FUNCTION AIRTOVAC(W)
      IMPLICIT REAL*8 (A-H,O-Z)
C     W IS AIR WAVELENGTH IN NM
C     WAVEN IS AIR WAVENUMBER WHICH IS USUALLY GOOD ENOUGH 
c
c     Edlen, B. 1966. Metrologia 2, 71.
c     quoted by 
c     Peck, E.R. and Reeder, K. 1972.  JOSA 62, 958-962.
c
C     MUST ITERATE FOR EXACT SOLUTION
      WAVEN=1.D7/W
      WNEW=W*(1.0000834213D0+
     1 2406030.D0/(1.30D10-WAVEN**2.)+15997.D0/(3.89D9-WAVEN**2.))
C    1(1.000064328+2949810./(1.46E10-WAVEN**2)+25540./(4.1E9-WAVEN**2))         
      WAVEN=1.D7/WNEW
      WNEW=W*(1.0000834213D0+
     1 2406030.D0/(1.30D10-WAVEN**2.)+15997.D0/(3.89D9-WAVEN**2.))
      WAVEN=1.D7/WNEW
      AIRTOVAC=W*(1.0000834213D0+
     1 2406030.D0/(1.30D10-WAVEN**2.)+15997.D0/(3.89D9-WAVEN**2.))
      RETURN
      END
      FUNCTION VACTOAIR(W)
      IMPLICIT REAL*8 (A-H,O-Z)
C     W IS VACUUM WAVELENGTH IN NM
      WAVEN=1.D7/W
      VACTOAIR=W/(1.0000834213D0+
     1 2406030.D0/(1.30D10-WAVEN**2)+15997.D0/(3.89D9-WAVEN**2))
      RETURN
      END