The various aspects of embodiment are related to the target chemical/sample of compact and contactless system, method and apparatus for optical detection and are revealed. The wavelength of the different wavelength of light at least two or different frequency bands, and target chemical, at least some of light, therefore there is interaction, at least two photodetectors are incident on target chemical. Each photoelectric detector is configured to detect the wavelength of the different wavelength of light or different frequency bands, this interaction target chemical. Processing logic is configured as the ratio parameter instruction luminous intensity detected between calculating by a photodetector and parameter instruction luminous intensity detected by another photoelectric detector, and the ratio calculated with the target chemical base of determining presence and/or amount.
