ALFOSC grisms

This page is valid for the new CCD14, and is still under construction.
The wave ranges and dispersions in the two tables below are updated, but the linked efficiency plots not yet.

Grism	rules/mm	blazea	central	dispersion	resolution for 0.5 arcsec slit		resolution for 1.0 arcsec slit			Note
		[Å]	[Å]	[Å/pixel]	R=/	[Å]	R=/	[Å]	[Å]
3	400	3900	4320	2.3	690	6.2	350	12.4	3200-7070
4	300	4800	5800	3.3	710	8.1	360	16.2	3200-9600
5 i	300	6500	7000	3.5	830	8.4	415	16.8	5000-10700
6	600	3900	4020	1.5	980	4.1	490	8.2	3200-5810	Check grism 14
7	600	5300	5260	1.7	1300	4.1	650	8.2	3650-7110
8 i	600	6500	7030	1.4	2000	3.5	1000	7.0	5680-8580
10 c	150	3800	3870	5.9	210	18	105	36	3300-11000
11 c	200	5200	5000	4.6	380	13	190	26	3880-10630 g
12 c i	75	7300	6930	12	190	36	95	72	5100-11000	Grating deteriorated
14	600	4288	4630	1.6	1200	3.8	600	7.6	3200-6380	Check grism 6
15 f	300	5268	5470	3.1	650	8.4	325	16.8	3200-9450 ?	Check grism 4
16	1000	4069	4280	0.86	2000	1.9	1000	3.8	3460-5220	Obsolete: use grism 18 instead !
17	2400 VPH		6580	0.26	10000	0.65	5000	1.3	6330-6870 ?
18	1086 VPH		4360	0.93	2000	2.2	1000	4.4	3450-5350	Check grism 16
19 i	823 VPH		5640	1.2	1940	2.9	970	5.8	4400-6950
20 i	484 VPH		7850	2.2	1540	5.1	770	10.3	5650-10150

Grism	[Å]	2nd order j	inbuilt order blocker	Peak-to-peak fringe levels k
3	3200-7070	U 20% noticeable >6100		no fringes in wav range
4	3200-9600	U 20% noticeable >5900; B 5%		below 1.5% <8000Å ; 4% at 9000Å
5	5000-10700	B/V 20% noticeable >9700	OG515	below 1.5% <8000Å ; 4% at 9000Å ; 10% at 10000Å
6	3200-5810	no 2nd-order light in wav range		no fringes in wav range
7	3650-7110	U >10% noticeable >6200		no fringes in wav range
8	5680-8580	no 2nd-order light in wav range	OG515	start >7500Å TBD
10c	3300-11000	U 2.5% noticeable >6200; B 0.5%		start >7500Å TBD
11c	3880-10630	14% at 4000Å noticeable >6900; B 4%		start >7500Å TBD
12c	5100-11000	V 20% noticeable >9900; R 9%	OG515	start >7500Å TBD
14	3200-6380	no 2nd-order light in wav range		no fringes in wav range
15f	3200-9450 ?	U 25% noticeable >6100; B 5%		start >7500Å TBD
16	3460-5220	no 2nd-order light in wav range		no fringes in wav range
17	6330-6870 ?	no 2nd-order light in wav range		no fringes in wav range ??
18	3450-5350	no 2nd-order light in wav range		no fringes in wav range
19	4400-6950	no 2nd-order light in wav range	OG420	no fringes in wav range
20	5650-10150	no 2nd-order light in wav range	OG550	below 2% <8000Å ; 4% at 9000Å ; 10% at 10000Å

Click on the waveband to obtain an efficiency/transmission curve.
Click here for count rates.

Notes to the tables

Echelle mode

Grism	rules/mm	blazea	central	dispersion	resolution for 0.5 arcsec slit		resolution for 1.0 arcsec slit
		[Å]	[Å]	[Å/pixel]	R=/	[Å]	R=/	[Å]	[Å]
9	79	17 orders		0.4 @ 5000Å 0.7 @ 7500Å	4500 3900	1.1 1.9	2250 1950	2.2 3.8	3300-11000
13	316	5100	5250	0.5	3700	1.4	1850	2.8	4800-5800 ? d
13	316	4 orders		0.35 @ 4050Å 0.5 @ 5250Å	4300 3700	1.0 1.4	2150 1850	2.0 2.8	3350-8660 ? h

Notes:
a) Effective blaze wavelength, where measurements are available.
d) This range is obtained with a special order sorter filter which is mounted in a square ALFOSC filterholder and located in its own drawer.
    The filter has NOT filter ID #124 (see the filter list).
h) This wavelength range has gaps and is obtained with grism #10 as cross-disperser (see below).

Grisms #9 and #13 are Echelle grisms, that image multiple orders on the CCD. They have to be used together with a cross-disperser (Gr #10, #11, #12) or with an order sorting filter. Below the possible setups are described. Note that special Echelle slitlets need to be used when a cross disperser is used.

• Grism 9+10: spacial order overlap bluer than 4250Å, for the standard 8 arcsec slit length. The total wavelength range sampled is 3300-10350Å; the wavelength range with proper inter-order spacing is 4250-10350Â.
  Cross-disp is flipped with respect to g9+11 and g9+12.

• Grism 9+11: noticable 2nd order effects (2nd order of g11) redward from 7400Å. The total wavelength range sampled is 3900-10350Å.

• Grism 9+12: Good throughput in the red, but not very useful. Cross-dispersion too low except for echelle orders 6,7,8 corresponding to 7500-11000Å. Redward from 10000Å there are very significant 2nd order effects (from g12). Note that the Loral chip fringes 40% peak-to-peak in echelle order 7 (around 9500Å).

• Grism 13+10: Grism 13 is usualy used with an order sorting filter in 3rd order, but can also be used with a cross-disperser. Grism 13+10 give an alternative for Grism 9+10, as spacial overlap is not a problem for this combination. For medium-resolution spectroscopy bluer than 4250Å this option is preferred over Grism 9+10. The orders of Grism 13 are too long for the chip: the total wavelength coverage is 3350-3610 (5th order), 3720-4430, 4770-5830, 7020-8660 (2nd order).

Grism design data, and commissioning reports