Optical sensor

An optical system for obtaining quantity of hydrogen bonding gaseous molecules, the optical system comprising

• an optically transparent matrix comprising a molecule containing a hydroxyazobenzene group or its derivative embedded in the matrix,
• an isomerizing light source,
• means for measuring absorbance changes from the optically transparent matrix, and
• measurement control electronics arranged to control the isomerizing light source, the means for measuring absorbance changes, and optionally a second light source, wherein the measurement control electronics is arranged to
• illuminate the optically transparent matrix with isomerizing light capable of inducing trans-cis isomerization in the hydroxyazobenzene group or its derivative,
• measure absorbance changes from the optically transparent matrix at a single or multiple wavelength(s) to obtain thermal cis-trans isomerization time constant, and
• obtain the quantity of the hydrogen bonding gaseous molecules by using the dependency of the thermal cis-trans isomerization time constant to the quantity of the hydrogen bonding gaseous molecules.