What is a Fabry-Perot etalon?
Fabry-Perot etalon is a type of optical interferometer that is used to selectively transmit or reflect light of specific wavelengths. It consists of two parallel reflective surfaces separated by a precise distance, typically in the range of micrometers. These surfaces can be made of glass, metal, or other materials that have high reflectivity and low absorption of light. The Fabry-Perot etalon is named after Charles Fabry and Alfred Perot, who invented this device in 1899.
How does a Fabry-Perot etalon work?
A Fabry-Perot etalon works based on the phenomenon of optical interference. When a beam of light enters the etalon, it undergoes multiple reflections between the two reflective surfaces. Depending on the thickness of the etalon and the wavelength of the light, the reflected waves can either constructively or destructively interfere with each other. This interference pattern results in a series of bright and dark fringes, known as Fabry-Perot interference fringes. The wavelength of the transmitted or reflected light can be controlled by adjusting the distance between the two reflective surfaces.
Applications of Fabry-Perot etalon
Fabry-Perot etalons have various applications in optics and photonics, such as:
- Spectroscopy: Fabry-Perot etalons are used to measure the spectrum of light emitted or absorbed by a sample. By tuning the etalon’s thickness, the spectral resolution can be increased, enabling the detection of subtle spectral features.
- Optical filters: Fabry-Perot etalons can be used as narrowband optical filters that transmit only a specific wavelength of light. They are commonly used in telecommunications, imaging, and sensing applications.
- Laser resonators: Fabry-Perot etalons are used as cavity mirrors in laser resonators, which determine the laser’s output wavelength and linewidth.
Example: Fabry-Perot etalon in spectroscopy
In spectroscopy, Fabry-Perot etalons can be used as scanning interferometers to measure the optical spectrum of a sample. The etalon is placed in the path of the light beam, and the distance between the two reflective surfaces is varied by a piezoelectric transducer. As the distance changes, the interference pattern shifts, resulting in a change in the transmitted intensity. By detecting this intensity change and analyzing it using Fourier transform, the spectrum of the sample can be obtained. Fabry-Perot etalons are particularly useful for measuring the spectra of gases, liquids, and thin films, where high spectral resolution is required to distinguish between closely spaced spectral lines.