Quantum Cascade Laser Based Key Technology Of Gas Spectroscopy Detection

Due to the characteristics of high output power, narrow line-width, roomtemperature operation and so on, Quantum Cascade Lasers (QCLs) have become theresearch focus in the fields of trace gas detection technology and instrumentalintegration system.This thesis aimed at the issues existed in the gas detection technology andinstrument system researching, key technologies in gas spectroscopy detectiontechnology based on Quantum Cascade Laser were carried out. And also importantlyfocused on the fundamental theory of quantum cascade laser based spectrum scanningmethod by applying a pulse current to the QCL, and also different spectral ranges wereobtained by tuning the QCL operation temperatures; Research work of theory andrealization methods were also carried out by analysing differential optical absorptionspectroscopy and technology based on F-P etalon, then design and set-up the gasdetection experimental system based on quantum cascade laser, and measured thesystem stability and other characteristics; Take methane (CH4) and formaldehyde(H2CO) as the detection gases, firstly simulated their spectrum using HITRAN andPGOPHER, then calculated the relative parameters and results. Testing measurementsresults showed that the quantum cascade laser based gas spectroscopy detection systemhas a relatively high detection sensitivity and resolution. Absorption line intensity,pressure broadening and pressure induced frequency shift parameters of formaldehyde(H2CO) were measured using the system and good results were obtained.The mainly research works in this thesis were:①Gas detection technology status, existing matters were compared and analysedin this thesis and them gas spectroscopy detection system and realization method wereproposed, the research scheme was confirmed as pulsed distribute feedback quantumcascade laser based gas detection system and technology.②Spectrum scanning theory and methods were researched based on distributefeedback quantum cascade laser, and analysis works were carried out by using pulsecurrent tuning method.③Based on the molecular absorption specificity, fundamental knowledge andmethod were researched based on quantum cascade laser system; by utilizing the gasdetection technology, noise from the environment and other absorptive gases absorption were deducted, and then the sensitivity would be improved. Frequency calibration wasdone by analysing the F-P etalon signal recorded from the experimental system.④Design scheme was proposed as distribute feedback quantum cascade laserbased gas spectroscopy detection, then each functional modal was tested and set-up,then the whole experimental system was done. Spectral range, resolution, absorbancerepetition, stability and detection limit were measured based on this system;⑤Take methane (CH4) and formaldehyde (H2CO) as the detection gases, theirspectra were recorded and analysed, then compared with the HITRAN and PGOPHERsimulation, and spectrum parameters were calculated.⑥Specially, detection work of H2CO was done by measuring its absorption lineintensity, pressure broadening coefficient, pressure induced frequency shift and theRapid Passage effect, and the corresponding results were calculated and analysed.⑦The thesis conclusion was done, and then bring forward the existent matters andconsiderations for the future work.