On the possibility of designing a high-resolution heterodyne spectrometer for near-IR range on the basis of a tunable diode laser

The results of heterodyning of broadband radiation in the near-IR range are presented. A stabilised DFB laser was used as a local oscillator, while the role of a broadband radiation source was played by another DFB laser, excited by the pump current below its threshold value. A fibre-optical Y-coupler based on the single-mode silica fibre served as a diplexer. The radiation mixed in the singlemode fibre was incident on the photodetector, the role of which was played by a p — i — n photodiode. The signal from the photodiode was amplified by the preamplifier with the feedback resistance 240 kΩ and the bandwidth ~1 MHz and then digitised using a 16-digit ADC. The frequency scanning was implemented via the variation of the local oscillator frequency. The developed registration system provides the sensitivity ~1.4 % of the shot noise value at the acquisition time ~40 min.