Pulse duration

About: Pulse duration is a research topic. Over the lifetime, 19429 publications have been published within this topic receiving 286507 citations.

Controlling HD+ and H+2 dissociation with the carrier-envelope phase difference of an intense ultrashort laser pulse.

Abstract: Carrier-envelope phase difference effects in the dissociation of the HD+ molecular ion in the field of an intense, linearly polarized, ultrashort laser pulse are studied in the framework of the time-dependent Schrodinger equation. We consider a reduced-dimensionality model in which the nuclei are free to vibrate along the field polarization and the electrons move in two dimensions. The laser has a central wavelength of 790 nm and a pulse length of 10 fs with intensities in the range 6x10(14) to 9x10(14) W/cm(2). We find that the angular distribution of dissociation to p+D and H+d can be controlled by varying the phase difference, generating differences between the dissociation channels of more than a factor of 2. Moreover, the asymmetry is nearly as large for H+2 dissociation.

Towards generation of mJ-level ultrashort THz pulses by optical rectification.

Abstract: Optical rectification of ultrashort laser pulses in LiNbO3 by tilted-pulse-front excitation is a powerful way to generate near single-cycle terahertz (THz) pulses. Calculations were carried out to optimize the output THz peak electric field strength. The results predict peak electric field strengths on the MV/cm level in the 0.3-1.5 THz frequency range by using optimal pump pulse duration of about 500 fs, optimal crystal length, and cryogenic temperatures for reducing THz absorption in LiNbO3. The THz electric field strength can be increased further to tens of MV/cm by focusing. Using optimal conditions together with the contact grating technique THz pulses with 100 MV/cm focused electric field strength and energies on the tens-of-mJ scale are feasible.

Acoustic communication in the gray treefrog, Hyla versicolor : evolutionary and neurobiological implications

Abstract: 1. Acoustic communication in the gray treefrog,H. versicolor, was studied by analyzing the vocalizations of males and observing the phonotactic behavior of gravid females in response to pairs of synthetic stimuli, which usually simulated choices between calls of conspecific males at different temperatures or choices between calls of conspecific males and those of a sibling species,H. chrysoscelis. Calls ofH. chrysoscelis were also analyzed acoustically. 2. Pulse duty cycle (pulse duration divided by pulse period) averaged about 0.50 in the calls of both species over a wide range of temperature (Table 1). Pulse rise-time (as a percentage of pulse duration), which was also temperature-independent, was significantly longer inH. versicolor than inH. chrysoscelis (Table 1). The species difference in pulse shape was evident at a distance of 10 m from calling frogs (Fig. 1). 3. Females strongly preferred a linear approximation to the pulse shape (rise-time) typical of conspecific calls to an approximation of the pulse shape typical ofH. chrysoscelis (Figs. 1, 2A). Females did not show a preference between linear and exponential approximations of the conspecific pulse shape (Figs. 1, 2B). 4. When offered choices between synthetic calls that differed in pulse rate (pulses per s=p/s), females were usually very selective, choosing a stimulus with a pulse rate typical of a conspecific male at the test temperature over alternatives that differed by as little as 25% (Figs. 4–6). When both the call rate and pulse rate of synthetic calls were changed (Fig. 3), females showed temperature-dependent reversals in preference between 16 and 24°C (16 p/s vs 25 p/s) and between 16 and 20°C (15 p/s vs 20 p/s), but not between 20 and 24°C (20 p/s vs 25 p/s) (Table 2A–C). 5. When the call rates of alternative stimuli were the same, the pulse rate selectivity of females at 20°C was biased toward stimuli with low pulse rates (Table 2F). Females tested at 16°C rejected strongly alternatives with a high pulse rate, but females tested at 24°C did not reject strongly alternatives with a low pulse rate (Table 2E). Females tested at 24°C were also less selective than females tested at 20°C in rejecting alternatives with a high pulse rate, in the range ofH. chrysoscelis (Table 2D). Females tested at 24°C did, however, strongly reject an alternative with both a pulse rate and pulse shape typical ofH. chrysoscelis (Fig. 6). 6. Call duration and call rate were also relevant properties; changes in these variables modified preferences based on differences in pulse rate, provided that the pulse rates of both alternatives were within the range of variation produced by conspecific males over the normal range of breeding temperatures (Figs. 4–6). 7. Females showed a weak preference for synthetic calls with a bimodal spectral structure typical of conspecific males (1.1 kHz [−6 dB]+2.2 kHz) to a synthetic call with a single spectral component of 2.2 kHz. In tests of single-component stimuli of 1.9 or 2.2 kHz against alternatives of lower and higher frequencies, female preferences indicated a pattern of relative frequency sensitivity (Fig. 7) that was similar to that of an audiogram based on evoked potentials in the midbrain over the same range of frequency. 8. About 50% of the females tested responded phonotactically to a recorded call ofH. chrysoscelis when they had no other choice (Table 3). Thus, heterospecific signals were not only audible, but also behaviorally effective in the context of courtship. 9. Pattern of female preferences with respect to pulse shape and pulse rate suggest that the potential for mismating with males ofH. chrysoscelis has been an important selective force in the evolution of acoustic pattern discrimination inH. versicolor. 10. Results of this study are compared with those of other anurans and acoustic insects. Temperature-dependent shifts in temporal pattern preference, similar but less pronounced than those reported here for both fine temporal and gross temporal properties, were found in some species but not in others. 11. The pulse rate of the male's call increases linearly over a wide range of temperature (9–34°C; Gayou 1984), but female selectivity for pulse rate differs within the range of 16–24°C and is biased toward low pulse rates (Table 2). Thus, it is unlikely that both the temporal patterning of the male's call and temporal pattern recognition by the female are controlled rigidly and linearly by the same neural circuitry. 12. We discuss neurophysiological studies of temporal pattern selectivity in acoustic insects and anurans. There are several neural correlates of behavioral selectivity in gray treefrogs, but no published data concerning a neural correlate of the asymmetry in the strength of pulse rate preferences in gray treefrogs.

More Intense, Shorter Pulses

Abstract: A few years ago, a new type of large-scale laser infrastructure specifically conceived to produce the highest peak power and focused intensity was announced: the Extreme Light Infrastructure, ELI ( 1 ), designed to be the first exawatt-class (1018 W) laser. This gargantuan power will be obtained by cramming a kilojoule of energy into a pulse only 10 fs in duration. Analysis of the history of laser development reveals that the pulse duration and intensity of lasers (or derived coherent radiation bursts) are linearly related over more than 18 orders of magnitude (see the figure). This observation leads us to the conclusion that the shortest coherent pulse should come from such a large-sized laser. If zeptosecond and perhaps yoctosecond pulses can be produced using kilojoule-megajoule systems, it would open a route to time-resolved nuclear physics exploration and the possibility of peeking into the nucleus interior in the same way that chemical reactions or atoms can be probed today.