Browsing by Author "Fang, Jianxiong"

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    Beam pointing stabilization of an acousto-optic modulator with thermal control
    (OSA, 2019-04) Zhang, Xiao; Chen, Yang; Fang, Jianxiong; Wang, Tishuo; Li, Jiaming; Luo, Le; Physics, School of Science
    Diffraction beams generated by an acousto-optic modulator (AOM) are widely used in various optical experiments, some of which require high angular stability with the temporal modulation of optical power. Usually, it is difficult to realize both angular stability and high-power modulation in a passive setup without a servo system of radio-frequency compensation. Here, we present a method to suppress the angular drift and pointing noise only with the thermal management of the AOM crystal. We analyze the dependence of the angular drift on the refractive index variation and find that the angular drift is very sensitive to the temperature gradient, which could induce the refractive index gradient inside the AOM crystal. It reminds us that such angular drift could be significantly suppressed by carefully overlapping the zero temperature gradient area with the position of the acousto-optic interaction zone. We implement a water-cooling setup and find that the angular drift of an AOM is reduced over 100 times during the thermal transient and the angular noise is also suppressed to one-third of the non-cooled case. It should be emphasized that this thermal control method generally used to suppress the beam drift in both the diffraction and the perpendicular-to-diffraction directions. The refractive index thermal coefficient of tellurium dioxide crystal at 1064 nm determined by this angular drift-temperature model is 16×10 −6 K −1, consistent with previous studies. This thermal control technique provides potential applications for optical trapping and remote sensoring that demand for intensity ramps.
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    Observation of two PT transitions in an electric circuit with balanced gain and loss
    (Springer, 2020-08) Wang, Tishuo; Fang, Jianxiong; Xie, Zhongyi; Dong, Nenghao; Joglekar, Yogesh N.; Wang, Zixin; Li, Jiaming; Luo, Le; Physics, School of Science
    We investigate 𝓟𝓣-symmetry breaking transitions in a dimer comprising two LC oscillators, one with loss and the second with gain. The electric energy of this four-mode model oscillates between the two LC circuits, and between capacitive and inductive energy within each LC circuit. Its dynamics are described by a non-Hermitian, 𝓟𝓣-symmetric Hamiltonian with three different phases separated by two exceptional points. We systematically measure the eigenfrequencies of energy dynamics across the three regions as a function of gain-loss strength. In addition to observe the well-studied 𝓟𝓣 transition for oscillations across the two LC circuits, at higher gain-loss strength, transition within each LC circuit is also observed. With their extraordinary tuning ability, 𝓟𝓣-symmetric electronics are ideally suited for classical simulations of non-Hermitian systems.