ECH_DISP

Determine the dispersion in mm for a given wavelength

Description

Use the grating equation to calculate the echelle beta angle at the given wavelength in the given order. Then calculate it at the point where the dispersion is by definition zero. Knowing the focal length of the camera, calculate the dispersion in mm.

ECH_INIT must be called before calling this routine.

Invocation

CALLECH_DISP (WAVE, M, THETA, GAMMA, DEL, STATUS)

Arguments
READ WAVE REAL

Wavelength of point at which dispersion is to be calculated (Angstroms)

READ M INTEGER

Order number in which this wavelength lies (it doesn’t have to be within the free spectral range)

READ THETA REAL

Echelle theta angle corresponding to the current configuration (radians)

READ GAMMA REAL

Echelle gamma angle corresponding to the current configuration (radians)

WRITE DEL REAL

Dispersion (mm)

READ, WRITE STATUS INTEGER

Global status value

Bugs

None known.

Authors

C.J. Hirst UCL (ZUVAD::CJH)