Nanosecond Laser-based Flame Excitation

The flame signal generation module is schematically depicted in Fig. S1a. A Q-switched Nd:YAG nanosecond laser (AT Laser, GlobalCure) with 15 ns pulse full-width-at-half-maximum (FWHM), 4 Hz repetition rate, and ~ 5 mm beam diameter is used as the light source. It offers output options of 1064 nm and 532 nm (second harmonic). A concave lens of f = 50 mm BEL1 (Thorlabs, LC1715) and a convex lens of f = 200 mm BEL2 (Thorlabs, LA1708) are used to expand the output beam. An f = 500 mm cylindrical lens CyL (Thorlabs, LJ1144RM) generates a laser sheet of thickness ~ 400 µm inside the kerosene flame. The burner is mounted on a translation stage so that the laser sheet can excite different positions of the flame. A half-waveplate HWP (Thorlabs, WPH10M-1064 for 1064 nm and WPH10M-532 for 532 nm) and a linear polarizer P1 (Thorlabs, GL15) are used to adjust the laser fluence. The laser sheet is polarized along the y direction. The reflected light from a 10:90 (R:T) beam splitter BS1 (Thorlabs, BS025) is picked by a power meter for laser fluence measurement.