Gratings


No. grooves blaze angle blaze recommended application efficiency curv
1. order range order channel dispersion
[lines/mm] [degrees] [Å] [Å] [Å/mm] [Å/pix]
T01 830 19 7700 6000-10000 1 red 52 0.78 Plot
3200-5000 2 blue 26 0.39
T03 600 17 9500 7500-11000 1 red 72 1.08  
3800-5500 2 blue 36 0.54
T04 600 13 7100 5500-9000 1 red 72 1.08 Plot
3200-4500 2 blue 36 0.54
T05 1200 17 4700 3700-6500 1 blue 36 0.54 Plot
T06 1200 26 7100 5500-9000 1 red 36 0.54 Plot
3200-4300 2 blue 18 0.27
T07 400 9 8000 5500-11000 1 red 108 1.62 Plot
3300-5000 2 blue 54 0.81
T08 600 9 4700 3500-6500 1 blue 72 1.08 Plot
T09 600 22 12000 8400-11000 1 red 72 1.08 Plot
5500-7500 2 red 36 0.54
3500-4500 3 blue 24 0.36
T10 830 30 11500 8400-11000 1 red 52 0.78 Plot
5500-7000 2 red 26 0.39
4500-5500 2 blue 26 0.39
T11 270 5 7200 5500-11000 1 red 160 2.40  
3200-4500 2 blue 80 1.20
T12 600 7 3800 3100-4800 1 blue 72 1.08 Plot
T13 300 4 4700 3500-5500 1 blue 144 2.16  
5500-7000 1 red 144 2.16


In order to test how precise is Twin in recovering the wavelength positions on the CCD, it's say how precise is rotating the gratings, we took a sequence of comparison lamp frames changing for and back the central wavelength. After measuring the position of several lines in every frame with the same central wavelength, we found that the blue arm recover the position of any line with a precision better than 0.1 pixel.
But the red arm show an error of several pixels when trying to come back to a previous position. We must study this effect deeply and try to improbe the grating rotation.
Some examples are shown :

Blue Arm


Red Arm


Santos Pedraz Marcos
Last modified: Jan 20 2001