There is a fig. Two coins are reflected by the train of frequencies of a generator. The wave scattered by the object interfered with the comb at the lensless detector matrix. Credit: DOI
Holography uses a light field without a lens to take pictures. Scientists at the Max-Planck Institute of Quantum Optics are using optical frequencies to move holography forward. holograms over the rainbow can be recorded Each hologram has a three-dimensional image of the scene in which the focusing distance can be chosen. The three-dimensional object is rendered with high precision and no ambiguity by combining all these holograms. The scientists show molecule-selective images of a cloud of ammonia vapor with the help of the frequency combs.
Frequency combs are 3D.
A group of scientists at the Max-Planck Institute of QuantumOptics in Garching, Germany, demonstrate a new technique with optical frequencies.
A regular train of short laser pulse is emitted by an optical frequency comb generator. The spectrum has a large number of comb lines. It is possible to count the wiggles of a light wave with high precision thanks to the frequencies combs. Theodor Hnsch, head of the Laser Spectroscopy Division at the MPQ, won the 2005 Nobel Prize in physics for his invention. The technique of "dual-comb spectroscopy" was developed at MPQ in the group of Nathalie Picqué, using all the lines of a frequency comb and a second laser.
The same interference method is used for hyperspectral digital holograms. The setup seems simple. Edoardo Vicentini, a post-doctoral researcher, explains that it only uses two comb generators of slightly different repetition rates, a partly transmitted mirror, and a fast digital camera sensor without a lens.
A 3D object is illuminated by one of the pulse trains, and the scattered light is directed by the beam-splitter onto the camera sensor. The second pulse train is directed towards the same sensor. The camera records a spatial interference pattern that changes with time, since the two lasers emit theirpulses with varying time separation. A video recording of the interference pattern is shown in a supplemental video.
In traditional holograms, a fine interference pattern is recorded on film, and illumination with a laser beam recreates the original wavefronts from the object. The original scene is reconstructed by a computer program. Two coins are used as objects in an experiment. The focusing distance can be changed so that the coins appear in focus while the other appears blurry, as shown in the video.
Theodor Hnsch was thrilled when he got a program to work that could produce a movie of reconstructed images. The amount of recorded data can become large with a faster camera, so that data processing will become more challenging.
The results of dual-comb interferometers are amazing. The combination of broad bandwidth, long temporal coherence and multi-heterodyne read-out offers powerful new features. New frontiers are likely to be conquered by our technique. It will be exciting to explore its potential for microscopes.
Edoardo Vicentini and his team wrote about dual-comb hyperspectral digital holography. There is a DOI of 10.1038/s41566-021-00892-x.
Nature Photonics is a journal.
There is a news story about three-dimensional image with optical frequencies retrieved fromphys.org on December 2, 2021.
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