We present a novel detection scheme for high-sensitivity spectroscopy in the mid-infrared. We use a low-noise and low-complexity dual-comb source based on a PPLN OPO and an Yb:YAG pump. Both the laser and OPO are spatially-multiplexed single-cavity dual-comb sources. At a repetition rate of 250 MHz and ps-long pump pulses, high power per comb line of >120 W is achieved at 3000 nm (idler). The idler is tunable from 2700 nm to 5170 nm. The system enables comb-line-resolved dual-comb spectroscopy measurements in free-running operation. With our detection scheme, we achieve a spectral coefficient SNR/\sqrt\tau > 10000 \sqrt{Hz} (40 dB) at 3 µm.
KEYWORDS: Optical parametric oscillators, Spectroscopy, Multiplexing, Tunable lasers, Spectral coherence, Signal to noise ratio, Signal generators, Picosecond phenomena, Laser systems engineering, Frequency combs
We present a low-noise and high power per comb line dual-comb source based on a PPLN OPO and an Yb:YAG pump. Both the laser and OPO are spatially-multiplexed single-cavity dual-comb sources. The system operates at a repetition rate of 250 MHz, and the relatively long pump pulse duration of around 900 fs leads to a high power per comb line of >60 μW in the idler at 3500 nm. The idler is tunable from 2900 nm to 4170 nm. The system runs at over 15 kHz repetition rate difference, enabling comb-line-resolved dual-comb spectroscopy measurements in free-running operation.
Single-cavity dual-comb lasers are emerging as new light sources benefiting many applications. Here we demonstrate two new operation regimes for these lasers: a 250-MHz repetition rate 1-ps pulse duration laser, and a 1-GHz 80-fs laser. Each source delivers more than 2 W of average power per comb. Compared to our earlier 80-MHz laser which was limited to 500 Hz, both new lasers can achieve up to 25 kHz repetition rate difference without aliasing. We study the suitability of these lasers for comb line resolved measurements and we show excellent coherence between the pulse trains which enables long-term coherent averaging by computational comb line tracking.
We present a free-running 80-MHz polarization-multiplexed solid-state dual-comb laser which delivers 1.8 Watts of average power with 110-fs pulse duration per comb. We apply this free-running dual-comb laser to picosecond ultrasonic measurements via a high-sensitivity pump-probe setup. We demonstrate ultrasonic measurements on thin-film samples, and compare our measurements to ones obtained with a pair of locked femtosecond lasers and x-ray diffraction measurements. Our data show that a free-running dual-comb laser is well-suited for picosecond ultrasonic measurements and thus it offers significant reduction in complexity and cost for this widely adopted non-destructive testing technique.
We present a new approach for dual-comb optical parametric oscillators. The system uses a single-cavity dual-comb laser that pumps a single OPO cavity. The pump has 1.7 W average power per comb at 1054 nm with 80-MHz repetition rate. The OPO ring cavity is pumped in opposite directions by the two pumps. The idler beams have >280 mW average power at 3500 nm with 145-nm bandwidth. We characterize the signal noise and find shot-noise-limited performance (RIN below -155 dBc/Hz at >1 MHz frequencies). Our approach represents a low-noise solution to dual-comb spectroscopy across the short-wave infrared and mid-infrared spectral regions.
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