Performance studies of high-average-power picosecond optical parametric generation and amplification in MgO:PPLN at 80†MHz.

We report on performance studies of high-average-power single-pass picosecond optical parametric generation (OPG) and amplification (OPA) tunable near 2 µm in MgO:PPLN pumped by an Yb-fiber laser at 1.064 µm and 80 MHz pulse repetition rate. The simple setup based on two identical crystals, and without the need for an intermediate delay line for synchronization, delivers up to 6.3 W of average power at an overall conversion efficiency of ∼50% and is tunable across 1902-2415 nm. We present systematic characterization of OPG and OPA stages to compare their performance and investigate the effect of parametric generation in the high-gain limit, enabling high output power and full-width-half-maximum (FWHM) spectral bandwidths as large as 189 nm. The OPG-OPA output exhibits excellent passive power stability better than 0.3% rms and central wavelength stability better than 0.03% rms over 1 hour, in high spatial beam quality with M2<2. The OPG output pulses have duration of 5.2 ps with a FWHM spectral bandwidth of 117 nm at 2123 nm, resulting in a time-bandwidth product of ΔτΔν∼40, indicating ∼4 times temporal compression compared to the input pump pulses. Theoretical simulations confirm the effect of pump beam divergence on the observed shift in wavelength tuning with respect to temperature, while the exponential gain in the parametric process is identified as playing a key role in the resulting pulse compression.

Phase-locked picosecond optical parametric oscillator.

We report a degenerate self-phase-locked picosecond optical parametric oscillator (OPO) synchronously pumped by a mode-locked Yb-fiber laser at 1064 nm, delivering broadband output near 2 µm with 2.8 W of average power at ∼80MHz repetition rate. By exploiting a 50-mm-long MgO:PPLN crystal providing high gain and low group velocity dispersion under type-0 (e→ee) phase matching, the OPO generates a phase-locked degenerate output spectrum with a bandwidth of ∼202nm centered at 2128 nm in pulses of ∼21ps duration with excellent passive long-term power and spectral stability in high spatial beam quality. Phase-locked operation results in spectral and power stabilization at exact degeneracy and is further validated by f-2f interferometry and radio frequency measurements of OPO output. To the best of our knowledge, this is the first degenerate self-phase-locked OPO in picosecond time scale, and the highest average power reported for a phase-locked ultrafast OPO to date.

Experimental evolution of female traits under different levels of intersexual conflict in Drosophila melanogaster.

A number of studies have documented the evolution of female resistance to mate-harm in response to the alteration of intersexual conflict in the populations. However, the life-history consequence of such evolution is still a subject of debate. In this study, we subjected replicate populations of Drosophila melanogaster to different levels of sexual conflict (generated by altering the operational sex ratio) for over 45 generations. Our results suggest that females from populations experiencing higher level of intersexual conflict evolved increased resistance to mate-harm, in terms of both longevity and progeny production. Females from the populations with low conflict were significantly heavier at eclosion and were more susceptible to mate-harm in terms of progeny production under continuous exposure to the males. However, these females produced more progeny upon single mating and had significantly higher longevity in absence of any male exposure-a potential evidence of trade-offs between resistance-related traits and other life-history traits, such as fecundity and longevity. We also report tentative evidence, suggesting an increased male cost of interacting with more resistant females.

Reproductive behavior and fitness components in male Drosophila melaogaster are non-linearly affected by the number of male co-inhabitants early in adult life.

Although multiple lines of evidence suggest that early adult life is very important in shaping the reproductive behavior of males, few studies have looked at the fitness consequences of the variation in reproductive behavior induced by differences in early life experience of males. Using a long term laboratory adapted population of Drosophila melanogaster Meigen (Diptera: Drosophilidae), early life experience, in terms of co-inhabitant numbers, was found to affect male mating behavior and at least one fitness component. However, in contrast to previous studies, a non-linear relationship was found between early life experience and fitness components and a significant effect of co-inhabitant number on copulation duration and sperm defense. Both these traits showed a sharp increase as the co-inhabitant numbers changed from 1 to 16. However, there was a decline in the trait values as the co-inhabitant number increased further. The probable causes for the observed non-linear pattern of responses are discussed.