Abstract: A free-space optical communication system includes a transmitter and a receiver, the transmitter being configured to transmit an encrypted message to the receiver at the mid-infrared domain, the transmitter comprising a master mid-infrared optical source configured to generate a mid-infrared signal and a chaos generator configured to generate a chaotic signal by applying external optical feedback to the master mid-infrared optical source, the transmitter being configured to determine an encrypted message from an original message by applying a message encryption technique to the original message and to send the encrypted message to the receiver through an optical isolator, the receiver comprising a slave mid-infrared optical source similar to the master mid-infrared optical source the slave mid-infrared optical source being configured to recover the chaotic signal from the encrypted message by applying chaos synchronization, the receiver further comprising a first detector configured to detect the encrypted me

Abstract: A photo-acoustic gas sensor using a method for modulating the wavelength of the laser radiation, the modulation being obtained via judicious use of an electric current, called the generation current, which pumps the one or more laser sources, and is configured to cause the one or more laser sources to operate in pulsed mode, and of a current, called the base current, which takes non-zero values between each laser pulse with a lower magnitude than the magnitude of the generation current, the magnitude of base current being modulated so that the one or more laser sources emit, into the cell, light radiation having a wavelength that varies periodically about a central wavelength so as to take, at regular intervals, a value specifically suitable for the excitation of a gas to be detected, whereby an interaction between the light radiation and the gas to be detected contained in the cell induces the generation of acoustic waves at a resonant frequency of the cell.