The non-linear nature of multi-photon fluorescence (FL) excitation, SHG and THG restricts the signal detecting volume to the vicinity of the focal point. As a result, the technology has intrinsic optical sectioning capability. The use of multi-photon fluorescence excitation also allows micro-fluorometry at high spatial resolution. Figure 1 shows a conventional optical micrograph of maize protoplasts, the time lapse fluorescence spectral change from a single chloroplast is shown in FIG 2. Under high intensity illumination, biological specimen not only emits fluorescence, but also generates harmonic emissions. in addition to the Ti-sapphire laser commonly used in multiphoton microscopy, the use of ultra-fast Cr-fosterite laser made simultaneous detecting two- and three-photon fluorescence, SHG and THG possible. in addition to the fluorescence signals generated by multi-photon excitation process, non-linear phenomena such as harmonic generation can also provide useful information about the structure and optical properties of a specimen (Kao et al., 2000). Simultaneous recording the spectral response in an image (x-y-λ) can provide insight about the nature of the signal.