Multi mode fibre perturber

A gas sensor comprising:

• a quantum cascade chirped laser that outputs a wavelength chirp for providing a wavelength scan;
• a multi-mode fiber positioned between said laser and a target area and having a first end optically coupled to said laser, wherein said multi-mode fiber is configured for transmitting light from the laser to and/or from the target area for sensing a gas located at the target area;
• a randomizer adjacent said multi-mode fiber for randomizing spatial modes supported by the multi-mode fiber;
• a detector spaced apart from said target area for detecting light emitted from a second end of said multi-mode fiber and that has passed through the target area, wherein said detector is configured to average out randomized spatial modes to recover a single spatial mode.

A method for sensing a gas, said method comprising:

• transmitting light from a single mode laser, wherein the laser is a quantum cascade chirped laser that outputs a wavelength chirp for providing a wavelength scan;
• directing the light from the laser at a multi-mode fiber positioned between the laser and a target area and having a first end optically coupled to the laser, wherein the multi-mode fiber is configured for transmitting light from the laser to and/or from the target area for sensing a gas located at the target area;
• randomizing spatial modes supported by the multi-mode fiber using a randomizer adjacent said multi-mode fiber;
• and
• averaging out randomized spatial modes to recover a single spatial mode using a detector spaced apart from said target area for detecting light emitted from a second end of said multi-mode fiber and that has passed through the target area.