Inline self-diffraction dispersion-scan of over octave-spanning pulses in the single-cycle regime

We present an implementation of dispersion-scan based on self-diffraction (SD d-scan) and apply it to the measurement of over octave-spanning sub-4-fs pulses. The results are compared with second-harmonic generation (SHG) d-scan. The efficiency of the SD process is derived theoretically and compared with the spectral response retrieved by the d-scan algorithm. The new SD d-scan has a robust inline setup and enables measuring pulses with over-octave spectra, single-cycle durations and wavelength ranges beyond those of SHG crystals, such as the ultraviolet and the deep-ultraviolet.Comment: 8 pages, 5 figure

Effective lagrangian for a mass dimension one fermionic field in curved spacetime

In this work we use momentum-space techniques to evaluate the propagator $G(x,x^{\prime})$ for a spin $1/2$ mass dimension one spinor field on a curved Friedmann-Robertson-Walker spacetime. As a consequence, we built the one-loop correction to the effective lagrangian in the coincidence limit. Going further we compute the effective lagrangian in the finite temperature regime. We arrive at interesting cosmological consequences, as time-dependent cosmological `constant', fully explaining the functional form of previous cosmological models.Comment: 9 pages, 0 figure

New Algorithms for Computing a Single Component of the Discrete Fourier Transform

This paper introduces the theory and hardware implementation of two new algorithms for computing a single component of the discrete Fourier transform. In terms of multiplicative complexity, both algorithms are more efficient, in general, than the well known Goertzel Algorithm.Comment: 4 pages, 3 figures, 1 table. In: 10th International Symposium on Communication Theory and Applications, Ambleside, U

Non-white frequency noise in spin torque oscillators and its effect on spectral linewidth

We measure the power spectral density of frequency fluctuations in nanocontact spin torque oscillators over time scales up to 50 ms. We use a mixer to convert oscillator signals ranging from 10 GHz to 40 GHz into a band near 70 MHz before digitizing the time domain waveform. We analyze the waveform using both zero crossing time stamps and a sliding Fourier transform, discuss the different limitations and advantages of these two methods, and combine them to obtain a frequency noise spectrum spanning more than five decades of Fourier frequency $f$. For devices having a free layer consisting of either a single Ni$_{\text{}80}$Fe$_{\text{}20}$ layer or a Co/Ni multilayer we find a frequency noise spectrum that is white at large $f$ and varies as \emph{$1/f$} at small $f$. The crossover frequency ranges from \approx\unit[10^{4}]{Hz} to \approx\unit[10^{6}]{Hz} and the $1/f$ component is stronger in the multilayer devices. Through actual and simulated spectrum analyzer measurements, we show that $1/f$ frequency noise causes both broadening and a change in shape of the oscillator's spectral line as measurement time increases. Our results indicate that the long term stability of spin torque oscillators cannot be accurately predicted from models based on thermal (white) noise sources

The Low Energy Limit of the Chern-Simons Theory Coupled to Fermions

We study the nonrelativistic limit of the theory of a quantum Chern--Simons field minimally coupled to Dirac fermions. To get the nonrelativistic effective Lagrangian one has to incorporate vacuum polarization and anomalous magnetic moment effects. Besides that, an unsuspected quartic fermionic interaction may also be induced. As a by product, the method we use to calculate loop diagrams, separating low and high loop momenta contributions, allows to identify how a quantum nonrelativistic theory nests in a relativistic one.Comment: 18 pages, 8 figures, Late