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- ItemTemperature-Dependent Reinforcement of Hydrophilic Rubber Using Ice Crystals(Washington, DC : ACS Publications, 2017-2-2) Natarajan, Tamil Selvan; Stöckelhuber, Klaus Werner; Malanin, Mikhail; Eichhorn, Klaus-Jochen; Formanek, Petr; Reuter, Uta; Wießner, Sven; Heinrich, Gert; Das, AmitThis is the first study on the impact of ice crystals on glass transition and mechanical behavior of soft cross-linked elastomers. A hydrophilic elastomer such as epichlorohydrin-ethylene oxide-allyl glycidyl ether can absorb about ∼40 wt % of water. The water-swollen cross-linked network exhibits elastic properties with more than 1500% stretchability at room temperature. Coincidently, the phase transition of water into solid ice crystals inside of the composites allows the reinforcement of the soft elastomer mechanically at lower temperatures. Young's modulus of the composites measured at -20 °C remarkably increased from 1.45 to 3.14 MPa, whereas at +20 °C, the effect was opposite and the Young's modulus decreased from 0.6 to 0.03 MPa after 20 days of water treatment. It was found that a part of the absorbed water, ∼74% of the total absorbed water, is freezable and occupies nearly 26 vol % of the composites. Simultaneously, these solid ice crystals are found to be acting as a reinforcing filler at lower temperatures. The size of these ice crystals is distributed in a relatively narrow range of 400-600 nm. The storage modulus (E′) of the ice crystal-filled composites increased from 3 to 13 MPa at -20 °C. The glass transition temperature (-37 °C) of the soft cross-linked elastomer was not altered by the absorption of water. However, a special transition (melting of ice) occurred at temperatures close to 0 °C as observed in the dynamic mechanical analysis of the water-swollen elastomers. The direct polymer/filler (ice crystals) interaction was demonstrated by strain sweep experiments and investigated using Fourier transform infrared spectroscopy. This type of cross-linked rubber could be integrated into a smart rubber application such as in adaptable mechanics, where the stiffness of the rubber can be altered as a function of temperature without affecting the mechanical stretchability either below or above 0 °C (above the glass temperature region) of the rubber.
- ItemWedged Nd:YVO4 crystal for wavelength tuning of monolithic passively Q-switched picosecond microchip lasers(Washington, DC : Soc., 2021) Marianovich, André; Spiekermann, Stefan; Brendel, Moritz; Wessels, Peter; Neumann, Jörg; Weyers, Markus; Kracht, DietmarWe present a monolithic integrated passively Q-switched sub-150 ps microchip laser at 1064 nm with a wedged Nd:YVO4 crystal operating up to a repetition rate of 1 MHz. The wedge enables to change the cavity length by a small amount to fine tune the spectral cavity mode position over the full gain bandwidth of Nd:YVO4 and hence to optimize the output power. This additional degree of freedom may be a suitable approach to increase the wafer scale mass production yield or also to simplify frequency tuning of CW single-frequency microchip lasers.
- ItemHigh-temperature electromechanical loss in piezoelectric langasite and catangasite crystals(Melville, NY : American Inst. of Physics, 2021) Suhak, Yuriy; Fritze, Holger; Sotnikov, Andrei; Schmidt, Hagen; Johnson, Ward L.Temperature-dependent acoustic loss Q−1 is studied in partially disordered langasite (LGS, La3Ga5SiO14) and ordered catangasite (CTGS, Ca3TaGa3Si2O14) crystals and compared with previously reported CTGS and langatate (LGT, La3Ga5.5Ta0.5O14) data. Two independent techniques, a contactless tone-burst excitation technique and contacting resonant piezoelectric spectroscopy, are used in this study. Contributions to the measured Q−1(T) are determined through fitting to physics-based functions, and the extracted fit parameters, including the activation energies of the processes, are discussed. It is shown that losses in LGS and CTGS are caused by a superposition of several mechanisms, including intrinsic phonon–phonon loss, point-defect relaxations, and conductivity-related relaxations.
- ItemTm3+-doped calcium lithium tantalum gallium garnet (Tm:CLTGG): novel laser crystal(Washington, DC : OSA, 2021) Alles, Adrian; Pan, Zhongben; Loiko, Pavel; Serres, Josep Maria; Slimi, Sami; Yingming, Shawuti; Tang, Kaiyang; Wang, Yicheng; Zhao, Yongguang; Dunina, Elena; Kornienko, Alexey; Camy, Patrice; Chen, Weidong; Wang, Li; Griebner, Uwe; Petrov, Valentin; Solé, Rosa Maria; Aguiló, Magdalena; Díaz, Francesc; Mateos, XavierWe report on the development of a novel laser crystal with broadband emission properties at ∼2 µm – a Tm3+,Li+-codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr. 𝐼𝑎3¯𝑑, a = 12.5158(0) Å) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm-1K-1. Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li+ codoping. The transition probabilities of Tm3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Ω2 = 5.185, Ω4 = 0.650, Ω6 = 1.068 [10−20 cm2] and α = 0.171 [10−4 cm]. The crystal-field splitting of the Tm3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at ∼2 µm with a slope efficiency of 23.8%. The Tm3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta5+ and Ga3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 µm and rendering Tm:CLTGG suitable for femtosecond pulse generation.
- ItemDiode-pumped sub-50-fs Kerr-lens mode-locked Yb:GdYCOB laser(Washington, DC : Soc., 2021) Zeng, Huangjun; Lin, Haifeng; Lin, Zhanglang; Zhang, Lizhen; Lin, Zhoubin; Zhang, Ge; Petrov, Valentin; Loiko, Pavel; Mateos, Xavier; Wang, Li; Chen, WeidongWe present a sub-50-fs diode-pumped Kerr-lens mode-locked laser employing a novel “mixed” monoclinic Yb:Ca4(Gd,Y)O(BO3)3 (Yb:GdYCOB) crystal as a gain medium. Nearly Fourier-limited pulses as short as 43 fs at 1036.7 nm are generated with an average power of 84 mW corresponding to a pulse repetition rate of ∼70.8 MHz. A higher average power of 300 mW was achieved at the expense of the pulse duration (113 fs) corresponding to an optical-to-optical efficiency of 35.8% representing a record-high value for any Yb-doped borate crystal. Non-phase-matched self-frequency doubling is observed in the mode-locked regime with pronounced strong spectral fringes which originate from two delayed green replicas of the fundamental femtosecond pulses in the time domain.