This is an optical instrumentation concept for enhancing the spectral sensitivity of interferometers by use of dispersive media, in which the group velocity of light is slowed (slow-light). Conversely, spectrometers can be modified with fast-light dispersive media to reduce the sensitivity, but broaden the measurable spectral range.
The concept for enhancing the spectral sensitivity, or broadening the measurable range, can be realized in interferometers of various types, including sheared-wedge, Mach-Zehnder, Michelson and Fabry-Perot. These devices include spectrophotometers used in bio-medical, chemical, pharmaceutical and astronomical applications, devices for sub-micrometer metrology for non-contact measurements of distance and in optical sensing and quantum information processing applications. The effect can be applied in the UV, visible and IR wavelengths.
The spectral sensitivity of an interferometer is enhanced by a factor which is proportional to the group index of the material in the slow light cell. A slow light medium is one that has a large group index as compared with the index of refraction. Very large group indexes can be achieved in atomic vapors and photonic crystal structures, which may be used as the slow light medium. The concept was reduced to practice using a cadmium-sulfur-selenium single crystal semiconductor as the slow light medium, which provided a spectral sensitivity enhancement of a factor of 2. An enhancement factor of 100 has also been demonstrated in a Fourier transform interferometer. It is possible that the factor could be several orders of magnitude more.