M.Sc Thesis

M.Sc StudentOren Gilad
SubjectExperimental Study of Condensation and Phase-Transition
Phenomena in Actively Mode-Locked lasers
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Baruch Fischer
Full Thesis textFull thesis text - English Version


This work deals with actively mode-locked (AML) lasers as a new light system paradigm in statistical-mechanics using noise as the temperature-analogue. By this point-of-view, we demonstrated two new important phenomena with actively mode-locked (AML) lasers:

1.      High dimensional mode systems (“mode hyper-combs”) which are physical realizations of the Spherical-model (a solvable variant of the Ising model), and show a ferromagnetic-like phase-transition in a magnetic spin systems.

2.      Condensation in a many-pulses AML laser system in a “modulation-trap”, which is a classical analogue of the quantum Bose-Einstein Condensation (BEC) in a potential-trap.

In the first part we present a realization and first experimental results of a conceptual high-dimensional laser mode lattices (laser hyper-combs). They are constructed from regular 1-dimensional combs by multi-frequency modulation in active mode-locking (AML). The hyper-comb, with near neighbor mode interaction and noise functioning as temperature, is mapped to interacting magnetic spin-lattices in the Spherical-model, which is one of the few statistical-mechanics systems soluble in all dimensions. Such systems have in dimensions larger than two (d>2), a phase-transition to a global phase-locked comb. Such lasers can have unique properties for generating short pulses compared to regular AML, by capturing very broad frequency bandwidths. Additionally, the hyper-combs can serve as a rare physical realization of the Spherical-model in any dimension. We report on experimental results demonstrating a ferromagnetic-like phase transition in "three-dimensional" AML.

In the second part we present a laser condensation (LC) phenomenon. It is based on weighting the modes in a loss-gain scale rather than in the energy in quantum BEC. As BEC in one-dimensional system, the LC can be achieved in a fiber laser only with a potential-trap analogue. The loss “trap” in the light pulse system is realized using a special modulation with a power-law dependence. The condensation occurs when the (power-law) exponent is smaller than one (η<1). In the experiments that verified the prediction we varied the noise (“temperature”) for various exponents, and observed the condensation transition for η<1.