Visible Radiation from Illuminating-Flare Flames: Strong Emission Features*†

Microwave-assisted modulation of light emission intensity in alkali-pyrotechnic plumes

“…(7) is contained implicitly in the free parameter X alk and its relationship with X mol . At flame and pyrotechnic temperatures, the quenching rate K M− approaches the thermal limit (8) where σ A is a cross section specific to each alkali, and μ e f f is the effective reduced mass of the alkali species with N 2 [24] . The complementary excitation rate K M+ is then constrained by the requirement of detailed balance.…”

“…The emission region grows to 3 to 4 cm in height from the burning surface. The emission enhancement of the flame is expected, in part, from the high alkali metal content of the formulations, which results in emission from low-lying electronic states [8][9][10][11][12] . For all formulations tested, microwave field application increased both the visible flame volume and emission intensity.…”

“…Herein, we refer to this approach as weak microwave induced plasma (WMIP), which is similar to conventional MIP but generated by relatively plume complex index of refraction n 0 , n amb total number density, plume and ambient T 0 , T amb gas temperature, plume and ambient weak (sub-breakdown) electric fields. For alkali-pyrotechnics, early research confirmed that visible and near-infrared (VIS/NIR) emission is dominated by spontaneous emission from electronically excited alkali atoms [8][9][10][11][12] , making the WMIP approach relevant for these systems. While direct electron collisions are thought to be the primary pathway for producing excess alkali emitters, indirect production by collisions with other excited molecules, like electronically-excited metastable nitrogen, may play a role [13] .…”

“…Modeling of emission in alkali-magnesium pyrotechnics has been performed, but only under the strict conditions of Boltzmann (electronic), Saha (ionic), and Planck (optical) equilibrium [8][9][10][11] . Still, relaxing these assumptions has become commonplace in plasma modeling [26] , and provides a framework for inclusion in pyrotechnic emission models.…”

A Mathematical Model of Flare Plume Combustion and Radiation

“…Many experimental and theoretical studies of the combustion of flares have been made to determine the details of the combustion and light emis.sion processes so that a better understanding of their operation could point the way to devising flares of greater luminosity or color purity. [1][2][3][4][5][6][7] Hlodel.ing of related phenomena has also been done.8…”