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Parametric infrared generation : from crystals to devices

Abstract : This dissertation deals with the generation of parametric light in the range 1 to 12 µm. Parametric infrared generation turns out to be a challenge at the interface between the fields of nonlinear optics and materials science embodied by the two approaches used to achieve efficient frequency conversion. Birefringent Phase-Matching (BPM) in anisotropic materials has been the traditional solution used in most frequency converter devices. But since the 90's, the quick success of microstructured materials has paved the way for Quasi-Phase-Matching (QPM) even in isotropic materials, leading to a renewed interest in Optical Parametric Oscillators (OPO). The high degree of engineering offered by this technology is now widely recognized as a key competitive advantage. We obtained original results concerning parametric infrared generation using BPM as well as QPM.We have built the first OPO pumped by a 1.064 µm Nd:YAG laser and based on a 5-mm-thick crystal of 5%MgO:PPLN cut as a partial cylinder. This OPO combines a wide and continuous tunability over the range 1.4 µm - 4.4 µm with a good conversion efficiency, up to 30%. Despite the need to resort to pump intensities almost an order of magnitude higher than in a slab OPO, we have shown that the energetical performance of a partial cylinder OPO is now equivalent to that of a slab OPO besides a wider tunability that can be continuously addressed. When the same Nd:YAG laser pumps two such independent OPOs in parallel, we dispose of a highly versatile QPM dual wavelength source with two widely and independently tunable beams. We have built this unique source allowing versatile Difference Frequency Generation (DFG) towards the mid- and far- infrared. We carried out the first BPM DFG experiments with this source in a CdSe slab oriented for angular noncritical phase-matching at two different pump wavelengths, respectively 2.72 µm and 2.79 µm. The second set of DFG experiments were performed in a CdSe crystal cut and polished as a 5-mm-diameter full cylinder. Using a pump wavelength of 2.79 µm, we were able to tune the DFG wavelength from 8.3 µm up to 10.3 µm by rotating the crystal over an angular range of 18°. Contrary to all the BPM DFG experiments reported so far in the single crystal CdSe, tuning was achieved while keeping normal incidence of both the incident and generated beams in the crystal. The implementation of spectral narrowing techniques is already anticipated and will contribute to more accurate measurements of the phase-matching directions of a crystal as well as to a higher DFG conversion efficiency.These experiments with our dual wavelength source are preliminary and encouraging validations of our capability of performing DFG in small crystals and at any pump wavelength between 1.4 µm and 3.5 µm. Even though we investigated the promises held by CdSiP2 when it is only pumped with a Nd:YAG laser at 1.064 µm, there is tremendous prospect in terms of tunable infrared generation between 3.5 µm and 8 µm when this crystal is pumped around 2.4 µm. Such early demonstrations will be highly valuable for future applications requiring compact and tunable sources spanning the infrared spectrum. From a more fundamental point of view, performing DFG experiments at different pump wavelengths in the mid-infrared can lead to a highly accurate determination of the values of the refractive indices of a nonlinear crystal. In this dissertation, we have cast the first stone of a method that leads to the determination of the values of the refractive indices of a nonlinear crystal in the mid- to far- infrared. This new method is based on the unique measurements of the DFG phase-matching angles in spheres or cylinders, and should contribute to further advances in the field of phase-matching metrology.
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  • HAL Id : tel-03209194, version 2

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Vincent Kemlin. Parametric infrared generation : from crystals to devices. Optics [physics.optics]. Université de Grenoble, 2013. English. ⟨NNT : 2013GRENT114⟩. ⟨tel-03209194v2⟩

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