Method and apparatus for the monitoring and control of combustion

A method of sensing a combustion process comprising:

• providing laser light at multiple select lasing frequencies;
• multiplexing the laser light;
• transmitting the multiplexed laser light in a pitch side optical fiber to a process location;
• projecting the multiplexed laser light through a combustion process;
• receiving the multiplexed laser light in a catch side optical fiber;
• demultiplexing the multiplexed laser light;
• and
• transmitting a frequency of demultiplexed laser light to a detector.

An echelle grating based diode laser spectroscopy gas sensing apparatus comprising:

• more than one diode lasers having select lasing frequencies;
• an input echelle grating optically coupled to the diode lasers, the input echelle grating having a select line spacing and a select blaze angle providing for the multiplexing of laser light at the select lasing frequencies;
• an optical fiber having a proximal end optically coupled to the echelle grating to receive multiplexed laser light from the echelle grating;
• a pitch optic optically coupled to a distal end of the optical fiber, the pitch optic being operatively associated with a process chamber and oriented to project laser light through the process chamber;
• an output echelle grating in optical communication with the pitch optic, the output echelle grating having a select line spacing and a select blaze angle providing for the demultiplexing of laser light at the select lasing frequencies;
• and
• a detector sensitive to one of the select lasing frequencies optically coupled to a corresponding demultiplexed lasing frequency.

A method of sensing a combustion process comprising:

• providing laser light at multiple select lasing frequencies;
• multiplexing the laser light with an echelle grating;
• projecting the multiplexed laser light through a combustion process;
• demultiplexing the multiplexed laser light with an echelle grating;
• and
• transmitting a frequency of demultiplexed laser light to a detector.

A pitch side optical system for use in diode laser spectroscopy comprising:

• more than one diode laser having a select lasing frequency, each diode laser being coupled to a proximal end of a distinct input optical fiber;
• a multiplexer optically coupled to a distal end of fewer than all of the input optical fibers, the multiplexer optically coupling multiplexed laser light from the fewer than all of the input optical fibers to a proximal end of a pitch side optical fiber;
• a coupler optically coupled to a distal end of the pitch side optical fiber and a distal end of an un-multiplexed input optical fiber, the coupler optically coupling multiplexed laser light from the pitch side optical fiber and un-multiplexed laser light from the un-multiplexed input optical fiber to a proximal end of a transmission optical fiber;
• and
• a pitch optic optically coupled to a distal end of the transmission optical fiber.

A diode laser spectroscopy gas sensing apparatus comprising:

• a diode laser having a select lasing frequency;
• a pitch optic optically coupled to the diode laser, the pitch optic being operatively associated with a process chamber and oriented to project laser light along a projection beam through the process chamber;
• a catch optic in optical communication with the pitch optic to receive the laser light projected through the process chamber;
• an optical fiber optically coupled to the catch optic;
• a catch side alignment mechanism operatively associated with the catch optic providing for the alignment of the catch optic with respect to the projection beam to maxamize a quantity of laser light received by the catch optic from the pitch optic and coupled to the optical fiber;
• and
• a detector sensitive to the select lasing frequency optically coupled to the optical fiber.

A method of aligning a diode laser spectroscopy gas sensing optical system comprising:

• providing an alignment beam of light;
• projecting the alignment beam through a process chamber;
• receiving the alignment beam with a catch optic, the catch optic being operatively associated with the process chamber;
• optically coupling the alignment beam from the catch optic to a detector through an optical fiber;
• determining the strength of the alignment beam coupled from the catch optic to the optical fiber;
• and
• aligning the catch optic to maximize the strength of the alignment beam coupled from the catch optic to the optical fiber.

A method of sensing NO in a combustion process with tunable diode laser absorption spectroscopy comprising:

• providing laser light at a wavelength of approximately 670 nm;
• transmitting the laser light in a pitch side optical fiber to a gas process location;
• projecting the laser light through a gas process;
• receiving the laser light in a catch side optical fiber;
• transmitting the laser light in the catch side optical fiber to a detector;
• generating a signal from the detector related to the laser light transmitted to the detector;
• calculating a NO2 concentration from the signal;
• and
• determining a NO concentration from the NO2 concentration.