English: Original caption: "This technology is known as a Tunable Diode Laser (TDL) gas sensor. The heart of the TDL system is a small laser diode (about 2mm square) that produces a narrow and specific wavelength of light tuned to a harmonic frequency of the water vapor molecule in the near infrared band. The light causes the molecule to vibrate and absorb the energy.

Once adjusted to the specific frequency of the molecule, the laser is minutely tuned to different wavelengths on either side of the target wavelength. By comparing the light energy being absorbed at the water vapor frequency, to the light energy at the surrounding frequencies, a very precise measurement can be made. Multiple measurements are made every second, making the system quick to respond to variations in the target gas.

TDL gas sensing technology is particularly good at detecting low levels of gases at the parts per million or even parts per billion level. With the vast majority of manufactured products relying more and more on gas measurement of some kind, commercial applications for this technique are broad. In every environment from wafer fabrication process control in the semiconductor industry to detecting trace levels of noxious gases in stack emissions, TDLs will be making news in the industrial and environmental monitoring sectors of the economy for years to come."