Sub two-cycle soliton-effect pulse compression at 800 nm in Photonic Crystal Fibers

The possibility of soliton self-compression of ultrashort laser pulses down to the few-cycle regime in photonic crystal fibers is numerically investigated. We show that efficient sub-two-cycle temporal compression of nanojoule-level 800 nm pulses can be achieved by employing short (typically 5-mm-long) commercially available photonic crystal fibers and pulse durations of around 100 fs, regardless of initial linear chirp, and without the need of additional dispersion compensation techniques. We envisage applications in a new generation of compact and efficient sub-two cycle laser pulse sources.Comment: 16 pages, 6 figure

A new species of frog of the genus \u3ci\u3ePristimantis\u3c/i\u3e (Strabomantidae) from a cloud forest in southern Peru

Frogs of the genus Pristimantis are found throughout northern South America in various habitats ranging from lowland rainforest, cloud forest and up to 4000 m in the puna. Members of the family Strabomantidae breed terrestrially without a free swimming tadpole; instead froglets hatch from terrestrially deposited eggs. Of the 455 known species of Pristimantis 123 are known from Peru. Here we describe a new species from the Cordillera Central in the Andes of southern Peru. The new species is known from only one female specimen. It is readily distinguished from all other members of the genus by a combination of a dark brown dorsum with large white blotches, absence of tympanic membrane and annulus, bright orange-red color in the groin and concealed surfaces of hind legs, and a distinct iris with intersecting vertical and horizontal streaks forming a cross. The new species is most similar with Pristimantis cruciocularis from the Andes of central Peru, but differs in several morphological characteristics such as size: Specimens of P. cruciocularis have a snout-vent length of 11.4–21.8 mm (n = 14) compared to 23.5 mm (n = 1) in the new species

Photon Echo Spectroscopy in the Single Optical-Cycle Regime

A very high temporal resolution and a broad bandwidth are but two advantages provided by the use of extremely short sub-5-fs pulses in a nonlinear spectroscopic experiment. However, the applicability of the standard theoretical description becomes questionable for the pulses that consist merely of a couple of optical oscillations. Far instance, the conventionally employed slowly varying envelope approximation, implying that the change of the pulse amplitude on the duration of an optical cycle is negligible compared to the magnitude of the amplitude itself, can no longer be maintained. Furthermore, the phase-matching bandwidth that is limited due to dispersion in the nonlinear medium rapidly gains importance with the increase of the spectral width of the pulse. Another point of serious concern is the frequency-dependent variation in the sensitivity of signal photodetectors. In combination, these features result in what is known as a spectral-filter effect. Finally, artificial lengthening of the experimental transients is a direct consequence of the noncollinear geometry employed in spectroscopic experiments. We present a theoretical analysis which thoroughly reexamines the formalism of ultrafast photon echo spectroscopy. We obtain a general expression for the echo signal, which is valid even for single-cycle-pulse applications. The derived formalism is applied to photon-echo spectroscopy on the hydrated electron with 5-fs pulses