Review of elementary electrodynamics and relation between spectroscopy and light induced polarization.

Introduction to open quantum systems and their interaction with coherent light.

Brief review of optical absorption and emission spectrum.

Theoretical construction of spectroscopic signals. Response functions, Green functions in Liouville space, Liouville pathways, double-sided Feynman diagrams.

Review of experimental methods: Transient absorption, spatial coherence, rephasing, photon echo, spectral hole burning, multi-dimentional spectroscopy.

Models of fluctuation dynamics, Brownian oscillator, spin-boson model, stochastic models.

Introduction to recent problems in non-linear spectroscopy.

The lecture forms a unified theoretical ground for interpretation of non-linear spectroscopies and introduces the student into its recent applications in biophysics and chemical physics.