Coherent combining of fiber-laser-pumped 3.4 μm frequency converters
A. Odier, A. Durécu, J.-M. Melkonian, L. Lombard, M. Lefebvre, and P. Bourdon
Abstract
Coherent beam combining (CBC) by active phase control could be useful for power scaling fiber-laser-pumped optical frequency converters like optical parametric oscillators (OPOs). However, a phase modulator operating at the frequency-converted wavelength would be needed, which is a non-standard component. Fortunately, nonlinear conversion processes rely on a phase-matching condition, correlating not only the wave-vectors of the coupled waves, but also their phases. It is therefore possible to control the phase indirectly, using more standard phase modulators. Feasibility of this technique was previously demonstrated for second harmonic generators (SHG). Controlling the phase of the fundamental wave, excellent harmonic wave combining efficiency was achieved in both cases of phase matching and quasi phase matching, with lower than λ/30 residual phase error. In this paper, coherent combining of difference frequency generators (DFG) is experimentally tested. Even if DFG is more challenging than SHG as it implies handling three waves instead of two, phase control of the sole 1-μm pump waves is sufficient to combine the 3.4μm waves generated.
In this Letter, we demonstrate efficient room temperature detection of ultra-broadband mid-wave-infrared (MWIR) light with an almost flat response over more than 1200 nm, exploiting an efficient nonlinear upconversion technique. Black-body radiation from a hot soldering iron rod is used as the IR test source. Placing a 20 mm long periodically poled lithium niobate crystal in a compact intra-cavity setup (>20 W CW pump at 1064 nm), MWIR wavelengths ranging from 3.6 to 4.85 μm are upconverted to near-infrared (NIR) wavelengths (820–870 nm). The NIR light is detected using a standard low-noise silicon-based camera/grating spectrometer. The proposed technique allows high conversion efficiency over a wider bandwidth without any need for a shorter crystal length. Different analytical predictions and numerical simulations are performed a priori to support the experimental demonstrations.
Coherent frequency combs for spectroscopy across the 3-5μm region
D. L. Maser, G. Ycas, W. I. Depetri, F. C. Cruz, S. A. Diddams
Abstract
A tunable mid-infrared frequency comb was created via difference frequency generation. Pulses between 1 and 1.5 µm were mixed to generate light ranging from 2.6 to 5.2 µm. Two such combs were heterodyned at 5 µm to show their coherence and potential for spectroscopy. The properties of the comb were modeled using numerical simulation, which confirmed the observed bandwidths.
High-coherence mid-infrared dual-comb spectroscopy spanning 2.6 to 5.2 μm
G. Ycas, F. R. Giorgetta, E. Baumann, I. Coddington, D. Herman, S. A. Diddams & N. R. Newbury
Abstract
Mid-infrared dual-comb spectroscopy has the potential to supplant conventional Fourier-transform spectroscopy in applications requiring high resolution, accuracy, signal-to-noise ratio and speed. Until now, mid-infrared dual-comb spectroscopy has been limited to narrow optical bandwidths or low signal-to-noise ratios. Using digital signal processing and broadband frequency conversion in waveguides, we demonstrate a mid-infrared dual-comb spectrometer covering 2.6 to 5.2 µm with comb-tooth resolution, sub-MHz frequency precision and accuracy, and a spectral signal-to-noise ratio as high as 6,500. As a demonstration, we measure the highly structured, broadband cross-section of propane from 2,840 to 3,040 cm−1, the complex phase/amplitude spectra of carbonyl sulfide from 2,000 to 2,100 cm−1, and of a methane, acetylene and ethane mixture from 2,860 to 3,400 cm−1. The combination of broad bandwidth, comb-mode resolution and high brightness will enable accurate mid-infrared spectroscopy in precision laboratory experiments and non-laboratory applications including open-path atmospheric gas sensing, process monitoring and combustion.
