A sensing apparatus comprising: more than one diode laser each having a select lasing frequency; a multiplexer (124; 60) optically coupled to more than one but fewer than all of the diode lasers, the multiplexer outputting a multiplexed laser light, the multiplexed laser light being optically coupled to a proximal end of a pitch side optical fiber (126; 66); an input fiber (122n; 66) optically coupled to one diode laser that is not optically coupled to the multiplexer; an optical coupler (130; 134) optically coupled to a distal end of the pitch side optical fiber and a distal end of the input fiber; a transmission fiber optically coupled to the optical coupler; a pitch optic (128; 48) optically coupled to a distal end of the transmission fiber (132; 68), the pitch optic being operatively associated with a combustion chamber (22; 54) and oriented to project a multiplexed laser output through the combustion chamber; wherein wavelengths of the multiplexed laser light range from 1240 nm to 5200 nm and wavelengths of the un-multiplexed laser light are less than 1240 nm; wherein the input fiber (122n; 66) is a single mode fiber; wherein the pitch side optical fiber provides single mode transmission of the multiplexed laser light; wherein the one diode laser light would become multimodal after transmission through the pitch side optical fiber; and wherein the transmission optical fiber is a very short transmission section of multimode fiber that does not allow the higher order spatial modes for the one diode laser light to develop; the sensing apparatus further including: a catch optic operatively associated with the combustion chamber (22; 54) in optical communication with the pitch optic (128; 48) to receive the multiplexed laser output projected through the combustion chamber; a catch side optical fiber optically coupled to the catch optic at a proximal end; a demultiplexer optically coupled to a distal end of the catch side optical fiber, the demultiplexer demultiplexing laser light of each of the select lasing frequencies; and a detector optically coupled with the demultiplexer, the detector being sensitive to one of the select lasing frequencies. more than one diode laser each having a select lasing frequency; a multiplexer (124; 60) optically coupled to more than one but fewer than all of the diode lasers, the multiplexer outputting a multiplexed laser light, the multiplexed laser light being optically coupled to a proximal end of a pitch side optical fiber (126; 66); an input fiber (122n; 66) optically coupled to one diode laser that is not optically coupled to the multiplexer; an optical coupler (130; 134) optically coupled to a distal end of the pitch side optical fiber and a distal end of the input fiber; a transmission fiber optically coupled to the optical coupler; a pitch optic (128; 48) optically coupled to a distal end of the transmission fiber (132; 68), the pitch optic being operatively associated with a combustion chamber (22; 54) and oriented to project a multiplexed laser output through the combustion chamber; wherein wavelengths of the multiplexed laser light range from 1240 nm to 5200 nm and wavelengths of the un-multiplexed laser light are less than 1240 nm; wherein the input fiber (122n; 66) is a single mode fiber; wherein the pitch side optical fiber provides single mode transmission of the multiplexed laser light; wherein the one diode laser light would become multimodal after transmission through the pitch side optical fiber; and wherein the transmission optical fiber is a very short transmission section of multimode fiber that does not allow the higher order spatial modes for the one diode laser light to develop; the sensing apparatus further including: a catch optic operatively associated with the combustion chamber (22; 54) in optical communication with the pitch optic (128; 48) to receive the multiplexed laser output projected through the combustion chamber; a catch side optical fiber optically coupled to the catch optic at a proximal end; a demultiplexer optically coupled to a distal end of the catch side optical fiber, the demultiplexer demultiplexing laser light of each of the select lasing frequencies; and a detector optically coupled with the demultiplexer, the detector being sensitive to one of the select lasing frequencies. a catch optic operatively associated with the combustion chamber (22; 54) in optical communication with the pitch optic (128; 48) to receive the multiplexed laser output projected through the combustion chamber; a catch side optical fiber optically coupled to the catch optic at a proximal end; a demultiplexer optically coupled to a distal end of the catch side optical fiber, the demultiplexer demultiplexing laser light of each of the select lasing frequencies; and a detector optically coupled with the demultiplexer, the detector being sensitive to one of the select lasing frequencies.