Grism Selection Guide

Update: Feb 19, 2010

It is necessary to select the most suitable according to the wavelength resolution and sensitivity required.

Resolution vs. Wavelength	Efficiency vs. Wavelength
Resolution vs. Wavelength	VPH grisms	other grisms (incomplete)

General Notes:

The grisms shown in the blue panels below are ready for open-use. Others are being tested or under fabrication.
Spectral resolution (R = l /dl ) is almost proportional to the slit width, w, if w is greater than 0.2". In the following table, w = 0.4" is adopted. Generally, wider slit degrades the spectral resolution, but raises the sensitivity when CCD binning is properly done along the wavelength direction.

Grism name	Links to figures of efficiency, etc.	Lines or Grooves (mm^-1)	Order	Dispersion (A/pix)	Center WL (A)	Spectral Resolution with 0.4" slit	Order Cut Filter	Wavelength Coverage (A)	0th order?	2nd order?	Targets/Comments
Very low	Efficiency Design Drawing Holder	75	1	5.46	6500	250	SO58	5800-10000	YES	NO	Red MOS survey even @ >9400A
							SY47	4700-9000	YES	Overlap at >9000	Red MOS survey @ 4700-9400
							L600	3650-6000	YES	YES	Blue MOS survey
							L550	3400-5500	YES	YES	Blue MOS survey even @<3500A
Low	Efficiency Design Drawing [a] [b] [1] [2] [3] [4]	150	1	2.72	6500	500	SY47	4700-9000	NO	Overlap at >9000	Red Low disp.
							SO58	5800-10000	NO	NO	No 2nd order contami. even @ >9500A
							L600	3650-6000	NO	YES	Blue Low disp.
			2	1.4		700	L550	3400-5500	NO	YES	Highest sensitivity for <3800A
Middle Blue	Efficiency Throughput1 Throughput2 Design Drawing Holder	300	1	1.34	5500	1000	SY47	4700-8300	NO	YES	- Red Mid disp - Higher sens. than 300R @ <7800A - >8400A out of CCD
							SY47 offset slit	4700-9000	NO	Overlap at >9000	Larger spectral coverage
							L600	3650-6000	NO	YES	Blue Mid disp
							LC50	3300-6000	NO	YES(weak)	Sensitive even @ <3500A
							none	3650-8300	NO	Overlap at >7000	- Blue Mid disp - Higher efficiency - contamination by scattered light at <3800A
Middle Red	Efficiency Throughput1 Throughput2 Throughput3 Design Drawing	300	1	1.34	7500	1000	SY47	4900-9000	NO	YES	- Red Mid disp - Higher sens. than 300B @ >7800A - 4700-4900A out of CCD
			1	1.34	7500	1000	O58	5800-10000	NO	NO	No 2nd order contami. even @ >9500A
			2	0.67	3900	2000	L600	3650-5250	NO	---	Higher sens. than 300B 2nd
							L600 offset slit	3650-5950	NO	---	Higher sens. than 300B 2nd
							L550	3400-5250	NO	---	- Sensitive even @ <3500A - better blocking for 1st order contami.
Grism name	Links to figures of efficiency, etc.	Lines or Grooves (mm^-1)	Order	Dispersion (A/pix)	Center WL (A)	Spectral Resolution with 0.4" slit	Order Cut Filter	Wavelength Coverage (A)	0th order?	2nd order?	Targets/Comments
High Echelle	Efficiency Throughput Design Drawing Holder [1] [2]	175 (Echelle)	2	-0.98 @9300A	9720	2500	Cross Disp.	7900-10000	NO	---	opposite dispersion direction (Note 2)
							SDSS-z'	8300-10000	NO	---
							I offset slit	7300-8700	NO	---
			3	-0.63 @6600A	6550	2500	Cross Disp.	5400-7900	NO	YES
							I	7300-7900	NO	YES
							R	5900-7100	NO	YES
			4		4980		Cross Disp.	4200-5900	NO	YES
			5		4040		Cross Disp.	3600-4600	NO	YES
High 450	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1000 (VPH)	1	0.376	4500	4000	No filter	3800-5250	NO	NO	peak efficiency @ 4000A x shift = +16 pixel (Note 1)
High 450	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1000 (VPH)	1	0.376	4500	4000	No filter offset slit	4200-5650	NO	NO	peak efficiency @ 4000A x shift = +16 pixel (Note 1)
High 520	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1000 (VPH)	1	0.394	5250	4000	No filter	4450-6050	NO	NO	x shift = -47 pixel (Note 1)
High 520	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1000 (VPH)	1	0.394	5250	4000	No filter offset slit	4900-6500	NO	NO	x shift = -47 pixel (Note 1)
High 650	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	665 (VPH)	1	0.61 (average)	6500	2500	SY47	5300-7700	NO	NO	x shift = +222 pixel (Note 1)
			1	0.61 (average)	6500	2500	SY47 offset slit	5950-8350	NO	NO
			2	0.28 @4000A		3500	L600 offset slit	3650-4350	NO	---
			2	0.28 @4000A		3500	LC50	3300-4350	NO	---
High 850		360 (VPH)	1	1.18	8000	1700	SO58	5800-10350	NO	NO	x shift = -6 pixel (Note 1)
High 850		360 (VPH)	1	1.18	8000	1700	SO58 offset slit	6850-11650	NO	NO	x shift = -6 pixel (Note 1)
High 900		555 (VPH)	1	0.74	9000	3000	SO58	7500-10450	NO	NO	x shift = -120 pixel (Note 1)
High 900		555 (VPH)	1	0.74	9000	3000	SO58 offset slit	8300-11300	NO	NO	x shift = -120 pixel (Note 1)
Very High 680	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1600 (VPH)	1	0.223	6900	8000	SY47	6450-7350	NO	NO	x shift = +41 pixel (Note 1)
Very High 680	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1600 (VPH)	1	0.223	6900	8000	SY47 offset slit	6700-7600	NO	NO	x shift = +41 pixel (Note 1)
Very High 800	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1324 (VPH)	1	0.282	8000	7000	SY47	7500-8600	NO	NO	- not tested for polarimetry - x shift = -27 pixel (Note 1)
Very High 800	Throughput Prism Drawing Holder [1] [2] [3] [4] [5] [6]	1324 (VPH)	1	0.282	8000	7000	SY47 offset slit	7800-8900	NO	NO	- not tested for polarimetry - x shift = -27 pixel (Note 1)
Very High 950	Efficiency Throughput Drawing Prism drawing Holder [1] [2] [3] [4] [5] [6]	1095 (VPH)	1	0.352	9500	6000	O58	8860-10200	NO	NO	- Unavailable for polarimetry - x shift = -190 pixel (Note 1)
Grism name	Links to figures of efficiency, etc.	Lines or Grooves (mm^-1)	Order	Dispersion (A/pix)	Center WL (A)	Spectral Resolution with 0.4" slit	Order Cut Filter	Wavelength Coverage (A)	0th order?	2nd order?	Targets/Comments

Note

The VPH grisms produce image shifts along the slit direction (= orthogonal to the dispersion direction).
The values listed above are in pixels for 1x1 binning (~0".1/pixel) where positive values denote that the shift direction is from CCD chip1 to chip2.
The sign of this direction is opposite to that of "Shift_Sec" parameter in the "SetupField" command in OPE file.
The dispersion direction of the High Echelle grism is opposite to other grisms.
Therefore, the value of the dispersion is negative.