Browsing by Subject "Individual cells"

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    Fiber laser-microscope system for femtosecond photodisruption of biological samples
    (Optical Society of America, 2012-02-22) Yavaş, Seydi; Erdoğan, Mutlu; Gürel, Kutan; İlday, F. Ömer; Eldeniz, Y. B.; Tazebay, Uygar H.
    We report on the development of a ultrafast fiber lasermicroscope system for femtosecond photodisruption of biological targets. A mode-locked Yb-fiber laser oscillator generates few-nJ pulses at 32.7 MHz repetition rate, amplified up to ~125 nJ at 1030 nm. Following dechirping in a grating compressor, ~240 fs-long pulses are delivered to the sample through a diffraction-limited microscope, which allows real-time imaging and control. The laser can generate arbitrary pulse patterns, formed by two acousto-optic modulators (AOM) controlled by a custom-developed fieldprogrammable gate array (FPGA) controller. This capability opens the route to fine optimization of the ablation processes and management of thermal effects. Sample position, exposure time and imaging are all computerized. The capability of the system to perform femtosecond photodisruption is demonstrated through experiments on tissue and individual cells.
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    Resonances and nonuniformities in CMUT elements or arrays
    (IEEE, 2014-09) Atalar, Abdullah; Köymen, Hayrettin
    We determine the response of individual cells of a CMUT array immersed in water using the small-signal equivalent circuit of a single cell and radiation impedances. Using a numerically efficient technique, we are able to simulate large arrays. The results indicate the presence of resonances at low frequencies where Rayleigh-Bloch waves are excited on the surface of the array. Reflections from the edges cause standing-wave patterns. Above the cut-off frequency of Rayleigh-Bloch waves, no standing-wave pattern exists. However, there is nonuniformity among cell velocities mainly due to unequal radiation impedance seen by the cells. Rayleigh-Bloch waves and nonuniformity in cell velocities do not cause a significant degradation in the point spread function, but the oscillations extend the duration of impulse response, limiting the dynamic range. © 2014 IEEE.