研究目的
Exploring the feasibility of terahertz laser frequency combs based on quantum cascade lasers in a dual-comb spectroscopy configuration for the detection of multiple molecular samples in the gas phase.
研究成果
The study demonstrates rapid-response QCL-based dual-comb THz measurements of gas mixtures around 3.4 THz, probing an equilibrium reaction of NO2/N2O4 and fast changes in concentrations of NH3 and H2O with a temporal resolution of 1 ms. The main current limitations are related to a noisy cryostat environment and bolometer nonlinearities, with suggestions for future improvements including extending the laser cavity length, broadband QCL gain designs, and advanced dispersion compensation schemes.
研究不足
The main limitations include a noisy cryostat environment and bolometer nonlinearities. Spectral resolution (~17 GHz) and spectral coverage (~180 GHz) could be improved. The system's sensitivity to mechanical vibrations and the need for optical power management or use of Schottky mixers for dual-comb beating are also noted.
1：Experimental Design and Method Selection:
The study employs two THz-QCL OFCs emitting light centered around 3.4 THz, mounted on a cold finger in a cryostat. The setup includes a home-made 14-cm long stainless steel absorption cell with TPX windows for the sample gas mixture. The signal comb interrogates the sample, then combines with the local oscillator comb on a silicon beam splitter, and is detected by a superconducting NbN hot-electron bolometer (HEB).
2：4 THz, mounted on a cold finger in a cryostat. The setup includes a home-made 14-cm long stainless steel absorption cell with TPX windows for the sample gas mixture. The signal comb interrogates the sample, then combines with the local oscillator comb on a silicon beam splitter, and is detected by a superconducting NbN hot-electron bolometer (HEB).
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: The gas mixtures include anhydrous ammonia (NH3), nitrogen dioxide (NO2), dinitrogen tetroxide (N2O4), and water vapor (H2O).
3：List of Experimental Equipment and Materials:
THz-QCL OFCs, cryostat, silicon beam splitter, superconducting NbN HEB, real-time spectrum analyzer (FSW-43, Rohde & Schwarz).
4：Experimental Procedures and Operational Workflow:
The system records the microwave spectrum with an acquisition time of 1 ms per spectra, using a real-time spectrum analyzer. The down-converted THz spectrum shows characteristic beat note amplitude attenuations induced by wavelength-dependent changes in the transmission through the sample cell.
5：Data Analysis Methods:
The resulting microwave spectrum is analyzed for absorbance spectra, with spectral fitting capability demonstrated using a HITRAN simulated mixture model.
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