This work was supported by the Special Funds for Ma-jor State Basics Research Project (No. G20000683-2),General Program and Key Program of National Natu-ral Science Foundation (No. 90101002, 60136010), andNational Advanced Materials Committee of China (No.2001AA311140, 2005AA31G040).
The principle of step-scan Fourier transform infrared (FTIR) spectroscopy is introduced. Double modulation step-scan FTIR technique is used to obtain the quantum cascade laser's stacked emission spectra in the time...