1. A method for calibrating an optical spectrograph having physical properties and a detector having a predetermined number of horizontal plane pixels, comprising the steps of: detecting a spectrum of a known source; referencing a table of known emission line wavelengths and known relative intensities, or known Raman vibration frequencies and relative intensities, or known intensity spectrum from a NIST calibrated intensity standard; deriving a spectrograph model in terms of model parameters based on the physical properties of the modeling spectrograph to approximate the observed spectrum; forming an intensity function based on said model spectrograph parameters and refining said spectrograph model parameters with a residual function to minimize residual difference between observed spectral intensities and spectral intensities calculated based on said intensity function.