TTF Wavelength Calibration
Long-slit spectra taken with the TTF and a CuAr source
through four filters: (top L) R1/710 nm, (top R) I3/760 nm, (bottom L)
I5/815 nm, (bottom R) I6/910 nm. The long-slit spectrum is achieved with
a focal plane slit, stepping the TTF through 80 frequencies synchronized
with moving the charge on the detector (charge shuffling). The seven strips
correspond to CS 100 coarse settings of (+6, +5, +4, +3, +2, +1, 0) spanning
a physical gap range of 12 to 5 micron (left to right). There are three
dominant emission lines in all filters, except the 910 nm filter with two
lines. The latter is the easiest for seeing the major effect, that the
orders separate out easily at small gap where the wavelength free spectral
range increases. But note, in particular, that the intrinsic spectral resolution
is falling as well.
From fitting to the lines as a function of wavelength
against y (row number), we have established the gap and order of interference,
m. The line wavelengths are given at the end. In the figure below, we plot
the coarse setting against the gap spacing for all four filters. The non-linear
variations along a mean slope are real.
The complete data from this calibration are summarised below.
There are four tables, one for each of the TTF blocking filters.
Click here for a textfile
CuAr Calibration Lines:
Dick Hunstead has estimated better values for the line blends
from Morlen (1973) Physica Scripta, 8, 249 with flux weighting. The first
number is the relative flux; zero means very faint line. Click here
for a textfile version.