Modulated Laser-Induced Fluorescence

In laser-induced fluorescence (LIF) experiments, laser light with a specific wavelength is used to “pump” molecules into an excited energy level via absorption. A camera or detector is then used to image the fluorescence which occurs as the molecules “relax” to lower energy levels via spontaneous emission. As a result, LIF enables us to visualize where certain chemical species exist (e.g., in a flame) since only specific molecules in the test gas are excited by the laser.

We are currently developing a new LIF technique which employs wavelength- and intensity-modulated laser light to embed specific temporal frequencies in the fluorescence signal. These frequencies can be isolated via signal processing algorithms during post-processing, which enables us to isolate the LIF signal from signal noise, nascent flame emission and other background signals. This is particularly advantageous for infrared-LIF (IR-LIF) combustion diagnostics to avoid the infrared background signals originating from hot flame gases and engine components. The figure below illustrates one of our modulated-LIF techniques which we used to enable infrared planar laser-induced fluorescence imaging of carbon monoxide in a flame.

More information regarding this technique can be found in our manuscript here.