pro airtovac,wave_air, wave_vac ;+ ; NAME: ; AIRTOVAC ; PURPOSE: ; Convert air wavelengths to vacuum wavelengths ; EXPLANATION: ; Wavelengths are corrected for the index of refraction of air under ; standard conditions. Wavelength values below 2000 A will not be ; altered. Uses relation of Ciddor (1996). ; ; CALLING SEQUENCE: ; AIRTOVAC, WAVE_AIR, [ WAVE_VAC] ; ; INPUT/OUTPUT: ; WAVE_AIR - Wavelength in Angstroms, scalar or vector ; If this is the only parameter supplied, it will be updated on ; output to contain double precision vacuum wavelength(s). ; OPTIONAL OUTPUT: ; WAVE_VAC - Vacuum wavelength in Angstroms, same number of elements as ; WAVE_AIR, double precision ; ; EXAMPLE: ; If the air wavelength is W = 6056.125 (a Krypton line), then ; AIRTOVAC, W yields an vacuum wavelength of W = 6057.8019 ; ; METHOD: ; Formula from Ciddor 1996, Applied Optics 62, 958 ; ; NOTES: ; Take care within 1 A of 2000 A. Wavelengths below 2000 A *in air* are ; not altered. ; REVISION HISTORY ; Written W. Landsman November 1991 ; Use Ciddor (1996) formula for better accuracy in the infrared ; Added optional output vector, W Landsman Mar 2011 ; Iterate for better precision W.L./D. Schlegel Mar 2011 ;- On_error,2 compile_opt idl2 if N_params() EQ 0 then begin print,'Syntax - AIRTOVAC, WAVE_AIR, [WAVE_VAC]' print,'WAVE_AIR (Input) is the air wavelength in Angstroms' return endif wave_vac = double(wave_air) g = where(wave_vac GE 2000, Ng) ;Only modify above 2000 A if Ng GT 0 then begin for iter=0, 1 do begin sigma2 = (1d4/double(wave_vac[g]) )^2. ;Convert to wavenumber squared ; Compute conversion factor fact = 1.D + 5.792105D-2/(238.0185D0 - sigma2) + \$ 1.67917D-3/( 57.362D0 - sigma2) wave_vac[g] = wave_air[g]*fact ;Convert Wavelength endfor if N_params() EQ 1 then wave_air = wave_vac endif return end