Appl. Sci.2014, 4(4), 515-524; doi:10.3390/app4040515 (registering DOI) - published 26 November 2014 Show/Hide Abstract
Abstract: We report a multi-watt broadband continuous-wave multi-harmonic optical comb based on a frequency division-by-three singly-resonant optical parametric oscillator. This cw optical comb is frequency-stabilized with the help of a beat signal derived from the signal and frequency-doubled idler waves. The measured frequency fluctuation in one standard deviation is ~437 kHz. This is comparable to the linewidth of the pump laser which is a master-oscillator seeded Yb:doped fiber amplifier at ~1064 nm. The measured powers of the fundamental wave and the harmonic waves up to the 6th harmonic wave are 1.64 W, 0.77 W, 3.9 W, 0.78 W, 0.17 W, and 0.11 W, respectively. The total spectral width covered by this multi-harmonic comb is ~470 THz. When properly phased, this multi-harmonic optical comb can be expected to produce by Fourier synthesis a light source consisting of periodic optical field waveforms that have an envelope full-width at half-maximum of 1.59 fs in each period.
Appl. Sci.2014, 4(4), 498-514; doi:10.3390/app4040498 - published 18 November 2014 Show/Hide Abstract
Abstract: We demonstrate an optical modulator at a frequency of 90 THz that has the capability to modulate any laser beam in the optical region of the spectrum. The modulator is constructed by placing deuterium molecules inside a high-finesse cavity and driving a vibrational transition with two continuous-wave laser beams. The two beams, the pump and the Stokes, are resonant with the cavity. The high intra-cavity intensities that build up drive the molecules to a coherent state. This molecular coherence can then be used to modulate an independent laser beam, to produce frequency up-shifted and down-shifted sidebands. The beam to be modulated is not resonant with the cavity and thus the sidebands are produced in a single pass.
Appl. Sci.2014, 4(4), 482-492; doi:10.3390/app4040482 - published 29 September 2014 Show/Hide Abstract
Abstract: Network transformations are the techniques to obtain new functional schemes from available circuits. They are systematic methodologies, since each transformation technique can be applied to many circuits to obtain the desired functions or characteristics. A convenient network transformation method, exploiting different circuit transformations, for deriving linear sinusoidal oscillators from biquadratic band pass filters is proposed. This method with generality can be applied to any band pass filter. The oscillation frequency of the new obtained oscillator is identical to the center frequency of the original band pass filter, and the useful properties of the selected band pass filter can be retained. Two examples are illustrated to confirm the feasibility of the proposed approach. The workability of the obtained oscillators is verified with PSPICE simulations.
Appl. Sci.2014, 4(3), 468-481; doi:10.3390/app4030468 - published 22 September 2014 Show/Hide Abstract
Abstract: The effect of the calcination conditions on the catalytic activity for N2O decomposition of 2.5% RhOx/CeO2 catalysts has been investigated. Ramp and flash calcinations have been studied (starting calcinations at 25 or 250/350 °C, respectively) both for cerium nitrate and ceria-impregnated rhodium nitrate decomposition. The cerium nitrate calcination ramp has neither an effect on the physico-chemical properties of ceria, observed by XRD, Raman spectroscopy and N2 adsorption, nor an effect on the catalysts performance for N2O decomposition. On the contrary, flash calcination of rhodium nitrate improved the catalytic activity for N2O decomposition. This is attributed to the smaller size of RhOx nanoparticles obtained (smaller than 1 nm) which allow a higher rhodium oxide-ceria interface, favoring the reducibility of the ceria surface and stabilizing the RhOx species under reaction conditions.
Appl. Sci.2014, 4(3), 444-467; doi:10.3390/app4030444 - published 22 September 2014 Show/Hide Abstract
Abstract: This paper introduces and discusses the main aspects of multicolored femtosecond pulse generation using cascaded four-wave mixing (CFWM) in transparent bulk materials. Theoretical analysis and semi-quantitative calculations, based on the phase-matching condition of the four-wave mixing process, explain the phenomena well. Experimental studies, based on our experiments, have shown the main characteristics of the multicolored pulses, namely, broadband spectra with wide tunability, high stability, short pulse duration and relatively high pulse energy. Two-dimensional multicolored array generation in various materials are also introduced and discussed.