Echelon parameters

I've been looking at the echelon parameters so we can predict which echelon order lines will end up in.  The best data I have are with the filter open and the gas cell (see below) so we know what wavenumbers fall in echelon orders that are divisible by simple integers.  The order in the center has two clear lines in it.  I know from previous observations with appropriate filters in place that the line closest to the center of the detector is 600.103 cm-1 seen in echelle order = 3 and the line in the same order near the bottom is 400.2217 cm-1 seen in echelle order = 2.  There is also a line near the top near column 400 that I know is 400.48451 cm-1. The central order is much stronger than all the other orders and also much cleaner at the ends of the slit (horizontal).  This makes it apparent that the echelon orders overlapping in the central order are multiples.  To the right and left of the central, clean order are various less intense, less contrasting orders.  Eventually, we see a clean order on both sides.  Again, this is an order where different echelon orders overlap exactly.  Mid-way between the clean orders are somewhat intense, somewhat clean orders.  These locations are echelon orders that are multiples of 2, but not of 3.  Since the echelon order separation is inversely proportional to the echelle order number, we can figure out the location of echelon orders divisible by 4 as well.

Starting with the TEXES echelon parameters for the echelon groove spacing (7589 microns), R number (tan of incidence angle: 9.8), and gamma angle (0.025 radians), I varied the parameters to have the 600.103 line near the center of an echelon order (near M1.00, the 400.2217 cm-1 in the lower half of an echelon order (>M2.00,<M2.40), and the 400.48451 cm-1 line in the upper half of an order (>M3.50,<M3.75).  Further more, M1 = 3/2. M2 and M3 = M2 + 1.

Results will be better when we do this at other wavelengths (13.7 microns? 1315 cm-1?), but currently have:

echelon groove spacing: d = 7589.0 microns
echelon R number (tan of incidence angle): R# = tan(theta) = 9.8
echelon gamma angle: gamma = 0.20


Working on IDL routine to simulate gas cell spectra using HITRAN files with these parameters (and echelle parameters).