We have demonstrated audio communications with a mid-IR laser. The laser is a frequency doubled Q-switched CO₂ system producing approximately 12ns pulses at 4.6μm. The audio signal was encoded on the beam by means of pulse frequency modulation (PFM) with a carrier frequency of 37kHz. A 1mm diameter, low noise thermoelectrically cooled IR photovoltaic detector with electrical bandwidth 250MHz was used to detect the laser beam. A custom-built circuit stretched the resultant electrical pulses to approximately 1.5μs, before being demodulated. High quality audio signals were received and recorded, and still images were successfully transmitted using slow scan television techniques. The demonstration was conducted at the Defence Science & Technology Organisation's laser range at Edinburgh, South Australia in July 2008. The distance was 1.5km, with a slant path (8m to 1.5m). The maximum range using this system is estimated to be tens of kilometres.

Date Published: 2 October 2008
PDF: 9 pages
Proc. SPIE 7115, Technologies for Optical Countermeasures V, 71150I (2 October 2008); doi: 10.1117/12.803579

Published in SPIE Proceedings Vol. 7115:
Technologies for Optical Countermeasures V
David H. Titterton; Mark A. Richardson, Editor(s)