Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.

Phase control of absorption in large polyatomic molecules

Abstract: The phenomenon of interference of the amplitude for absorption of one photon of frequency 3ω and the amplitude for absorption of three photons of frequency ω was theoretically predicted by Shapiro, Hepburn, and Brumer. The interference was demonstrated experimentally by varying the relative phase between the tripled frequency photon and three photons with the fundamental frequency by the groups of Elliott and Gordon in atoms and small molecules. In order to see how general this phenomenon is, five compounds were studied, ammonia, trimethylamine, triethylamine, cyclooctatetraene, and 1,1‐dimethylhydrazine. CH3I was used as the tripling gas for light in the range 604–600 nm. Interference was observed in all cases. The last four compounds have low ionization potentials and interference was observed between a 3+1 and a 1+1 ionization process with a maximum modulation of 22%. NH3 with a higher ionization potential requires absorption of 3+2 or 1+2 photons and exhibits a maximum modulation of 33%. We conclude that molecular size is no obstacle and that as long as a molecule has sufficiently strong absorption at the tripled frequency, and sufficient vapor pressure, and the laser fundamental beam is very strong, phase control of interference is observable.

Asymmetric Gaussian harmonic steering in second-harmonic generation

Abstract: Intracavity second-harmonic generation is one of the simplest of the quantum optical processes and is well within the expertise of most optical laboratories. It is well understood and characterized, both theoretically and experimentally. We show that it can be a source of continuous-variable asymmetric Gaussian harmonic steering with fields which have a coherent excitation, hence combining the important effects of harmonic entanglement and asymmetric steering in one easily controllable device, adjustable by the simple means of tuning the cavity loss rates at the fundamental and harmonic frequencies. We find that whether quantum steering is available via the standard measurements of the Einstein-Podolsky-Rosen correlations can depend on which quadrature measurements are inferred from output spectral measurements of the fundamental and the harmonic. Altering the ratios of the cavity loss rates can be used to tune the regions where symmetric steering is available, with the results becoming asymmetric over all frequencies as the cavity damping at the fundamental frequency becomes significantly greater than at the harmonic. This asymmetry and its functional dependence on frequency is a potential new tool for experimental quantum information science, with possible utility for quantum key distribution. Although we show the effect here for Gaussian measurements of the quadratures, and cannot rule out a return of the steering symmetry for some class of non-Gaussian measurements, we note here that the system obeys Gaussian statistics in the operating regime investigated and Gaussian inference is at least as accurate as any other method for calculating the necessary correlations. Perhaps most importantly, this system is simpler than any other methods we are aware of which have been used or proposed to create asymmetric steering.

Diversity in pitch perception revealed by task dependence

Abstract: Pitch conveys critical information in speech, music, and other natural sounds, and is conventionally defined as the perceptual correlate of a sound's fundamental frequency (F0). Although pitch is widely assumed to be subserved by a single F0 estimation process, real-world pitch tasks vary enormously, raising the possibility of underlying mechanistic diversity. To probe pitch mechanisms we conducted a battery of pitch-related music and speech tasks using conventional harmonic sounds and inharmonic sounds whose frequencies lack a common F0. Some pitch-related abilities - those relying on musical interval or voice recognition - were strongly impaired by inharmonicity, suggesting a reliance on F0. However, other tasks, including those dependent on pitch contours in speech and music, were unaffected by inharmonicity, suggesting a mechanism that tracks the frequency spectrum rather than the F0. The results suggest that pitch perception is mediated by several different mechanisms, only some of which conform to traditional notions of pitch.

High-order harmonic mode-locked Yb-doped fiber laser based on a SnSe2 saturable absorber

Abstract: In this paper, tin diselenide (SnSe2) was successfully prepared with liquid phase exfoliation method and embedded into polyvinyl alcohol (PVA) as a saturable absorber (SA) for obtaining harmonic mode-locked Yb-doped fiber laser generations. Based on the fundamental frequency of 333 kHz, four kinds of high-order harmonic mode-locking (HML) with frequencies of 400, 460, 520 and 550 MHz were achieved, corresponding to 1200th, 1380th, 1560th and 1650th order harmonics, with maximum signal to noise ratios (SNRs: 40.55, 37.72, 36.42 and 34.18 dB) and maximum 3 dB spectrum widths (0.2043, 0.3448, 0.216 and 0.3033 nm) as well as minimum pulse widths (759.9, 567.7, 717.3 and 561.4 ps), respectively. This was the first demonstration focusing on the application of SnSe2 in high-order harmonic mode-locked Yb-doped fiber lasers and our results fully proved that SnSe2 had excellent performance in designing high frequency ultra-fast fiber lasers.