Frequency multiplier

Abstract: We have used the frequency comb generated by a femtosecond mode-locked laser and broadened to more than an optical octave in a photonic crystal fiber to realize a frequency chain that links a 10 MHz radio frequency reference phase-coherently in one step to the optical region. By comparison with a similar frequency chain we set an upper limit for the uncertainty of this new approach to 5. 1x10(-16). This opens the door for measurement and synthesis of virtually any optical frequency and is ready to revolutionize frequency metrology.

Abstract: A radio frequency generator for an electrosurgical system is provided, the system including an electrode assembly having two electrodes for use immersed in an electrically conductive fluid. The generator has control circuitry for rapidly reducing the delivered radio frequency output power by at least 50 % within at most a few cycles of the peak radio frequency output voltage reaching a predetermined threshold limit. In this way, tissue coagulation can be performed in, for example, saline without significant steam generation. The same peak voltage limitation technique is used in a tissue vaporisation or cutting mode to limit the size of the steam pocket at the electrodes and to avoid electrode burning. The generator has a push-pull output stage with a series-resonant output circuit, the output stage being driven by a radio frequency oscillator at a frequency which, in general, differs from the resonant frequency of the resonant output circuit. Power control is achieved by varying the ON-time of switching transistors forming the push-pull output pair and by altering the frequency spacing between the excitation frequency and the resonant frequency of the series-resonant output circuit. In an alternative embodiment, a bridge configuration using two push-pull pairs is used, yielding a further power control variable: the relative phase of the driving signals to the respective transistor pairs.

Abstract: Graphene is a recently discovered carbon-based material with unique physical properties. This is a monolayer of graphite, and the two-dimensional electrons and holes in it are described by the effective Dirac equation with a vanishing effective mass. As a consequence, the electromagnetic response of graphene is predicted to be strongly nonlinear. We develop a quasi-classical kinetic theory of the nonlinear electromagnetic response of graphene, taking into account the self-consistent-field effects. The response of the system to both harmonic and pulse excitation is considered. The frequency multiplication effect, resulting from the nonlinearity of the electromagnetic response, is studied under realistic experimental conditions. The frequency upconversion efficiency is analyzed as a function of the applied electric field and parameters of the samples. Possible applications of graphene in terahertz electronics are discussed.

Abstract: Two circuits for use to control the frequency of a microwave oscillator by an external high Q cavity are described. One of the circuits uses a microwave equivalent of the frequency discriminator, in conjunction with a d.c. amplifier. The other uses the cavity in a special circuit that provides an intermediate‐frequency signal that is a measure of the difference between the frequencies of the oscillator and cavity. This allows the use of an intermediate‐frequency amplifier. The resulting stability of the oscillators is such that audible beat frequencies can be produced between two oscillators at 10,000 Mc/sec. The resultant signal can be frequency modulated at audiofrequencies, with stabilization acting throughout the modulation cycle. A technique by which the frequency‐stabilization systems could be used to investigate, with high resolution, the structure of microwave absorption spectra is suggested.