Patent ID: 7248755

Claim:
A sensing apparatus comprising: more than one diode laser each having a select lasing frequency; a multiplexer optically coupled to more than one of the diode laser, the multiplexer outputting a multiplexed laser output, the multiplexed laser output being optically coupled to a proximal end of a pitch side optical fiber; a pitch optic optically coupled to a distal end of the pitch side optical fiber, the pitch optic being operatively associated with a process chamber and oriented to project the multiplexed laser output through the process chamber; a catch optic operatively associated with the process chamber in optical communication with the pitch optic to receive the multiplexed laser output projected through the process 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.