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29 September 2000Second harmonic emission and the optical excitation of small particles
At high levels of optical excitation, local coherence in particles or ordered domains within mesoscopically disordered materials can lead to second harmonic emission whose temporal signature characterizes the decay kinetics of the excited state population. Examples of such systems include colloids, cell and membrane suspensions, and many plastics, glasses and other modern materials. The effect is prominent in frequency regions where the second order optical nonlinearity is dominated by transitions involving one particular electronic excited state, and where a two- level model closely models the optical response. With ultrafast pulsed excitation of sufficient intensity to elicit the onset of saturation, second harmonic emission on throughput of a subsequent probe beam exhibits a characteristic decay and recovery. Detailed calculations show that such features also arise in systems whose optical response involves more than two levels.
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David L. Andrews, Luciana Davila-Romero, "Second harmonic emission and the optical excitation of small particles," Proc. SPIE 4098, Optical Devices and Diagnostics in Materials Science, (29 September 2000); https://doi.org/10.1117/12.401640