  Present day solar imaging spectrometers typically yield a few hundred million
spectra in one hour of observing time. This number will increase by an order of
magnitude for future instruments with larger 4k x 4k sensors as planned to be
used for the upcoming DKIST solar telescope. A fast quantitative analysis of
such huge data volumes can be done by comparing the observations to an archive
of pre-calculated synthetic spectra to infer the thermodynamic properties of
the atmosphere. To analyze intensity spectra of the Ca II IR line at 854 nm in
the solar atmosphere, we generated an archive with 2,000,000 spectra under the
assumption of non-local thermodynamic equilibrium (NLTE) with the NICOLE code
(Socas-Navarro et al, 2015). We tested its performance by inverting 60 spectral
scans of Ca II IR at 854 nm in the magnetically quiet Sun with 700,000 profiles
each. Based on the inversion results obtained using the full archive, we
construct a smaller archive by keeping only the about 70,000 archive profiles
that were actually used. We can reproduce the observed intensity spectra to
within a few percent using either the full or the small archive. For spectra
with 30 wavelength points, this NLTE inversion approach takes 0.02 (0.35) s per
profile to obtain a temperature stratification when using the small (full)
archive, i.e., it can invert a single spectral scan in about 4 (68) hrs. The
code is able to simultaneously deal with an arbitrary number of spectral lines.
This makes it a promising tool for deriving thermodynamic properties of the
solar atmosphere from current or future solar high-resolution observations of
photospheric and chromospheric lines.
