Breaking through the geocoronal barrier: spectroscopic validation of the hydrogen absorption cell for Lyman-alpha attenuation

The Johns Hopkins Rocket Group is developing hydrogen absorption cell technology to mitigate the Lyman-alpha emission challenge posed by the geocorona for astronomical photometry in the Lyman ultraviolet spectrum (1000- 1216 Å) from low-Earth orbit. We have assembled a prototype cell from 1.33 SS CFF tube, two (2mm) LiF windows and a tungsten filament. The cell is filled with H₂ to a pressure of 2 torr. The heated filament thermally dissociates the H₂ into its atomic form, which will absorb Lyman-alpha. In theory, the pressure is high enough to collisionaly de-excite the H, thus preventing resonant re-scattering. <br/> <br/> We have begun testing and have preliminary results using the Long-slit Imaging Dual Order Spectrograph. Spectral testing of the Lyman-alpha line profiles are vital for advancing hydrogen absorption cell technology in future Lyman ultraviolet missions. These tests can reveal whether or not molecular hydrogen fluorescence is occurring from either electron impact excitation or recombination in higher energy states. Our preliminary results have shown attenuation of the source Lyman-alpha signal by roughly 73% with an associated optical depth of 1.3 and hydrogen column density of 2.2 x 10¹³. Future tests will involve cooling down our lamp/hydrogen cell system as well as testing multiple filament configurations for the most efficient input power possible.