The Role of Allelopathy on the Vegetational Composition of Disturbed Sites on the Samuel H. Ordway Memorial Prairie

The presence of large numbers of cattle in prairie sites can lead to the trampling and destruction of native vegetation in some areas. These damaged, or disturbed sites are typically invaded by a variety of undesirable alien plant species. Many of the alien plant species possess allopathic mechanisms. These allopathic mechanisms enable the alien species to dominate the disturbed sites, and prevent the re-establishment of native plant species. Attempts are currently underway to preserve remaining tracts of native prairie in South Dakota. The Samuel H. Ordway, Jr. Memorial Prairie in McPherson county is one such tract, and is the research site of this study. The tall and mid-grass prairies of the eastern Dakotas were historically maintained by grazing pressure and periodic fires. The primary management tool used at Ordway Prairie is limited grazing with cattle to simulate native herbivore grazing pressures. Burning is not currently a significant management tool. This research was conducted to identify the presence and distribution of allelopathic alien species in disturbed sites resulting from overgrazing by cattle Ordway Prairie. Recommendations will be made regarding management techniques designed to reduce the dominance of disturbed sites by alien species

Compressive Raman imaging with spatial frequency modulated illumination

We report a line scanning imaging modality of compressive Raman technology with spatial frequency modulated illumination using a single pixel detector. We demonstrate the imaging and classification of three different chemical species at line scan rates of 40 Hz

Line-scan Compressive Raman imaging with spatio-spectral encoding

We report a line-scanning imaging modality of Compressive Raman technology with a single-pixel detector. The spatial information along the illumination line is encoded onto one axis of a digital micromirror device, while spectral coding masks are applied along the orthogonal direction. We demonstrate imaging and classification of three different chemical species

The coherent artifact in modern pulse measurements

We simulate multi-shot intensity-and-phase measurements of unstable ultrashort-pulse trains using frequency-resolved-optical-gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER). Both techniques fail to reveal the pulse structure. FROG yields the average pulse duration and suggests the instability by exhibiting disagreement between measured and retrieved traces. SPIDER under-estimates the average pulse duration but retrieves the correct average pulse spectral phase. An analytical calculation confirms this behavior.Comment: submission to Opt. Let

Super resolution computational saturated absorption microscopy

Imaging beyond the diffraction limit barrier has attracted wide attention due to the ability to resolve image features that were previously hidden. Of the various super-resolution microscopy techniques available, a particularly simple method called saturated excitation microscopy (SAX) requires only a simple modification of a laser scanning microscope where the illumination beam power is sinusoidally modulated and driven into saturation. SAX images are extracted from harmonics of the modulation frequency and exhibit improved spatial resolution. Unfortunately, this elegant strategy is hindered by the incursion of shot noise that prevents high resolution imaging in many realistic scenarios. Here, we demonstrate a new technique for super resolution imaging that we call computational saturated absorption (CSA) in which a joint deconvolution is applied to a set of images with diversity in spatial frequency support among the point spread functions used in the image formation with saturated laser scanning fluorescence microscope. CSA microscopy allows access to the high spatial frequency diversity in a set of saturated effective point spread functions, while avoiding image degradation from shot noise.Comment: 26 pages, 15 figure

Learning from learning algorithms: application to attosecond dynamics of high-harmonic generation

Includes bibliographical references (pages 043404-5).Using experiment and modeling, we show that the data set generated when a learning algorithm is used to optimize a quantum system can help to uncover the physics behind the process being optimized. In particular, by optimizing the process of high-harmonic generation using shaped light pulses, we generate a large data set and analyze its statistical behavior. This behavior is then compared with theoretical predictions, verifying our understanding of the attosecond dynamics of high-harmonic generation and uncovering an anomalous region of parameter space

High-efficiency, single-stage 7-kHz high-average-power ultrafast laser system

Includes bibliographical references (page 467).We demonstrate a simple and practical single-stage ultrafast laser amplifier system that operates at a repetition frequency from 1 to 10 kHz, with millijoule pulse energy and as much as 13 W of average power. The repetition rate can be adjusted continuously from 1 to 10 kHz by new all-solid-state pump laser technology. This is to our knowledge the highest average power ever obtained from a single-stage ultrafast laser amplifier system. This laser will significantly increase the average power and the repetition rate that is easily accessible for high-field experiments such as coherent x-ray generation or for laser-synchrotron studies