The Raman shift is a characteristic property of a molecule, and the intensity of Raman scattering
is proportional to the density of the molecule. Therefore, gas sensing using Raman scattering can detect and
identify gases. The method is especially useful for detection of hydrogen gas, because the hydrogen
molecule does not have absorption bands from the near ultraviolet to near infrared that can be used for
optical detection using absorption. On the other hand, the hydrogen molecule exhibits a strong Raman
effect, so Raman scattering is a suitable method for hydrogen gas detection. In this chapter, the
fundamentals of Raman scattering, detection of hydrogen gas by Raman scattering, development of lidar
systems for detection, imaging, and concentration measurement of hydrogen gas, are presented. The
concentration of hydrogen gas leaked into the open air can be remotely measured by simultaneous
measurement of the Raman scattering signals from the hydrogen gas and atmospheric nitrogen. Hydrogen
gas leak detection using Coherent Anti-Stokes Raman Scattering (CARS) is also presented.
Keywords: Raman scatttering, coherent anti-stokes raman scattering, raman lidar, raman spectroscopy,
hydrogen gas, imaging, gas concentration, gas flow, shadowgraph, nitrogen.
