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Electro-Optical Systems Engineering

Grating Spectrograph Designer

Units and System Parameters

Hide Description Value Hide Description Value
Unit of Distance Unit of Angle At Object
Unit of Wavelength Central Wavelength [micron]
System Imaging Focal Length [m]

Object Parameters

Hide Description Value Hide Description Value
Slit Length at Object [rad] Diffraction Limit at Object [rad]

Telescope Parameters

Hide Description Value Hide Description Value
Telescope Pupil Diameter [m] Telescope Focal Length [m]
Telescope Focal Ratio Telescope Plate Scale [rad/m]
Slit Length at Telescope Focus [m] Diffraction Limit at Telescope [m]

Slit Parameters

Hide Description Value Hide Description Value
Slit Width at Object [rad] Slit Width at Telescope Focus [m]
Projected Slit Width [pixel]

Collimator Parameters

Hide Description Value Hide Description Value
Collimator Focal Length [m] Collimator Beam Size [m]

Grating Parameters

Hide Description Value Hide Description Value
Grating Groove Pitch [line/mm] Grating Order
Grating Input Angle (alpha) [deg] Grating Spectrograph Angle [deg]
Grating Beam Ratio Grating Length [m]
Grating Free Spectral Range [micron] Grating Free Spectral Range [pixel]
Grating Dispersion [micron/pixel] Grating Dispersion [m/s/pixel]
Grating Dispersion [R-pixel] Grating Dispersion [micron/slit]
Grating Dispersion [m/s/slit] Grating Dispersion [R-slit]

Camera Parameters

Hide Description Value Hide Description Value
Camera Focal Length [m] Camera Imaging Focal Ratio
Camera Half-Width [deg]

Detector Parameters

Hide Description Value Hide Description Value
Detector Pixel Size [micron] System Imaging Plate Scale [pixel/rad]
Detector Width [pixel]

Diffraction parameters

Hide Description Value Hide Description Value
Diffraction Limit (cross-disp) [pixel] Diffraction Limit (disp-dir) [pixel]

Secondary Wavelengths

Hide Description Value Hide Description Value
Lo Wavelength [micron] Hi Wavelength [micron]



	    
	    
	    
	

Instructions:

  • This web page is a multi-directional spreadsheet. All the cells are interlinked, so setting one cell might change any other cell.
  • The "enter" key or the button will fill in the derivable values.
  • Checking the "Hide" boxes will make the variable not show.
  • will show all variables, even internal variables of no interest.
  • will set the variables back to the values since the last .
  • For earlier values, use the browser's button.
  • The spreadsheet silently ignores non-numeric or invalid input.

If the values come up in red, then there is some problem, which is usually the fault of the user. The most likely causes are:

  • A set of variables was picked that is overdetermined. Using "enter" after every entry will prevent this.
  • The input values do not correspond to a physically realizable system.
  • Some unusual branch-cut was encountered, not already known to the program.
  • The program does not know how to take limits, so values close to lim{ (x→0)/(y→0) } will be incorrect.
  • Sometimes the grating angles are 180 degrees off. Not sure why this happens.

Also, some capabilities of the underlying program are not implemented by the web interface. Mainly, this is when "LOOP" appears, which means that a ring of variables exist which could in theory be solved, but the program needs to be given a starting value.

To-do list:

  • There are cases where a variable could be dropped out of the equations, but the program does not know to do so.
  • Change to column-down ordering, rather than side-by-side
  • Initial values for LOOP's
  • Add Javascript to check validity of input values
  • Grism and prism versions

The code for this tool has not been touched since 2007. Expect some amount of bitrot.