Experimental evidence of a strange nonchaotic attractor in a Nd:YVO4 laser with saturable absorber

The diode-pumped Nd: Vanadate laser is one of the most widely used lasers in the near-infrared range. Using passive Q-switching with a Cr:YAG saturable absorber (SA), it generates nanosecond pulses at tens of kilohertz. This laser is known to exhibit low-dimensional deterministic chaos. In this letter, we present experimental evidence of a strange nonchaotic attractor (SNA). SNAs exhibit complex dynamical behavior that is neither periodic nor chaotic, making them difficult to detect in real-world systems. They are typically observed in systems modeled by equations and arise through a route to chaos. By experimentally obtaining time series of two laser variables, we reconstruct the underlying attractor. For a certain position of the SA, we find that all Lyapunov exponents are negative and that the energy spectra exhibit a broad frequency range, indicating that the attractor is nonchaotic and lacks periodicity. Using Higuchi's method, we estimate the fractal dimension df and find that 13% of the nonchaotic time series exhibit a well-defined non-integer df, confirming the presence of an SNA. To the best of our knowledge, this is the first experimental observation of a strange nonchaotic attractor in a complex optical system.