General View on Optical Gas Sensing

Korotcenkov, Handbook of Gas Sensor Materials Properties, Advantages and Shortcomings for Applications Volume 1 Conventional Approaches, Integrated Analytical Systems, 

14 Materials for Optical, Fiber Optic, and Integrated Optical Sensors 

Radio frequency range Electron spin causes a very small magnetic dipole  

100 m-1 cm invePing the spin causes a change of the dipole s spatial direction that interacts with the magnetic part of the radiation and leads to absorption or emission 

Microwave range Molecules with permanent polar dipole moment align 

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