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Abstract Mid-infrared (MIR) spectrometers are invaluable tools for molecular fingerprinting and hyper-spectral imaging. Among the available spectroscopic approaches, GHz MIR dual-comb absorption spectrometers have the potential to simultaneously combine the high-speed, high spectral resolution, and broad optical bandwidth needed to accurately study complex, transient events in chemistry, combustion, and microscopy. However, such a spectrometer has not yet been demonstrated due to the lack of GHz MIR frequency combs with broad and full spectral coverage. Here, we introduce the first broadband MIR frequency comb laser platform at 1 GHz repetition rate that achieves spectral coverage from 3 to 13 µm. This frequency comb is based on a commercially available 1.56 µm mode-locked laser, robust all-fiber Er amplifiers and intra-pulse difference frequency generation (IP-DFG) of few-cycle pulses inχ⁽²⁾nonlinear crystals. When used in a dual comb spectroscopy (DCS) configuration, this source will simultaneously enable measurements with μs time resolution, 1 GHz (0.03 cm⁻¹) spectral point spacing and a full bandwidth of >5 THz (>166 cm⁻¹) anywhere within the MIR atmospheric windows. This represents a unique spectroscopic resource for characterizing fast and non-repetitive events that are currently inaccessible with other sources. 

Mid-infrared microscopy is an important tool for biological analyses, allowing a direct probe of molecular bonds in their low energy landscape. In addition to the label-free extraction of spectroscopic information, the application of broadband sources can provide a third dimension of chemical specificity. However, to enable widespread deployment, mid-infrared microscopy platforms need to be compact and robust while offering high speed, broad bandwidth, and high signal-to-noise ratio. In this study, we experimentally showcase the integration of a broadband, high-repetition-rate dual-comb spectrometer (DCS) in the mid-infrared range with a scanning microscope. We employ a set of 1-GHz mid-infrared frequency combs, demonstrating their capability for high-speed and broadband hyperspectral imaging of polymers and ovarian tissue. The system covers 1000 cm−1 at νc = 2941 cm−1 with 12.86 kHz spectra acquisition rate and 5 µm spatial resolution. Taken together, our experiments and analysis elucidate the trade-off between bandwidth and speed in DCS as it relates to microscopy. This provides a roadmap for the future advancement and application of high-repetition-rate DCS hyperspectral imaging. 

Molecular diagnostics are a primary tool of modern chemistry, enabling researchers to map chemical reaction pathways and rates to better design and control chemical systems. Many chemical reactions are complex, involving multiple species and reaction pathways occurring on µs or shorter timescales. Existing diagnostic approaches provide a subset of chemical and thermodynamic information. Here we optimize across many diagnostic objectives by introducing a high-speed and broadband, mid-infrared dual-frequency-comb absorption spectrometer. The optical bandwidth of >1000cm⁻¹covers absorption fingerprints of many species with spectral resolution <0.03cm⁻¹to accurately discern their absolute quantities. Key to this advance are 1 GHz pulse repetition rate mode-locked frequency combs covering the 3–5 µm region that enable a spectral acquisition rate of 290cm⁻¹per 17.5 µs per detector forin situtracking of fast chemical process dynamics. We demonstrate this system to quantify the abundances and temperatures of each species in the complete reactants-to-products breakdown of 1,3,5-trioxane, which exhibits a formaldehyde decomposition pathway that is critical to modern low-temperature combustion systems. By maximizing the number of observed species and improving the accuracy of temperature and concentration measurements, this spectrometer provides a pathway for modern chemistry approaches such as combining chemical models with machine learning to constrain or predict complex reaction mechanisms and rates. 

We study abundance and temperature of species in reactant to product breakdown of 1,3,5-trioxane inside a shock-tube using a 1 GHz repetition rate mid-infrared dual-comb spectrometer with optical bandwidth > 30 THz. 

We report high-speed measurements of chemical kinetics reactions inside a shock tube using a 1-GHz repetition rate mid-infrared dual-comb spectrometer. We show formation of formaldehyde and sub-sequent decomposition to carbon-monoxide with 17.5 μs time resolution.