Accurate wavelengths for highly-ionized L-shell spectra were measured in the 10–16Å region. The purpose being to determine lines in coincidence with L-shell transitions from the elements oxygen, fluorine, and neon. L-shell transitions have been proposed for resonant photopumping of K-shell electrons in these elements to, generate lasing between upper levels in the 40–150 eV region. The current effort improves on and expands the earlier spectroscopic work performed at KMS Fusion, Inc., where possible line coincidences were identified for photoionizing in the 1–3 and 1–4 levels in fluorine. New experimental techniques have led to a wavelength accuracy now believed to be ± 2 mÅ for cases in which adequate calibration lines are available. Exact spectral line matches were found for Mn with the F H,-line at 12.643Å and for both Mn and Cr with the F He line at 14.458Å. The Mn line at 12.643Å has been identified, using ab initio atomic structure calculations, as the 1D2 − 1F3 transition in Be-like Mn XXII. The Mn line emissivity was determined to be 30 MW into 2 steradians for a conversion efficiency of 0.04%. Photopumping with Mn coated gasfilled targets is presently being tried in gain measurement experiments at LLNL.