Tree-ring stable isotopes show different ecophysiological strategies in native and invasive woody species of a semi-arid riparian ecosystem in the Great Plains of the United States

Persistent shifts in riparian vegetation associated with the invasion of introduced Elaeagnus angustifolia and native nonriparian Juniperus virginiana have been reported in the U.S. Great Plains, with significant impacts on ecosystem services. In Nebraska, these species have been expanding into the native Populus deltoides riparian forests along the Republican River. Using dendrochronological data and stable isotope ratios, we examined the annual growth and acclimation strategies of these three species to climatic and streamflow variability. We hypothesized that the ability of invasive species to grow under a wide range of environmental conditions favour vegetation shifts at the expense of native species. Streamflow was the strongest predictor for performance. When accompanied with above-average annual precipitation, streamflow resulted in peak tree-ring widths in P. deltoides. J. virginiana showed less sensitivity, and E. angustifolia showed no response. delta O-18 values did not differ among species, which indicates that all species compete for the same water source. delta C-13 ratios and WUEi were higher in J. virginiana than in P. deltoides and E. angustifolia and increased in all species over time. E. angustifolia and P. deltoides exhibit a strong stomatal control and response to relative humidity relative to J. virginiana, which showed anisohydric stomatal behaviour. Our results show that once established, J. virginiana and E. angustifolia thrive in the understory of P. deltoides using different adaptive and acclimation strategies. Based on current water flow management, which prevents high-flood pulses through the riparian zone, these species will continue to establish and spread throughout the Republican River watershed

Femtosecond fiber-feedback optical parametric oscillator

We demonstrate what is to our knowledge the first synchronously pumped high-gain optical parametric oscillator (OPO) with feedback through a single-mode fiber. This device generates 2.3 to 2.7W of signal power in 700 to 900-fs pulses tunable in a wavelength range from 1429 to 1473nm. The necessary high gain was obtained from a periodically poled LiTaO3 crystal pumped with as much as 8.2W of power at 1030nm from a passively mode-locked YbYAG laser with 600-fs pulse duration and a 35-MHz repetition rate. The fiber-feedback OPO setup is compact because most of the resonator feedback path consists of a standard telecom fiber. Because of the high parametric gain, the fiber-feedback OPO is highly insensitive to intracavity losses. For the same reason, the synchronization of the cavity with the pump laser is not critical, so active stabilization of the cavity length is not required

Novel ultrafast parametric systems: high repetition rate single-pass OPG and fibre-feedback OPO

We describe two novel parametric systems for wavelength-tunable ultrashort pulse generation in the spectral range around 1.5 µm. We demonstrate the first single-pass optical parametric generator (OPG) that is directly pumped by a mode-locked laser at the full laser repetition rate of 35 MHz, obtaining up to 500 mW of average signal power with a pulse duration of 300 fs. We also report on a novel type of synchronously pumped high-gain optical parametric oscillator (OPO) with feedback through a single-mode fibre. We compare two fibre-feedback OPO systems, generating multi-watt average signal powers in 10 ps and 800 fs pulses. Both the OPG and fibre-feedback OPO system require a high parametric gain, which is achieved in periodically poled nonlinear crystals of LiNbO3 and LiTaO3, pumped with recently developed passively mode-locked all-solid-state lasers with very high average output power

Femtosecond fiber-feedback OPO

We demonstrate the first synchronously pumped high-gain optical parametric oscillator with feedback through a single-mode fiber. We obtained 2.7W in 900fs pulses at 1.45µm. An active cavity length stabilization is not required