on the PRE mechanism in QPM PPLN. In this work, we adopt the pump-probe method and characterize the PRE in undoped and 5-mol% MgO-doped PPLN crystals. Especially, we compare the PRE in bulk and annealed proton-exchanged (APE) waveguides of PPLN. A broadband light source at 1.55 &mgr;m was used as the probe, and narrowband light at two wavelengths of 0.5 and 1.1 &mgr;m was alternatively taken as the pump. The period of crystals were selected to meet the QPM condition of SHG. It is shown that the decay property and temperature dependence of PRE, the wavelength and amplitude changes of the SHG tuning curve are distinct for the undoped and MgO-doped PPLN, as well as for the bulk and waveguide, which implies a few competing interactions in the crystals, such as the PRE, thermal-optic, photogalvanic and two-photon absorption effect, etc.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it