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Kim, Jungwon,Kä,rtner, Franz X Optical Society of America 2010 Optics letters Vol.35 No.12
<P>We present a feedback-control method for suppression of excess phase noise in the optical-to-electronic conversion process involved in the extraction of microwave signals from femtosecond mode-locked lasers. A delay-locked loop based on drift-free phase detection with a differentially biased Sagnac loop is employed to eliminate low-frequency (e.g., <1 kHz) excess phase noise and drift in the regenerated microwave signals. A 10 GHz microwave signal is extracted from a 200 MHz repetition rate mode-locked laser with a relative rms timing jitter of 2.4 fs (integrated from 1 mHz to 1 MHz) and a relative rms timing drift of 0.84 fs (integrated over 8 h with 1 Hz bandwidth) between the optical pulse train and the extracted microwave signal.</P>
Complete characterization of quantum-limited timing jitter in passively mode-locked fiber lasers.
Cox, Jonathan A,Nejadmalayeri, Amir H,Kim, Jungwon,Kä,rtner, Franz X Optical Society of America 2010 Optics letters Vol.35 No.20
<P>We characterize the timing jitter of passively mode-locked, femtosecond, erbium fiber lasers with unprecedented resolution, enabling the observation of quantum-origin timing jitter up to the Nyquist frequency. For a pair of nearly identical 79.4MHz dispersion-managed lasers with an output pulse energy of 450pJ, the high-frequency jitter was found to be 2.6fs [10kHz, 39.7MHz]. The results agree well with theoretical noise models over more than three decades, extending to the Nyquist frequency. It is also found that unexpected noise may occur if care is not taken in optimizing the mode-locked state.</P>
Park, Min Hyuk,Schenk, Tony,Hoffmann, Michael,Knebel, Steve,Gä,rtner, Jan,Mikolajick, Thomas,Schroeder, Uwe Elsevier 2017 Nano energy Vol.36 No.-
<P><B>Abstract</B></P> <P>Fluorite structured HfO<SUB>2</SUB> or ZrO<SUB>2</SUB> thin films have been intensively studied for memory- and energy-related applications since their ferroelectricity was first reported in 2011. The phase transition between the nonpolar tetragonal and the polar orthorhombic phase in these new ferroelectric materials is believed to be promising for energy harvesting, energy storage and solid state cooling. The temperature dependent phase transition and resulting strong pyroelectric and electrocaloric effect have been reported for Si-doped HfO<SUB>2</SUB> and (Hf,Zr)O<SUB>2</SUB> thin films. In this study, the effect of acceptor (Al and Gd) doping into HfO<SUB>2</SUB> thin films on their temperature dependent phase transition was systematically examined. The phase transitions in Al- and Gd-doped HfO<SUB>2</SUB> thin films were much broader compared to Si-doped HfO<SUB>2</SUB> and (Hf,Zr)O<SUB>2</SUB> films. The maximum adiabatic temperature change (ΔT) values of Al- and Gd-doped HfO<SUB>2</SUB> film were 5.7 and 3.1K, respectively. A giant negative electrocaloric effect with ΔT of −7.4K could be observed for Al-doped HfO<SUB>2</SUB>. The various factors which can potentially affect the phase transitions of HfO<SUB>2</SUB> films, such as dopant size, grain size distribution, spatial dopant distribution, and oxygen vacancy distribution were carefully examined to understand the different phase transition behavior. From the various factors, the distribution of oxygen vacancies is suggested as the origin of the different phase transitions of HfO<SUB>2</SUB> films doped with trivalent and tetravalent dopants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Phase transition of Al- and Gd-doped HfO<SUB>2</SUB> films are reported for the first time. </LI> <LI> The effect of acceptor doping on the phase transition of fluorite ferroelectrics is investigated in depth. </LI> <LI> The energy harvesting and storage as well as electrocaloric effect of Al- and Gd-doped HfO<SUB>2</SUB> thin films is examined and compared to other materials. </LI> </UL> </P> <P><B>Graphic abstract</B></P> <P>[DISPLAY OMISSION]</P>