Digitally controlled optical sampling in dual-comb spectroscopy

Dual-comb spectroscopy (DCS) is a powerful method for the characterization of materials. It enables the rapid measurements of broad absorption spectra with high spectral resolution. However, dual-comb spectroscopy has a low duty cycle especially when used to study semiconductor materials whose excited states’ dephasing rates are much shorter than the spacing between the comb pulses. When DCS is applied to these systems, a vast majority of energy and acquisition time is wasted. Here, we demonstrate a simple approach that can aid efforts to solve this issue. In our approach, we use two frequency combs that have the same repetition frequencies and we digitally control the relative locking phase between the combs. This allows us to control the delay with very high precision and take the data rapidly and continuously only in the region where the signal is non-zero. We demonstrate the concept on a Neodymium-doped yttrium orthovanadate (Nd:YVO 4 ) sample. We show that, we could scan the delay between the signal and local oscillator comb pulses up to ∼ 6 ps in under 150 µs. We compare an absorption spectrum of (Nd:YVO 4 ) obtained using our approach to an absorption spectrum obtained using conventional DCS and they are in good agreement. This approach now makes DCS relevant for a wide range of materials.