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Full-Text Articles in Mechanical Engineering
Interference-Free Gas-Phase Thermometry At Elevated Pressure Using Hybrid Femtosecond/Picosecond Rotational Coherent Anti- Stokes Raman Scattering, Joseph D. Miller, Chloe Elizabeth Dedic, Sukesh Roy, James R. Gord, Terrence R. Meyer
Interference-Free Gas-Phase Thermometry At Elevated Pressure Using Hybrid Femtosecond/Picosecond Rotational Coherent Anti- Stokes Raman Scattering, Joseph D. Miller, Chloe Elizabeth Dedic, Sukesh Roy, James R. Gord, Terrence R. Meyer
Terrence R Meyer
Rotational-level-dependent dephasing rates and nonresonant background can lead to significant uncertainties in coherent anti-Stokes Raman scattering (CARS) thermometry under high-pressure, lowtemperature conditions if the gas composition is unknown. Hybrid femtosecond/picosecond rotational CARS is employed to minimize or eliminate the influence of collisions and nonresonant background for accurate, frequency-domain thermometry at elevated pressure. The ability to ignore these interferences and achieve thermometric errors of <5% is demonstrated for N2 and O2 at pressures up to 15 atm. Beyond 15 atm, the effects of collisions cannot be ignored but can be minimized using a short probe delay (~6.5 ps) after Raman excitation, …
Single-Shot Gas-Phase Thermometry Using Purerotational Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering, Joseph D. Miller, Sukesh Roy, Mikhail N. Slipchenko, James R. Gord, Terrence R. Meyer
Single-Shot Gas-Phase Thermometry Using Purerotational Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering, Joseph D. Miller, Sukesh Roy, Mikhail N. Slipchenko, James R. Gord, Terrence R. Meyer
Terrence R Meyer
High-repetition-rate, single-laser-shot measurements are important for the investigation of unsteady flows where temperature and species concentrations can vary significantly. Here, we demonstrate singleshot, pure-rotational, hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps RCARS) thermometry based on a kHz-rate fs laser source. Interferences that can affect nanosecond (ns) and ps CARS, such as nonresonant background and collisional dephasing, are eliminated by selecting an appropriate time delay between the 100-fs pump/Stokes pulses and the pulse-shaped 8.4-ps probe. A time- and frequency-domain theoretical model is introduced to account for rotational-level dependent collisional dephasing and indicates that the optimal probe-pulse time delay is 13.5 ps …
Dual-Pump Vibrational/Rotational Femtosecond/ Picosecond Coherent Anti-Stokes Raman Scattering Temperature And Species Measurements, Chloe Elizabeth Dedic, Joseph D. Miller, Terrence R. Meyer
Dual-Pump Vibrational/Rotational Femtosecond/ Picosecond Coherent Anti-Stokes Raman Scattering Temperature And Species Measurements, Chloe Elizabeth Dedic, Joseph D. Miller, Terrence R. Meyer
Terrence R Meyer
A method for simultaneous ro-vibrational and pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) is presented for multi-species detection and improved temperature sensitivity from room temperature to flame conditions. N2∕CH4 vibrational and N2∕O2∕H2 rotational Raman coherences are excited simultaneously using fs pump pulses at 660 and 798 nm, respectively, and a common fs Stokes pulse at 798 nm. A fourth narrowband 798 nm ps pulse probes all coherence states at a time delay that minimizes nonresonant background and the effects of collisions. The transition strength is concentration dependent, while the distribution among observed transitions is related to temperature through …
Broadband Coherent Anti-Stokes Raman Scattering Spectroscopy Of Nitrogen Using A Picosecond Modeless Dye Laser, Sukesh Roy, Terrence R. Meyer, James R. Gord
Broadband Coherent Anti-Stokes Raman Scattering Spectroscopy Of Nitrogen Using A Picosecond Modeless Dye Laser, Sukesh Roy, Terrence R. Meyer, James R. Gord
Terrence R Meyer
Broadband picosecond coherent anti-Stokes Raman scattering (CARS) spectroscopy of nitrogen is demonstrated using 145-ps pump and probe beams and a 115-ps Stokes beam with a spectral bandwidth of 5 nm. This is, to our knowledge, the first demonstration of broadband CARS using subnanosecond lasers. The short temporal envelope of the laser pulses and the broadband spectral nature of the Stokes beam will enable nonresonant-background-free, single-shot, or time-dependent spectroscopy in high-pressure or hydrocarbon-rich environments. Successful correlation of room-temperature broadband picosecond N2 CARS with a theoretical spectrum is presented.