A simple method for determination of nonlinear propagation regimes in gases

International audienceA simple method to evaluate the nonlinear propagation regimes in gases is demonstrated. The principle is to focus ultrashort laser pulses into a gas cell, vary the input pulse power and measure the transmission through a pinhole placed at the output. The resulting transmission curve yields an intuitive signature of various nonlinear propagation regimes. Going from low powers to higher, one first observes a brief decrease in the transmission due to nonlinear moving focus. Then, a sharp rise occurs, indicating the starting of the filamentation process. When the power increases further, the transmission saturates and eventually decreases due to the beginning of multi-filamentation. As a result, this method gives a quick and sensitive measurement of pulse energies required to have single and multiple filaments