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Studies on optical, electrical, mechanical and theoretical investigation of 4-nitro-benzoic acid (3-ethoxy-2-hydroxy-benzylidene)-hydrazide: A novel Schiff base organic NLO material
摘要： New organic non-centrosymmetric Schiff base material 4-Nitro-benzoic acid (3-ethoxy-2-hydroxy-benzylidene)-hydrazide was synthesized and grown as single crystal by slow evaporation solution growth technique. Single crystal X-ray diffraction reveals the noncentrosymmetric nature of the grown crystal with space group Pna21. The nonlinear efficiency of the grown material was studied by Kurtz-Perry powder technique and found to be 0.7 times that of KDP. The photoluminescence emission of the grown crystal shows emission at 360 nm. The mechanical stability of the crystal was examined by Vicker’s microhardness study and the yield strength of the material was calculated. Low dielectric constant at higher frequencies was observed from dielectric measurements. Reduction in charge carriers when the sample was illuminated by halogen lamp proves the negative photoconductivity of the sample. In addition, quantum chemical calculations were carried out using density functional theory for the NEH molecule optimized at B3LYP/6-31+G (d, p) basis set to calculate its frontier molecular orbital, Electrostatic potential and Mulliken charge analysis.
关键词： DFT,Dielectrics,Schiff base,non-centrosymmetric,Crystal growth
更新于2025-09-23 15:23:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Passively Mode-Locked Self-Frequency Doubling Yb:LGSB Laser
摘要： Non-centrosymmetric crystals exploited as host matrices for rare earth active ions simultaneously enable a self-frequency doubling (SFD) process. In case of ytterbium doping it allows to obtain laser radiation at 1 μm and its SFD signal covering green spectral range. This mechanism is particularly interesting in case of mode-locked oscillators as the intensity within the crystal is much higher, thus increasing the conversion efficiency. Moreover, it can be also employed for cascaded χ(2) processes. Nevertheless, despite more than 20 years of development of Yb-doped mode-locked bulk lasers there are very few demonstrations of femtosecond oscillators with SFD properties [1-3]. One of the recently introduced non-centrosymmetric Yb3+-doped active media is LaxGdyYbzScw(BO3)4 (x + y + z + w = 4; shortly Yb:LGSB) crystal [4,5]. This novel scandium borate compound is a negative uniaxial crystal and it exhibits strong second order nonlinearity (point group 32). The nonlinear coefficient d11 amounts to 2.1 pm/V, which is much higher than in case of previously investigated SFD crystals [1-3]. Moreover, its emission spectrum is relatively broad and thus it is a very promising candidate for femtosecond SFD, which, to the best of our knowledge, has never been demonstrated with this gain medium before. Here, we demonstrate the first mode-locked operation of a laser based on an Yb:LGSB gain medium. The scheme of the X-shaped resonator cavity is depicted in Fig. 1a. An investigated c-cut 2.55 mm-long La0.681Gd0.308Yb0.129Sc2.882(BO3)4. crystal was grown by Czochralski method [4]. It was pumped by a 1 W fiber-coupled single-mode laser diode with central wavelength of 979 nm. Due to lack of the AR-coatings it was inclined under Brewster’s angle. As a saturable absorber we used a semiconductor saturable absorber mirror (SESAM) with 0.6% modulation depth and 10 ps relaxation time. In order to obtain stable soliton mode-locked operation the anomalous dispersion of -1650 fs2 was introduced to the cavity by the Gires-Tournois-interferometer (GTI) mirrors. The output coupler transmission was 0.8%. In this configuration the laser emitted 6.8 nm broad spectrum centered at 1070 nm (Fig. 1b), which corresponds to transform-limited pulse duration of 180 fs. The output average power was equal to 32 mW with repetition rate of 89 MHz. During mode-locked operation we could also observe a self-frequency doubled signal. Due to the low reflectivity of the employed mirrors in the green, the strongest SFD signal was detected after one of folding mirrors. The second harmonic spectrum is shown in the inset of the Fig. 1b. The fringes originate from the fact that SFD was not phase-matched in this case [3]. The work was supported by National Science Centre (NCN, Poland; grant 2015/18/E/ST7/00296) and by Ministry of Research and Innovation of Romania (CNCS-UEFISCDI, grant PN-III-P4-ID-PCE-2016-0853 within PNCDI III).
关键词： Yb:LGSB,mode-locked laser,non-centrosymmetric crystals,femtosecond oscillator,self-frequency doubling
更新于2025-09-12 10:27:22