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ALFOSC grisms

  • Grism design specs
  • Long slit grisms
  • Echelle-mode 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 39004320 2.3 6906.2 35012.4 3200-7070
    4 300 48005800 3.3 7108.1 36016.2 3200-9600
    5 i 300 65007000 3.5 8308.4 41516.8 5000-10700
    6 600 39004020 1.5 9804.1 490 8.2 3200-5810 Check grism 14
    7 600 53005260 1.7 13004.1 650 8.2 3650-7110
    8 i 600 65007030 1.4 20003.5 1000 7.0 5680-8580
    10 c 150 38003870 5.9 21018 10536 3300-11000
    11 c 200 52005000 4.6 38013 19026 3880-10630 g
    12 c i 75 73006930 12 19036 9572 5100-11000
    14 600 42884630 1.6 12003.8 6007.6 3200-6380 Check grism 6
    15 f 300 52685470 3.1 6508.4 32516.8 3200-9450 ? Check grism 4
    16 1000 40694280 0.86 2000 1.9 1000 3.8 3460-5220 Check grism 18
    17 2400 VPH
    6580 0.26100000.65 5000 1.3 6330-6870 ?
    18 1086 VPH
    4360 0.93 20002.2 1000 4.4 3450-5350 Check grism 16
    19 i 823 VPH
    5640 1.2 19402.9 970 5.8 4400-6950
    20 i 484 VPH
    7850 2.2 15405.1 770 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 OG515below 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 OG515start >7500Å TBD
    10c3300-11000 U 2.5% noticeable >6200; B 0.5% start >7500Å TBD
    11c3880-10630 14% at 4000Å noticeable >6900; B 4% start >7500Å TBD
    12c5100-11000 V 20% noticeable >9900; R 9% OG515start >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 OG420no fringes in wav range
    20 5650-10150no 2nd-order light in wav range OG550below 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

    a) Effective blaze wavelength, where measurements are available.
    c) Grisms 10, 11 and 12 are cross-dispersers for echelle grism 9. They can also be used as individual low-res grisms.
    f) Do not use grism 15: choose grism 4 instead.
    g) For Grism #11 in the filter wheel.
    i) Have an inbuilt order-blocker filter.
    j) This column lists the UBVR peak flux of the 2nd order wrt that of the 1st. These were measured with U#7, B#74, V#75, and R#76.
    k) The peak-to-peak fringe levels were measured with Slit_0.5 and the internal halogen lamp.


    Echelle mode

    Note that the below dispersions and wave ranges were measured with CCD8.
    With the current CCD14 the dispersion per pixel and the wave ranges are about 10% larger than indicated.

    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 orders0.4 @ 5000Å
    0.7 @ 7500Å
    4500
    3900
    1.1
    1.9
    2250
    1950
    2.2
    3.8
    3300-11000
    13 316 51005250 0.5 37001.4 18502.8 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

  • Grism design specs for grisms 3 - 15
  • Grism design specs for grism 16, and commisioning report
  • Grism design specs for VPH grism 17, and commisioning report
  • Grism design specs for VPH grisms 18 - 20, and commisioning report

  • Back to top Last modified: 19-May-2016