to excitation wavelength f1 is shown to be of interest at two response wavelengths r1 r2 the target 39 s response to excitation wavelength f2 is shown to be of interest at two response wavelengths r3 r4 the target 39 s response to excitation wavelength f3 is shown to be of interest at two response wavelengths r5 r6 the response wavelengths of interest can be chosen based on the spectral responsiveness of the target material for example wavelengths characteristic of changes in target material properties can be used examples of suitable wavelengths for selected target materials are discussed in 34 study of the fluorescence properties of normal and neoplastic human cervical tissue 34 mahadevan et al lasers in surgery and medicine 13 647 655 1993 incorporated herein by reference the intensity of the target 39 s response to excitation wavelength f1 at response wavelength r1 is shown as response signal intensity s1 the response at response wavelength r2 is shown as response signal intensity s2 the greater amplitude of signal intensity s2 relative to signal intensity s1 indicates that the target response to excitation wavelength f1 was greater at response wavelength r2 than at response wavelength r1 the response to excitation wavelength f2 at response wavelengths r3 r4 is shown as response signal intensities s3 s4 respectively the target had almost no response at response wavelength r4 the response to excitation wavelength f3 at response wavelengths r5 r6 is shown as response signal intensities s5 s6 respectively the target had a very strong response at response wavelength r6 the excitation and response wavelengths can be chosen to examine particular properties of the target the response signal intensities si can then be.