obj = XSRS(caN2fr, vRamanResponseSpectrumDt)
  caN2fr is the n2 times fr in [m2/W]
  vRamanResponseSpectrumDt is the spectrum of Raman Response
  (Green's) function shifted (zero freq at index 1) and with
  reverse frequency ordering (deffinition like in CTimeDimension)
 
  dA1 / dz \sim A1 (R * |A2|^2)
 
  options ae same as in SPM