Holography¹ has always held special appeal as it is able to record and display spatial information in three dimensions^2–10. Here we show how to augment the capabilities of digital holography^11,12 by using a large number of narrow laser lines at precisely defined optical frequencies simultaneously. Using an interferometer based on two frequency combs^13–15 of slightly different repetition frequencies and a lensless camera sensor, we record time-varying spatial interference patterns that generate spectral hypercubes of complex holograms, revealing the amplitudes and phases of scattered wave-fields for each comb line frequency. Advancing beyond multicolour holography and low-coherence holography (including with a frequency comb¹⁶), the synergy of broad spectral bandwidth and high temporal coherence in dual-comb holography opens up novel optical diagnostics, such as precise dimensional metrology over large distances without interferometric phase ambiguity, or hyperspectral three-dimensional imaging with high spectral resolving power, as we demonstrate with molecule-selective imaging of an absorbing gas.

We demonstrate nonlinear compression of pulses at 1.03 µm and repetition rate of 200 kHz generated by a ytterbium fiber laser using two cascaded all-solid-state multipass cells. The pulse duration has been compressed from 460 to 22 fs, corresponding to a compression factor of ∼21. The compressed pulse energy is 15.6 µJ, corresponding to an average power of 3.1 W, and the overall transmission of the two compression stages is 76%. The output beam quality factor is M² ∼1.2 and the excess intensity noise introduced by nonlinear broadening is below 0.05%. These results show that nonlinear pulse compression down to ultrashort durations can be achieved with an all-solid-state approach, at pulse energies much higher than previously reported, while preserving the spatial characteristics of the laser.

Time-resolved near-infrared absorption spectroscopy of single non-repeatable transient events is performed at high spectral resolution with a dual-comb interferometer using a continuous-wave laser followed by a single electro-optic amplitude modulator. By sharing high-speed electrical/optical components, our spectrometer greatly simplifies the implementation of dual-comb spectroscopy and offers a high mutual coherence time, measured up to 50 s, without any active stabilization system and/or data processing. The time resolution is as short as 100 µs in our experimental demonstration. For a span of 36 GHz, the mean signal-to-noise ratio of 80, at 100-MHz spectral resolution and 100-µs measurement time, enables precise determination of the parameters of rovibrational lines, including intensity or concentration.

We report on an in-band-pumped Dy-doped ZBLAN fiber laser with tunable emission wavelength in the mid-IR range from 2.925 to 3.250 $\mu$ m and single-frequency operation. Using the combination of an intracavity germanium etalon and a reflective diffraction grating, we demonstrate the selection of single-frequency operation with emission linewidth narrower than 110 kHz, maximum output power of $\sim 40$ mW, and relative intensity fluctuations at a level of 0.9% over an integration bandwidth from 1 Hz to 10 MHz.

We report on absolute measurements of saturated-absorption line-center frequencies of room-temperature trifluoromethane using a quantum cascade laser at 8.6 μm and the frequency modulation spectroscopy method. Absolute calibration of the laser frequency is obtained by direct comparison with a mid-infrared optical frequency comb synthesizer referenced to a radio-frequency Rb standard. Several sub-Doppler transitions falling in the ${\upsilon }_5$ vibrational band are investigated at around $1158.9{\mathrm{cm}}^{-1}$ with a fractional frequency precision of $8.6·{10}^{-12}$ at 1-s integration time, limited by the Rb-clock stability. The demonstrated frequency uncertainty of $6.6·{10}^{-11}$ is mainly limited by the reproducibility of the frequency measurements.