Design of an analyzer based on a quantum cascade laser for substance identification by infrared reflected radiation

We consider a setup designed to study infrared radiation reflected from liquid and solid substances located on various substrates in this work. We describe the optical and principal scheme for the experimental setup. We use a laser setup that contains one Alpes Lasers quantum-cascade laser chip with a tuning range 1000 - 1300 1/cm with peak power up to 480 mW and 1 MHz repetition rate. Setup includes two HgCdTe thermoelectrically cooled sensors as reference and signal detector. Each sensor is equipped TEC controller, and the amplifier is mounted. The signal is digitized using a 24-bit ADC with a frequency of 1.5 MHz. Measurement time is about 1 sec. Recently experimentally reached sensitivity is less than one microgram per square cm on various substrates. We estimate the device's possible weight to about 5 kg and the sensitivity of about microgram per square cm. This work presents the results of processing the diffuse reflectance spectra. The diffuse reflectance spectra have low selectivity. So, we use calculational algorithms based on Kramers-Kronig transformations with extrapolation of spectra and phase correction. For substance identification using diffuse reflectance spectra, we use database consists of about 20 substances.