A team of scientists from the Max Planck Institute of Quantum Optics and Ludwig-Maximilians-Universität Munich (Germany), the Laboratoire Interdisciplinaire Carnot de Bourgogne (France) and the Institut des Sciences Moléculaires d’Orsay (France) report a promising new technique for high-speed and accurate near infrared spectroscopy in Nature Photonics. They use modulators and a non-linear optical fibre to produce two frequency combs, each with more than a thousand evenly spaced infrared spectral lines with a remarkably flat intensity distribution. Line spacing and spectral position can be selected quickly and freely by simply dialling a knob. Such frequency-agile optical combs offer unprecedented freedom when interrogating a molecular spectrum via a powerful technique called multiplexed dual-comb spectroscopy. Two mutually coherent combs are combined in an interferometer. High refresh rates (80 kHz) and tuning speeds (10 nm s–1) at high signal-to-noise ratio are achieved. Such a unique combination holds much promise for trace gas sensing. “Furthermore, the frequency-agile frequency comb generator might also become an enabling tool for applications beyond spectroscopy, like for arbitrary waveform generation, radio-frequency photonics, optical coherence tomography or microscopy”, concludes Dr Ming Yan, a post-doc working at the experiment.