A
system for generating signals for Raman vibrational analysis, particularly for a CARS
microscope or spectroscope of an external specimen, the
system comprising a a
laser source apt to emit at least one fundamental optical pulse in a first band of fundamental frequencies comprising at least one first (ωf1) and one second (ωf2) fundamental frequencies; a second-
harmonic (SH) generating
system comprising at least one
nonlinear optical crystal for converting said at least one fundamental optical pulse into at least two second-
harmonic optical pulses, i.e. a first second-
harmonic pulse at a first second-harmonic frequency (ωp) of the first
fundamental frequency (ωf1) and a second second-harmonic pulse at a second second-harmonic frequency (ωs) of the second
fundamental frequency (ωf2), said second second-harmonic frequency being other than the first second-harmonic frequency, and a Raman vibrational analysis apparatus apt to receive said first and second second-harmonic pulses and direct them toward said specimen.According to an embodiment, the SH system comprises two
nonlinear optical crystals, each including a
ferroelectric crystal with periodic space-modulation of the sign of the optical susceptibility.In a different embodiment, the SH system comprises a
ferroelectric crystal with aperiodic space-modulation of the sign of
nonlinear optical susceptibility, with a period varying along the
optical path of said at least one fundamental optical pulse, said
crystal being apt to generate said first and second second-harmonic pulses.