Dual-comb thin-disk oscillator

Abstract

Dual-comb spectroscopy (DCS) normally operates with two independent, relatively low power and actively synchronized laser sources. This hinders the wide adoption for practical implementations and frequency conversion into deep UV and VUV spectral ranges. Here, we report a fully passive, high power dual-comb laser based on thin-disk technology and its application to direct frequency comb spectroscopy. The peak power (1.2 MW) and the average power (15 W) of our Yb:YAG thin-disk dual-comb system are more than one-order-of-magnitude higher than in any previous systems. The scheme allows easy adjustment of the repetition frequency difference during operation. Both combs share all cavity components which leads to an excellent mutual stability. A time-domain signal recorded over 10 ms without any active stabilization was sufficient to resolve individual comb lines after Fourier transformation.

Fig. 1. Schematic drawing of the dual-comb thin-disk laser system.

a The laser is based on the Yb:YAG thin-disk resonator. The beam-paths corresponding to the “red” and “blue” beams are separated in tangential plane for illustration only. EM end mirror, ROC radius of curvature, OC output coupler (10 % transmission). b The heterodyne detection setup. DAQ data acquisition board, FT Fourier transform. c Image of the pump spot (laser active area) on the thin disk. Both laser modes share a single pump spot and therefore a single pump laser. They show a slight horizontal displacement that is a result of the optimized alignment.

Fig. 2. Spectral characteristics of the emitted pulses.

In black, the spectrum of “top pulses”, marked with red circle in Fig. 1c, is displayed. In red, the spectrum of “bottom pulses”, marked in Fig. 1c with a blue circle, is shown.

Fig. 3. Temporal stability of the repetition rates and the difference in the repetition rates.

Both repetition frequencies monotonically decrease with time (black and red curves).

Fig. 4. Measurements with the dual-comb system without any sample.

a Time-trace with 11 consecutive interferograms. Time separation between neighboring interferograms is 7.8 ms. b Single interferogram from center in (a). c FFT spectrum retrieved from a single 20 µs time-trace shown in (b) and OSA reference spectrum. The spectral features (Kelly sidebands) around 1012 and 1052 nm are reproduced very well that confirms accuracy for a spectral span of $\mathrm{\Delta }\lambda =40\mathrm{nm}$.

Fig. 5. Dual-comb spectra before and after applying the correction.

a Apodized (orange) and not corrected (black) spectra transformed from a 312 ms time trace. Forty interferograms contributed in both cases. It is clearly seen that $\mathrm{\Delta }{f}_{\mathrm{rep}}$ jitter-corrected spectrum experiences a significant decrease in noise. The inset shows the frequency comb lines of both spectra. b $\mathrm{\Delta }{f}_{\mathrm{rep}}$ jitter-corrected and apodized spectrum and uncorrected reference.

Fig. 6. Comb line structure of the optical spectrum.

The inset shows a single comb line with FWHM of 3.1 Hz in radio frequency domain.

Fig. 7. Comparison of the Fabry–Pérot etalon spectrum measured with the OSA and dual-comb setup.

The dual-comb spectrum was obtained from a single 80 µs interferogram time-trace. The width of the transmission line is 24 GHz.

Fig. 8. Acetylene spectroscopy.

a A 20 µs time trace with main interferogram and decay oscillations induced by acetylene is shown. b Spectra of a single interferogram (black) and reference spectrum (turquoise, Yokogawa OSA) are displayed.