The chapter discusses the development of a dual-comb spectrometer by Fraunhofer IPM, which bridges the gap between Fourier-Transform-IR (FTIR) and Quantum/Interband-Cascade-Lasers (QCL/ICL) spectrometers. This spectrometer combines the advantages of both systems, offering high sensitivity and spectral bandwidth. **Principle of Dual-Comb Spectroscopy:** - Frequency combs emit a large number of coherent and equally spaced modes. - By superimposing two synchronized combs with slightly different spacing, the full optical information is encoded into a radio frequency signal, easily measured with a single photodetector. - Combs with large mode spacing (tens to hundreds of GHz) are used for solids and liquids, while narrow-spaced lines (hundreds of MHz) are used for high-resolution molecular spectroscopy and gas analysis. **System Components:** - **Dual-Comb Generator:** A single continuous-wave laser at 1.55 μm is split into two beams, initialized via electro-optic modulation at slightly different frequencies. - **MIR-Converter:** The near-infrared comb is transferred to the mid-infrared (MIR) range using difference-frequency mixing with an optical parametric oscillator (OPO), covering the wavelength range between 3 and 5 μm. **Versatility and Flexibility:** - The system can measure a wide range of infrared-active gas species in the MIR range (3 to 5 μm). - It offers full control over measurement parameters, including rapid acquisition, spectral resolution, and averaging time spans. - Applications include rapid combustion analysis, process control, gas mixture certification, exhaust gas analysis, and the determination of carbon isotopes in greenhouse gases. **Applications:** - Rapid combustion analysis - Fine-tuned process control - Gas mixture certification - Exhaust gas analysis (N₂O and CO₂) - Determination of carbon isotopes in CO₂ and CH₄ - Multi-component atmospheric monitoring - Characterization and quantification of contaminants in hydrogen (H₂) The dual-comb spectrometer is a versatile tool suitable for various measurement tasks and can be used for prototyping, referencing, and developing spectroscopic methods and systems.The chapter discusses the development of a dual-comb spectrometer by Fraunhofer IPM, which bridges the gap between Fourier-Transform-IR (FTIR) and Quantum/Interband-Cascade-Lasers (QCL/ICL) spectrometers. This spectrometer combines the advantages of both systems, offering high sensitivity and spectral bandwidth. **Principle of Dual-Comb Spectroscopy:** - Frequency combs emit a large number of coherent and equally spaced modes. - By superimposing two synchronized combs with slightly different spacing, the full optical information is encoded into a radio frequency signal, easily measured with a single photodetector. - Combs with large mode spacing (tens to hundreds of GHz) are used for solids and liquids, while narrow-spaced lines (hundreds of MHz) are used for high-resolution molecular spectroscopy and gas analysis. **System Components:** - **Dual-Comb Generator:** A single continuous-wave laser at 1.55 μm is split into two beams, initialized via electro-optic modulation at slightly different frequencies. - **MIR-Converter:** The near-infrared comb is transferred to the mid-infrared (MIR) range using difference-frequency mixing with an optical parametric oscillator (OPO), covering the wavelength range between 3 and 5 μm. **Versatility and Flexibility:** - The system can measure a wide range of infrared-active gas species in the MIR range (3 to 5 μm). - It offers full control over measurement parameters, including rapid acquisition, spectral resolution, and averaging time spans. - Applications include rapid combustion analysis, process control, gas mixture certification, exhaust gas analysis, and the determination of carbon isotopes in greenhouse gases. **Applications:** - Rapid combustion analysis - Fine-tuned process control - Gas mixture certification - Exhaust gas analysis (N₂O and CO₂) - Determination of carbon isotopes in CO₂ and CH₄ - Multi-component atmospheric monitoring - Characterization and quantification of contaminants in hydrogen (H₂) The dual-comb spectrometer is a versatile tool suitable for various measurement tasks and can be used for prototyping, referencing, and developing spectroscopic methods and systems.