Fascinating holography – digital and more powerful than ever
All of us have seen holograms: on bank notes, in passports and in Star Wars! Holography is a powerful 3D photographic technique. Edoardo Vicentini and Nathalie Picqué of the Max Planck Institute of Quantum Optics (MPQ) in Garching have taken holography a step further by coupling it with frequency comb technology. This enables even better 3D imagery with previously unimagined properties and opens up new avenues in optical diagnostics.
An optical frequency comb generator emits a regular train of short laser pulses. Its spectrum consists of a large number of sharp, equally spaced spectral lines that together resemble a comb. Such frequency combs can be used to determine the frequency of light with high precision. For this invention, Theodor Hänsch, who heads the Laser Spectroscopy Division at MPQ, received the Physics Nobel Prize in 2005. Later, the MPQ group headed by Nathalie Picqué developed what is called dual-comb spectroscopy. This technique uses all of the spectral lines of a frequency comb to interrogate a sample over a broad spectral range and combines this with a second frequency comb having slightly difference spacing. The resulting interference pattern is then detected by the team using a fast photodetector.
With its new imaging technique known as hyperspectral digital holography, the group is expanding the application of this interference method to holographic imaging. The basic principle of using two frequency combs remains unchanged, but for holographic applications a camera is employed instead of a photodetector. The camera registers a spatial interference pattern that changes over time since the two lasers emit their pulses at different intervals. A computer calculates the radio frequency spectrum of the interference signal for each pixel. These spectra are then combined in a stack of digital holograms.
Dual-comb interferometers produce breathtaking results in spectroscopy and in ranging applications. The unique combination of broad spectral bandwidth, long temporal coherence and multi-heterodyne readout offers powerful new features for holography. The technique developed by Vicentini and Picqué is likely to conquer new frontiers in scan-free wavefront reconstruction and three-dimensional metrology. Beyond that, it may have potential applications in microscopy for biological samples.
2022 Helmholtz Prize in the category of “Precision Measurement in Applied Metrology”
Dr. Nathalie Picqué, Dr. Edoardo Vicentini For their paper entitled “Dual-comb hyperspectral digital holography”
Scientific publication
N. Picqué, E. Vicentini et al.: Dual-comb hyperspectral digital holography. Nature Photonics 15, 890–894 (2021), doi.org/10.1038/s41566-021-00892-x
Contact
Dr. Nathalie Picqué, Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching, Germany, phone: +49-89 32905-712, e-mail: nathalie.picque(at)mpq.mpg.de
