An illumination system is disclosed for providing dual-excitation wavelength illumination for non-linear optical microscopy and micro-spectroscopy. The illumination system includes a laser system, an optical splitting means, a frequency shifting system, and a picosecond amplifier system. The laser system includes a laser for providing a first train of pulses at a center optical frequency ω1. The optical splitting means divides the first train of pulses at the center optical frequency ω1 into two trains of pulses. The frequency shifting system shifts the optical frequency of one of the two trains of pulses to provide a frequency shifted train of pulses. The picosecond amplifier system amplifies the frequency shifted train of pulses to provide an amplified frequency-shifted train of pulses having a pulse duration of at least 0.5 picoseconds.