Design of matched optical pulses for coherent Raman imaging

Coherent anti-Stokes Raman scattering (CARS) provides information on the Raman spectrum of a sample at greater signal strength than incoherent Raman scattering. The optical pulses are used which excites all vibrational modes of the molecules in the sample over a given bandwidth, but the pulse was conceived so that only a subset of modes would generate CARS signals that interfere constructively at a detector. The optical pulses reduces nonresonant background signal. The pulse design algorithm explicitly constructs an approximation to the matched filter of third-order nonlinear susceptibility in the time domain, subject to constraints of finite time support and realizability given an initial laser pulse spectrum. A heterodyne detection method could be used to further increase the instrument's sensitivity and a reference pulse is specifically shaped to have the form of the emitted CARS signal of a chemical species. The autocorrelation signal predicted from DNA is more than 10 times that of RNA so closely related biochemical species could be distinguished easily.