Single Image Spectroscopy Using a Grating Spectrometer and a Broadband IR Laser Source

We present recent results from using a quantum cascade laser as a broadband infrared source for real-time spectroscopy. Using a Fabry-Perot quantum cascade laser (FP-QCL), we illuminate samples with broadband IR light from 8.2 mu m to 10.2 mu m. This laser source and its operating conditions (25 degrees C and 500 ns pulses at 200 kHz repetition rate) were chosen to give broad spectral coverage and high power output (42.7 mW average power, pulsed operation). We utilized a simple grating spectrometer together with a high resolution (1280 x 1024 pixel) micro-bolometer focal plane array to capture each full spectrum in a single frame. Several samples were characterized using this apparatus in a transmission-style measurement and their real-time spectra were compared to their Fourier Transform Infrared (FTIR) spectra. The results show a good agreement between FTIR and the real-time grating spectrometer for several representative samples, including bandpass filters, and IR active materials such as polystyrene, polyester, and polypropylene. Finally, we show the real-time benefit of this approach by measuring a moving target foil on a rotating chopper wheel.