We have successfully developed technology, using an InGaAsP semiconductor laser diode (LD), to simplify water detection.
Based on the observation that the light absorption spectra (in water) peaks at different wavelengths, we measured the light absorption spectra (in water) around one of the peak wavelengths, using a LD and an LED. The results of our measurements are shown below.
These results indicate that simple ways of detecting water were possible with the use of light sources, with the same wavelength as the water wavelength. Furthermore, it was observed that the LD light emission spectra were within the narrow range, including the spectral peak, while the LED light emission spectra spread to a broader range. This indicates that the LD is better suited as a light emission source for detecting water.
Thus, by applying this technology to sensors, we have developed sensors that are as simple as photoelectric switches. They are capable of detecting water contained within materials that the typical water detector cannot do reliably.