The dispersive elements include grisms available on the Blue side and gratings that are available on the Red side. The grisms on the blue side are always installed and available to the observers. The gratings on the red side are available to observers, but need to be specified on the instrument configuration form to ensure that the desired gratings are installed during an observing session.

Grisms: Blue Side

The table below lists the grisms available for use with LRIS on the Blue Side only The values presented were empirically measured. Chuck Steidel (Caltech) supplied the wavelength ranges and efficiency data. The FWHM of lines using a 1 arcsec slit width were obtained using the internal lamps, and ranges in FWHM are from blue to red in wavelength. The efficiencies on the blue side are the efficiency of the instrument with that grism.
Efficiency Wavelenth Range (Å) Flat Field FWHM resolution for 1" slit
MOS Longslit
300/5000 1.43 data
2240-8090 1600-7450 8.4-9.2
400/3400 1.09 data
1790-6250 1300-5770 6.5-7.1
600/4000 0.63 data
3330-5910 3040-5630 3.8-4.1
1200/3400 0.24 data
3040-4030 2940-3920 1.56

Note: The efficiency data was acquired by Chuck Steide (4 June 2002). The efficiency plots reflect the efficiency of LRISb with each grism. For the 300, 400, & 600 grisms, the mirror was used at the position of the dichoric. The UV response improves with the use of dichroics instead of the mirror. The 1200 grism efficiency is in combination with the 460 dichroic. All other optics were the same for all grism observations. Below is a comparison plot of the instrument throughputs for the four grisms as measured by Chuck Steide (4 June 2002)

Gratings: Red Side

The following gratings are available for use with LRIS red side. The grating information is up to date for the red side upgrade. Dispersion and wavelength coverage are calculated and are not measured values. The efficiency plots are not up to date and were determined using the old detector.

Efficiency1 Δλ (Å) Flat Field FWHM resolution for 1" slit
150/7500 3.0 12288 n/a
300/5000 1.59 6525 n/a 9.18
400/8500 1.16 4762 n/a 6.9
600/5000 0.80 3275 4.7
600/7500 0.80 3275 4.7
Gold coated
0.80 3275 4.7
Gold coated
0.58 2375 n/a
900/5500 0.53 2175
1200/7500 0.40 1638
Gold coated
0.40 1638 TBD
Mirror n/a n/a n/a

1. The grating efficiency was measured by acquiring slitless spectra of spectrophotometric standard stars. The grating, standard star, date of observation, and filter(s) used are indicated on the plots. The spectra were reduced as follows:

Additional plots for the red side

In addition to the efficiency plots in the table above, several comparative plots between gratings of similar resolution are presented to illustrate crossover points and relative efficiencies.

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Med-res gratings
relative efficiencies
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