Molecular Structure and Modeling of Water-Air and Ice-Air Interfaces Monitored by Sum-Frequency Generation.

From a glass of water to glaciers in Antarctica, water-air and ice-air interfaces are abundant on Earth. Molecular-level structure and dynamics at these interfaces are key for understanding many chemical/physical/atmospheric processes including the slipperiness of ice surfaces, the surface tension of water, and evaporation/sublimation of water. Sum-frequency generation (SFG) spectroscopy is a powerful tool to probe the molecular-level structure of these interfaces because SFG can specifically probe the topmost interfacial water molecules separately from the bulk and is sensitive to molecular conformation. Nevertheless, experimental SFG has several limitations. For example, SFG cannot provide information on the depth of the interface and how the orientation of the molecules varies with distance from the surface. By combining the SFG spectroscopy with simulation techniques, one can directly compare the experimental data with the simulated SFG spectra, allowing us to unveil the molecular-level structure of water-air and ice-air interfaces. Here, we present an overview of the different simulation protocols available for SFG spectra calculations. We systematically compare the SFG spectra computed with different approaches, revealing the advantages and disadvantages of the different methods. Furthermore, we account for the findings through combined SFG experiments and simulations and provide future challenges for SFG experiments and simulations at different aqueous interfaces

Submillimeter local oscillators for spaceborne heterodyne applications

Existing and prospective submillimeter local oscillator technologies are surveyed and compared with respect to criteria of suitability for application in spaceborne submillimeter heterodyne receivers as those proposed for the Large Deployable Reflector (LDR). Solid-state and plasma devices are considered in terms of fundamental limitations

Comparison of direct and heterodyne detection optical intersatellite communication links

The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity

Technology needs assessment of an atmospheric observation system for tropospheric research missions, part 1

The technology advancements needed to implement the atmospheric observation satellite systems for air quality research were identified. Tropospheric measurements are considered. The measurements and sensors are based on a model of knowledge objectives in atmospheric science. A set of potential missions and attendant spacecraft and sensors is postulated. The results show that the predominant technology needs will be in passive and active sensors for accurate and frequent global measurements of trace gas concentration profiles

Multimodal microscopy in mid-infrared via flexible pulse shaping

In this thesis, mid-infrared (MIR) pulses with arbitrary temporal and spectral shape are generated via a difference-frequency process for application in a non-linear Raman microscope. Solely by shaping the sub 10 fs driving pulses, the broadband spectra of the MIR pulses are switched to narrowband and tuneable ones. In MIR transmission spectroscopy, these narrowband MIR spectra allow for investigating molecular vibrations from 1250 to 3250 cm-1 with spectral resolutions below 20 cm-1. Furthermore, MIR transmission microspectroscopy is combined with coherent-anti-Stokes Raman scattering (CARS) to provide a direct comparison of spectra and images obtained in one spot of the sample. Sum-frequency (SF) microspectroscopy is an additional technique, which complements the toolbox of this non-linear Raman microscope with the potential to investigate non-centrosymmetric systems. The flexibility of the pulse shaper allows for implementing two different SF-methods. Whereas the heterodyne multiplex method acquires the whole SF spectrum by imprinting only three different phase functions, the homodyne MIR-scanning method generates a high SF intensity directly linked to one vibrational mode. In all applications, the phase of MIR pulses must be well-known. This phase is determined in the focal plane of the microscope over more than 1000 cm-1 via two methods based on the dispersion-scan

Deep space communication and navigation study. Volume 1 - Summary

Comparison of alternative means for high data rate communication from deep space probes, and deep space navigation by orbiting spacecraf

Parametric analysis of microwave and laser systems for communication and tracking. Volume 2 - System selection

System selection criteria of microwave and laser systems for communication and tracking - Vol.