High Power Few-Cycle Erbium Fiber Frequency Combs

Coherent optical sources from the ultraviolet (UV) to the mid-infrared (MIR) have been shown to be critical for a plethora of applications from quantitative chemical monitoring, molecular structure/function determination, to hyperspectral imaging. Optical frequency combs provide unique tools for spectroscopy due to their use in a dual comb modality, providing simultaneously large optical bandwidths with high resolution and fast data acquisition. While frequency combs readily exist in the near infrared, the UV, visible, and MIR remain a challenge for obtaining broadband comb coverage. In this dissertation I develop a simple and robust broadband frequency comb with coverage from the UV to the MIR by nonlinear frequency conversion from the near infrared, using a high power few-cycle erbium fiber frequency comb based on mature, robust, and low noise telecommunications technology. Utilizing conventional chirped pulse amplification and subsequent nonlinear broadening in fiber yields a scalable few-cycle system, supporting watts of optical power, with MW peak powers, while still maintaining few-cycle pulses. Single pass &chi;(2) nonlinear interactions in a bulk crystal yields coverage from 350 to 22400 nm, with coherence being demonstrated at either end of the spectrum. This table top coherent infrared source provides higher power spectral densities than a synchrotron, opening new avenues for long-wave infrared spectroscopy and imaging. In the visible, the combination of instantaneous bandwidths exceeding 100 THz with inherent comb mode resolution offers new regimes of ro-vibronic spectroscopy. Finally, with focused intensities of this source exceeding TW/cm2, non-perturbative high harmonic generation can be explored in solid-state semiconductors. Utilizing the comb properties of the high power few-cycle source allows for ultra-sensitive measurements of the carrier envelope phase dependent UV spectra (from 200 - 650 nm) and opens new avenues for exploring sub-cycle dynamics in high field physics.</p

Photochemistry of Nitrate Chemisorbed on Various Metal Oxide Surfaces

Atmospheric aerosols are known to provide an important surface for gas–solid interfaces that can lead to heterogeneous reactions impacting tropospheric chemistry. In this work, α-Fe2O3, TiO2, γ-Al2O3, SiO2 and ZnO, common components of atmospheric aerosols, served as models to investigate the gas–solid interface of nitric acid with aerosols in the presence of simulated solar radiation. Adsorbed nitrate and gaseous products can be continuously monitored with infrared spectroscopy (IR). Kinetic studies of adsorbed species were carried out using attenuated total reflectance infrared spectroscopy (ATR-FTIR). Ex situ simultaneous infrared spectroscopy of gas-phase products using a 2 m long path cell allowed the detection of gaseous products at early stages of the heterogeneous photochemical reaction. In addition, photoactive gaseous products, such as HONO, were detected as gas analysis was carried out outside the region of irradiation. All reactions were found to be first order with respect to adsorbed nitric acid and yielded gas-phase products such as NO, NO2, N2O4, N2O, and HONO. While the correlation between semiconductor properties of the metal oxide and the heterogeneous photochemical rate constant (j) is not direct, the semiconductor properties were found to play a role in the formation of relatively high proportions of greenhouse gas nitrous oxide (N2O)

Single-cycle all-fiber frequency comb

Single-cycle pulses with deterministic carrier-envelope phase enable the study and control of light-matter interactions at the sub-cycle timescale, as well as the efficient generation of low-noise multi-octave frequency combs. However, current single-cycle light sources are difficult to implement and operate, hindering their application and accessibility in a wider range of research. In this paper, we present a single-cycle 100 MHz frequency comb in a compact, turn-key, and reliable all-silica-fiber format. This is achieved by amplifying 2 $\mu$m seed pulses in heavily-doped Tm:fiber, followed by cascaded self-compression to yield 6.8 fs pulses with 215 kW peak power and 374 mW average power. The corresponding spectrum covers more than two octaves, from below 700 nm up to 3500 nm. Driven by this single-cycle pump, supercontinuum with 180 mW of integrated power and a smooth spectral amplitude between 2100 and 2700 nm is generated directly in silica fibers. To broaden applications,few-cycle pulses extending from 6 $\mu$m to beyond 22 $\mu$m with long-term stable carrier-envelope phase are created using intra-pulse difference frequency, and electro-optic sampling yields comb-tooth-resolved spectra. Our work demonstrates the first all-fiber configuration that generates single-cycle pulses, and provides a practical source to study nonlinear optics on the same timescale.Comment: Revised versio

Hilfsmittel und Verfahren für zellbasiertes high content imaging

Cell-based high content imaging has become a versatile and powerful method for studying e. g. cellular viability, morphology or physiology. However, high content imaging and its various applications require complex as well as expensive hardware and consumables, limiting its utility and usability. To broaden the applicability of cell-based high content imaging, we have developed tools and assaying techniques being exemplary portrayed in this article

An Illustration of Inverse Probability Weighting to Estimate Policy-Relevant Causal Effects

Traditional epidemiologic approaches allow us to compare counterfactual outcomes under 2 exposure distributions, usually 100% exposed and 100% unexposed. However, to estimate the population health effect of a proposed intervention, one may wish to compare factual outcomes under the observed exposure distribution to counterfactual outcomes under the exposure distribution produced by an intervention. Here, we used inverse probability weights to compare the 5-year mortality risk under observed antiretroviral therapy treatment plans to the 5-year mortality risk that would had been observed under an intervention in which all patients initiated therapy immediately upon entry into care among patients positive for human immunodeficiency virus in the US Centers for AIDS Research Network of Integrated Clinical Systems multisite cohort study between 1998 and 2013. Therapy-naïve patients (n = 14,700) were followed from entry into care until death, loss to follow-up, or censoring at 5 years or on December 31, 2013. The 5-year cumulative incidence of mortality was 11.65% under observed treatment plans and 10.10% under the intervention, yielding a risk difference of −1.57% (95% confidence interval: −3.08, −0.06). Comparing outcomes under the intervention with outcomes under observed treatment plans provides meaningful information about the potential consequences of new US guidelines to treat all patients with human immunodeficiency virus regardless of CD4 cell count under actual clinical conditions

The effect of antiretroviral therapy on all-cause mortality, generalized to persons diagnosed with HIV in the USA, 2009–11

Background: Although antiretroviral therapy (ART) is known to be protective against HIV-related mortality, the expected magnitude of effect is unclear because existing estimates of the effect of ART may not directly generalize to recently HIV-diagnosed persons