Dual-frequency-comb UV spectroscopy with one million resolved comb lines

We present high-resolution dual-comb spectroscopy across two broad UV spectral regions spanning 372–410 nm and 325–342 nm. This is achieved by generating sixth and seventh harmonics, respectively, from a low-noise 2.35 µm Cr:ZnS dual-comb laser system. The sixth harmonic band contains approximately 1,000,000 spectrally resolved comb lines, while the seventh harmonic band—around 550,000 comb lines. With the line spacing of 80 MHz, this corresponds to a resolving power of up to 10 million, offering remarkable spectral resolution.