Simulation of a Narrow Band Filter Response in a Fast
Narrow band interference filters (FWHM <=100 Angstroms)
working in a fast beam normally have a blue-shifted transmission curve
from that produced in a parallel or near-parallel beam. The amount of the
wavelength shift can be as much as ~20A for the f/3.1 KPNO 4-Meter Prime
Focus. Since the wavelength shift depends on the filter design, the thickness
of the materials used and their index, there is no simple way to predict
the blue-shifted profile. To simulate the response, George Jacoby
has written a simulation program to calculate an estimated profile.
Data needed for a simulation:
Telescope optical parameters: f-ratio to be simulated and the ratio
of the diameters of the primary and secondary mirrors. For the 4-meter
use f/3.1 and a mirror ratio of 0.4 .
Ten passband scans of the filter at tilts of 0, 2, 3, 4, 5, 6, 7, 8,
9, and 10 degrees. The scans can be made on the NOAO Perkin-Elmer
Lambda 9 Spectrophotometer using a special carrier for tilting the filter.
The scans should be with a slit width of 0.2-0.5nm and a data sampling
of 1-5 Angstroms and all the scans need to cover the exact same wavelength
region. All raw data files from the Lambda 9 (.spa files) must be
reduced with the RFD program on the Filter Lab computer. Note that the
reduced data files are text files with no extension. Here is a sample
of the family of curves at different tilt angles. The left-most curve is
for a 10 degree tilt.
To run a sample simulation:
Supply a name for the results file and compare it to the expected
results in NR823sim.txt
Logon to gemini and cd to /ftp/pub/deveny/sample.
Note the ten tilt data files NR823*D and the input file list
Run the program by typing "filt" using the file list NR823.tlt
Here is a plot of the final simulated profile.
To run your data:
Logon to gemini and ftp your data files to /ftp/pub/deveny
Create a data file list and run "filt".