its broad tunability these characteristics are quite suitable for remote sensing device fig5 shows a thermal lens spectrum 94 of no 2 from 450 to 590 nm each peak corresponds well with previously reported spectra in this experiment the idler was not isolated however absorption of the idler wavelength by the sample was small and so could be neglected since the intensity of the thermal lens input signal 40 is proportional to the opo power intensity variations over the tuning range will affect the amplitude of the spectral peaks this is the reason the peaks under 470 nm are relatively small during a scan over such a wide spectral range dispersion of the focusing lens and the beam splitter influences the signal intensity in this experiment however the confocal distance was estimated to be less than 1 mm over the spectral range the focal point and the focal length changed by less than 0 1 mm and a few millimeters respectively since the direct incidence method was employed these factors had no significant effect on the spectrum fig6 shows the spectrum 96 of the same sample between 600 and 680 nm reproducing exactly the known spectrum of this molecule because no 2 shows a complicated spectrum finer details of the spectrum cannot be resolved at this resolution as the excitation beam is tuned toward the wavelength of the he ne laser it can spuriously give a positive signal at the photomultiplier tube however since.