![spectral comb sound reference signals spectral comb sound reference signals](https://ccrma.stanford.edu/CCRMA/Courses/220a:1998/Lectures/3/Slides/_05a_Spectrum.gif)
The sources that led to the Nobel prize in physics were primarily solid state lasers with repetition rates of few tens of MHz operating in the near infrared. Optical comb sources have evolved tremendously over the last decades (see for an extensive historical overview). We will end with a forward looking overview of the field, touching upon advances in chip scale technology as well as a discussion on what future possibilities lie down the road. Some examples will be shown in the context of the characterization of passive linear components, highlighting the unique features enabled by the comb source. We will cover illustrative arrangements, including low coherence, spectral, and comb calibrated swept frequency interferometry. We begin with a short review of optical frequency comb sources and then give a brief introduction to the basics of spectral interferometry, followed by a discussion on signal characteristics when the broadband source is replaced by a laser frequency comb. In this tutorial paper, we will give an overview of the field of spectral interferometry using laser frequency comb sources. Ĭlose to absorption spectroscopy is linear spectral interferometry where both the amplitude and phase of an optical sample is retrieved from an interferogram signal under the assumption that the optical source is known. Recent efforts in optical frequency-comb based spectroscopy aim at enabling higher acquisition rates in nonlinear spectroscopy, measuring emission (fluorescence) spectroscopy signals, and advance imaging modalities. Frequency combs can also be used as rulers against which to calibrate tunable laser diodes, including noncontinuously tunable ones, and multiple laser diodes can be characterized to cover an ultrabroad bandwidth. Different instruments have been developed over the last decades that are able to resolve the individual comb lines, including high angular dispersive elements, Fourier transform spectrometers with delays matched to the comb’s repetition rate or by multiheterodyne downconversion with another frequency comb that is slightly mismatched in repetition rate. In linear absorption spectroscopy, the uniform grid formed by the comb lines directly probes the specimen under test with a frequency resolution fundamentally limited by the comb linewidth. Indeed, one of the most remarkable applications of frequency combs lies in the field of optical spectroscopy. They have become enabling tools for precision frequency synthesis and metrology. Laser frequency combs are coherent light sources formed by evenly spaced optical frequencies whose location in the electromagnetic spectrum can be set with the accuracy provided by atomic frequency references.