FLEET Velocimetry for Aerodynamics

Long-lasting emission from femtosecond excitation of nitrogen-based flows shows promise as a useful mechanism for a molecular tagging velocimetry instrument. The technique, known as femtosecond laser electronic excitation tagging (FLEET), was invented at Princeton a decade ago and has quickly been adopted and used in a variety of high-speed ground test flow facilities. The short temporal scales offered by femtosecond amplifiers permit nonresonant multiphoton excitation, dissociation, and weak ionization of a gaseous medium near the beam's focus without the generation of a laser spark observed with nanosecond systems. Gated, intensified imaging of the resulting emission enables the tracking of tagged molecules, thereby measuring one to three components of velocity. Effects of local heating and acoustic disturbances can be mitigated with the selection of a shorter-wavelength excitation source. This review surveys the development of FLEET over the decade since its inception, as it has been implemented in several test facilities to make accurate, precise, and seedless velocimetry measurements for studying complex high-speed flows.

Эмиссионные спектры молекулярных газов CHF-=SUB=-3-=/SUB=-, CCl-=SUB=-2-=/SUB=-F-=SUB=-2-=/SUB=-, SF-=SUB=-6-=/SUB=- в диапазоне 3-20 nm при импульсном лазерном возбуждении с использованием различных газовых струй в качестве мишеней

The article considers the results of studies of the emission spectra of CHF3, CCl2F2, SF6 upon excitation by pulsed laser radiation. We used Nd:YAG laser, λ = 1064 nm, τ = 5 ns, and Epulse = 0.8 J. The spectral range of 3-20 nm was studied. We used capillary and supersonic conical nozzles with dcrit = 145 μm, 2α = 12o, L = 5 mm, and dcrit = 450 μm, 2α = 11o, L = 5 mm to form an atomic cluster beam. The emission spectra for various gas targets were obtained, the obtained spectra were deciphered, and the ions emitting in this spectral range were determined. We observed that with increasing particle concentration in the zone of laser spark, the radiation intensity increases. In this case, the intensity of ion lines with high degrees of ionization increases faster.

The gaseous hydrocarbon fuel combustion process diagnostics using laser-spark emission spectrometry

To solve the gaseous hydrocarbon fuel combustion process control and diagnostics problem, it is proposed to apply the laser-spark emission spectrometry methods. In propane-air mixture combustion, three modes are investigated: stoichiometric combustion, an enriched mixture, and a lean mixture. A laboratory stand has been developed to study combustion processes by laser-spark emission spectrometry. The plasma radiation spectral characteristics an experimental study results formed in a flame when exposed to laser radiation are presented.

Эмиссионные спектры легких инертных газов Ne и Ar в диапазоне 3-20 nm при импульсном лазерном возбуждении с использованием различных газовых струй в качестве мишеней

The article considers the results of studies of the emission spectra of Ne and Ar upon excitation by pulsed laser radiation. We used Nd: YAG laser, λ = 1064 nm, τ = 5 ns, and Epulse = 0.8 J. The spectral range of 3-20 nm was studied. We used capillary and supersonic conical nozzles with dcr = 145 μm, 2α = 12o, L = 5 mm, and dcr = 450 μm, 2α = 11o, L = 5 mm to form an atomic cluster beam. The emission spectra for various gas targets were obtained, the obtained spectra were deciphered, and the ions emitting in this spectral range were determined. We observed that with increasing particle concentration in the zone of laser spark, the radiation intensity increases. In this case, the intensity of ion lines with high degrees of ionization increases faster.

Эмиссионные спектры молекулярных газов N-=SUB=-2-=/SUB=- и CO-=SUB=-2-=/SUB=- в диапазоне 3-20 nm при импульсном лазерном возбуждении с использованием различных газовых струй в качестве мишеней

The article considers the results of studies of the emission spectra of N2 and CO2 upon excitation by pulsed laser radiation. We used Nd: YAG laser, λ = 1064 nm, τ = 5 ns, and Epulse = 0.8 J. The spectral range of 3-20 nm was studied. We used capillary and supersonic conical nozzles with dcr = 145 μm, 2α = 12o, L = 5 mm, and dcr = 450 μm, 2α = 11o, L = 5 mm to form an atomic cluster beam. The emission spectra for various gas targets were obtained, the obtained spectra were deciphered, and the ions emitting in this spectral range were determined. We observed that with increasing particle concentration in the zone of laser spark, the radiation intensity increases. In this case, the intensity of ion lines with high degrees of ionization increases faster.

The sensitivity determination of energetic materials from laser spark spectrometry based on physical-parameter-corrected statistical methods

A simple method combining the impact of various factors on sensitivity is developed to determine various sensitivities via laser spark spectrometry with the consumption of only several milligrams of EM, rather than via macro-detonation testing.

Эмиссионные спектры тяжелых инертных газов Kr, Xe в диапазоне 3-20 nm при импульсном лазерном возбуждении с использованием различных газовых струй в качестве мишеней

The article considers the results of studies of the emission spectra of Kr, Xe upon excitation by pulsed laser radiation. We used Nd: YAG laser, λ = 1064 nm, τ = 5 ns, and Epulse = 0.8 J. The spectral range of 30-200A was studied. We used capillary with d = 500 μm and supersonic conical nozzles with dcr = 145 μm, 2α = 12o, L = 5 mm, and dcrit = 450 μm, 2α = 11o, L = 5 mm to form a gas jet. The emission spectra for various gas targets were obtained, the obtained spectra were deciphered, and the ions emitting in this spectral range were determined. We observed that with increasing particle concentration in the zone of laser spark, the radiation intensity increases. In this case, the intensity of ion lines with high degrees of ionization increases faster.