Franco Prati
University of Insubria, Como, Italy - franco.prati@uninsubria.itG.J. de Valcarcel, A. M. Perego, J. Redondo
Passive modelocking (PML) is a widespread method used to generate coherent light pulses and optical frequency combs. The basic mechanism of PML has been understood since the fundamental work of Haus based on the master equation (ME) approach [1]. Yet it is known that Haus ME may fail in the common case of a class-B laser where the cavity photon lifetime is shorter than or comparable to the gain recovery time. Here we show how a sound ME for PML in class B lasers can be derived, which is valid for gain and absorption both slow and fast. We start from the hystorical Haus' map and we transform it into a ME in various steps which include a rigorous definition of the slow and fast times that are commonly used in the ME, and the splitting of gain and absorption in slow and fast components [2]. This procedure leads to exact periodic boundary conditions and it is essential to keep the problem simple, both analytically and numerically. The novel ME correctly incorporates gain and absorber dynamics. The stability analysis, confirmed by numerical simulations, allows to determine the parametric conditions for which fundamental modelocking destabilizes to Q-switching modelocking on one side and harmonic modelocking on the other side.
[1] H. A. Haus, IEEE J. Sel. Top. Quant. Electron. 6, 1173-1185 (2000).
[2] A. M. Perego, B. Garbin, F. Gustave, S. Barland, F. Prati, and G. J. de Valcárcel, Nature Commun. 11, 311 (2020).
Franco Prati is associate professor of Physics at the University of Insubria, where he teaches General Physics II (Electromagnetism), Oscillations and Waves, Metamaterials. His main research fields are laser physics and nonlinear optics, and his interests include: optical instabilities, optical pattern formation, dissipative spatial and temporal structures in optical cavities.