"We should note that this latter type of shift was successfully amplified to a considerable extent by Russian physicists using the intense light of a ruby laser whose wavelength is close to that of a transition of the potassium atom"

This quote by Alfred Kastler is describing a type of shift in the energy levels of an atom. This shift is brought on by the absorption of light, and Russian physicists had the ability to amplify this shift to a substantial degree by utilizing the extreme light of a ruby laser. The wavelength of the ruby laser was close to the wavelength of a transition of the potassium atom, which permitted the Russian physicists to successfully magnify the shift. This quote highlights the importance of the wavelength of light in the absorption of energy by an atom, and how this can be utilized to magnify the shift in energy levels. It likewise demonstrates the success of Russian physicists in using the ruby laser to magnify the shift. This quote is a testament to the power of light in controling the energy levels of an atom.