Disclosed herein are systems and methods of obtaining a derivative Raman spectrum using an excitation or Raman pump beam whose wavelength is modulated in any suitable manner such as, for example, stochastically. Shifting the wavelength of the input excitation by a small amount in approaches like SERDS can isolate the Raman scatter from other spectral artifacts and reduce the false detection rate. For example, an input excitation sequence can be correlated with the response of an individual pixel of a detector. From this, pixels that have captured Raman scattered photons can be separated from pixels capturing non-Raman photons. These techniques can be expanded to other fields and/or types of spectroscopies that utilize a dispersive element detector with time-dependent spectral features.