Over the past ten years more and more progress has been made toward the redefinition of the second using an optical atomic transition. Thereby replacing the microwave hyperfine transition of Cesium-133 as the SI standard. Researchers at the National Institute of Standards and Technology (NIST) have measured the new candidate optical standards relative to the current cesium reference, a necessary step to establishing a new standard. Taking 79 runs of data over the course of eight months they achieved a absolute frequency measurement with a fractional uncertainty of 2.1x10^-16
Combustion of fossil fuels is the primary supply of global energy demand and it is expected to remain nearly that way for the foreseeable future. However, incomplete combustion of hydrocarbon fuels can reduce the energy conversion efficiency while releasing a variety of harmful air pollutants. With advanced laser-based diagnostics techniques, spatially and temporally resolved physical and chemical parameters such as turbulent mixing, chemical species concentration, temperature, and pressure can be obtained in order to better understand and optimize the combustion process. Traditionally, nanosecond (ns)-duration lasers have been extensively used in various reacting and non-reacting flow diagnostics, however, such diagnostic approaches are often limited by slow data acquisition rates and laser-induced photochemical interferences. In recent years, ultrashort, femtosecond (fs)-duration laser pulses have been demonstrated for photolytic-interference-free species measurements and for high-speed data acquisition (e.g., 1-10 kHz) in various combustion/plasma systems. This talk will highlight the benefit of fs laser pulses, and discuss the utilization of them for two-photon laser-induced fluorescence (TPLIF) of atomic and molecular species detection in flames. Fs-TPLIF imaging measurements in those systems will be demonstrated, and the application of fs laser pulses at elevated pressure will be also discussed.