Ultrashort intense-field optical vortices produced with laser-etched mirrors

We introduce a simple and practical method to create ultrashort intense optical vortices for applications involving high-intensity lasers. Our method utilizes femtosecond laser pulses to laser-etch grating lines into laser-quality gold mirrors. These grating lines holographically encode an optical vortex. We derive mathematical equations for each individual grating line to be etched, for any desired (integer) topological charge. We investigate the smoothness of the etched grooves. We show that they are smooth enough to produce optical vortices with an intensity that is only a few percent lower than in the ideal case. We demonstrate that the etched gratings can be used in a folded version of our 2f-2f setup [Mariyenko et al., Opt. Express 19, 7599 (2005)] to compensate angular dispersion. Lastly, we show that the etched gratings withstand intensities of up to 10^12 W/cm2.Comment: 14 pages, 12 figures, submitted to Optics Expres

Imaging of Alignment, Deformation and Dissociation of CS2 Molecules using Ultrafast Electron Diffraction

Imaging the structure of molecules in transient excited states remains a challenge due to the extreme requirements for spatial and temporal resolution. Ultrafast electron diffraction from aligned molecules (UEDAM) provides atomic resolution and allows for the retrieval of structural information without the need to rely on theoretical models. Here we use UEDAM and femtosecond laser mass spectrometry (FLMS) to investigate the dynamics in carbon disulfide (CS2) following the interaction with an intense femtosecond laser pulse. We have retrieved images of ground state and excited molecules with 0.03 {\AA} precision. We have observed that the degree of alignment reaches an upper limit at laser intensities below the ionization threshold, and found evidence of structural deformation, dissociation, and ionization at higher laser intensities

Predator functional responses and the biocontrol of aphids and mites

Biocontrol with predators is a key tool for controlling agricultural pests and preserving the productive efficiency of crops. Determining which predators to use for biocontrol often involves measuring their functional response—the relationship between foraging rate and prey abundance, yet comparisons of functional responses across predators are complicated by differences in experimental procedures. Here we use a compilation of functional responses standardized for time and space units to illustrate key sources of variation in functional responses for predators being tested for control of aphids and mites. Our results show that arena size (as a proxy for habitat structure) is a crucial predictor of predator performance, indicating that assessments of functional responses on the crops of interest may be necessary for accurate comparisons. Our results also suggest that larger predators may generally be more efficient, and that warming linked to climate change could make biocontrol using predators more effective when pests are abundant

\u3ci\u3eIn Situ\u3c/i\u3e Measurement of Three-Dimensional Ion Densities in Focused Femtosecond Pulses

We image spatial distributions of Xeq+ ions in the focus of a laser beam of ultrashort, intense pulses in all three dimensions, with a resolution of ~3μm and ~12 μm in the two transverse directions. This allows for studying ionization processes without spatially averaging ion yields. Our in situ ion imaging is also useful to analyze focal intensity profiles and to investigate the transverse modal purity of tightly focused beams of complex light. As an example, the intensity profile of a Hermite-Gaussian beam mode HG1,0 recorded with ions is found to be in good agreement with optical images

Functional responses are maximized at intermediate temperatures

Functional responses describe how consumer foraging rates change with resource density. Despite extensive research looking at the factors underlying foraging interactions, there remains ongoing controversy about how temperature and body size control the functional response parameters space clearance (or attack) rate and handling time. Here, we investigate the effects of temperature, consumer mass, and resource mass using the largest compilation of functional responses yet assembled. This compilation contains 2,083 functional response curves covering a wide range of foragers and prey types, environmental conditions, and habitats. After accounting for experimental arena size, dimensionality of the foraging interaction, and consumer taxon, we find that both space clearance rate and handling time are optimized at intermediate temperatures (a unimodal rather than monotonic response), suggesting that the response to global climate change depends on the location of the consumer’s current temperature relative to the optimum. We further confirm that functional responses are higher and steeper for large consumers and small resources, and models using consumer and resource masses separately outperformed models using consumer:resource mass ratios, suggesting that consumer and resource body mass act independently to set interaction strengths. Lastly, we show that the extent to which foraging is affected by temperature or mass depends on the taxonomic identity of the consumer and the dimensionality of the consumer–resource interaction. We thus argue that although overall body size and temperature effects can be identified, they are not universal, and therefore food web and community modeling approaches could be improved by considering taxonomic identity along with body size and unimodal temperature effects

Foraging rates from metabarcoding: Predators have reduced functional responses in wild, diverse prey communities

Functional responses describe foraging rates across prey densities and underlie many fundamental ecological processes. Most functional response knowledge comes from simplified lab experiments, but we do not know whether these experiments accurately represent foraging in nature. In addition, the difficulty of conducting multispecies functional response experiments means that it is unclear whether interaction strengths are weakened in the presence of multiple prey types. We developed a novel method to estimate wild predators\u27 foraging rates from metabarcoding data and use this method to present functional responses for wild wolf spiders foraging on 27 prey families. These field functional responses were considerably reduced compared to lab functional responses. We further find that foraging is sometimes increased in the presence of other prey types, contrary to expectations. Our novel method for estimating field foraging rates will allow researchers to determine functional responses for wild predators and address long-standing questions about foraging in nature

Body Condition Helps to Explain Metabolic Rate Variation in Wolf Spiders

1. Metabolism is the fundamental process that powers life. Understanding what drives metabolism is therefore critical to our understanding of the ecology and behavior of organisms in nature. 2. Metabolic rate generally scales with body size according to a power law. However, considerable unexplained variation in metabolic rate remains after accounting for body mass with scaling functions. 3. We measured resting metabolic rates (oxygen consumption) of 227 field-caught wolf spiders. Then, we tested for effects of body mass, species, and body condition on metabolic rate. 4. Metabolic rate scales with body mass to the 0.85 power in these wolf spiders, and there are metabolic rate differences between species. After accounting for these factors, residual variation in metabolic rate is related to spider body condition (abdomen:cephalothorax ratio). Spiders with better body condition consume more oxygen. 5. These results indicate that recent foraging history is an important determinant of metabolic rate, suggesting that although body mass and taxonomic identity are important, other factors can provide helpful insights into metabolic rate variation in eco-logical communities

Temperature has a unimodal effect on the functional response of wolf spiders

The response of biotic interactions to changes in temperature will play a large role in determining the impact of climate change on ecological communities. In particular, how warming alters predator-prey interactions will influence population stability, food web connectivity, and the movement of energy across trophic levels. The functional response relates predator foraging rates to prey availability, and it is often predicted to increase monotonically with temperature, at least within the limits of predator function. However, some studies suggest that functional responses peak and then decline, and such a difference has critical implications for the effect of warming on ecological communities. Here we investigate the effect of temperature on the functional response of wolf spiders (Schizocosa saltatrix) foraging on midges. Our results clearly support a unimodal response of the functional response, with peak foraging occurring at normal daytime temperatures for the area. Thus, daytime active spiders might experience a decline in foraging with warming, while night active spiders might experience an increase in foraging. Together with previous work, our study strongly suggests that the widespread assumption of a monotonic increase in foraging with warming is not warranted

Creation of optical vortices in femtosecond pulses

We experimentally created a femtosecond optical vortex using a pair of computer-synthesized holographic gratings arranged in a 2f - 2f optical setup. We present measurements showing that the resulting donut mode is free of spatial chirp, and support this finding with an analysis of the optical wave propagation through our system based on the Kirchhoff- Fresnel diffraction integral. An interferogram confirms that our ultrashort vortex has topological charge 1, and a conservative experimental estimation of its duration is 280 fs. We used 25-fs radiation pulses (bandwidth approximately 40 nm) produced by a Ti:sapphire laser oscillator