High-order derivative spectroscopy of rovibronic transitions using tunable diode-lasers

The technique of Frequency Modulation (FM) Spectroscopy has been used very successfully recently to perform several different types of measurements, with the applications of this technique growing as advances in semiconductor technology result in the availability of reliable, tunable single-mode semiconductor diode lasers in parts of the electromagnetic spectrum which were previously inaccessible. In this paper, a general theory of Nth order derivative spectroscopy is presented. Closed forms for the Nth (where N is any integer) derivatives of Gaussian, Lorentzian and Voigt lineshape functions are presented. Experimental measurements of absorption lines in the (electric dipole-forbidden and spin-forbidden) oxygen A band (the rotational lines in the 0<--0 vibrational rung of the b¹Σ⁺ _g<--X³Σ^-_g electronic transition) by using wavelength modulated absorption spectroscopy are given as an example. High-order (up to tenth) derivative measurements are presented, and compared with the theory developed