Rafi Weill

Critical Behavior of Light in Mode-Locked Lasers

Light is shown to exhibit critical and tricritical behavior in passively mode-locked lasers with externally injected pulses. It is a first and unique example of critical phenomena in a one-dimensional many-body light-mode system. The phase diagrams consist of regimes with continuous wave, driven parapulses, spontaneous pulses via mode condensation, and heterogeneous pulses, separated by phase transition lines that terminate with critical or tricritical points. Enhanced non-Gaussian fluctuations and collective dynamics are present at the critical and tricritical points, showing a mode system analog of the critical opalescence phenomenon. The critical exponents are calculated and shown to comply with the mean field theory, which is rigorous in the light system.

When does single-mode lasing become a condensation phenomenon?

We present a generic route to classical light condensation (LC) in linear photonic mode systems, such as cw lasers, with different grounds from regular Bose-Einstein condensation (BEC). LC is based on weighting the modes in a noisy environment (spontaneous emission, etc.) in a loss-gain scale, rather than in photon energy. It is characterized by a sharp transition from a multi- to single-mode oscillation. The study uses a linear multivariate Langevin formulation which gives a mode occupation hierarchy that functions like Bose-Einstein statistics. Condensation occurs when the spectral filtering has near the lowest-loss mode a power law dependence with exponent smaller than 1. We then discuss how condensation can occur in photon systems, its relation to lasing and the difficulties to observe regular photon-BEC in laser cavities. We raise the possibility that experiments on photon condensation in optical cavities fall in a classical LC or lasing category rather than being a thermal-quantum BEC phenomenon.

Noise-mediated Casimir-like pulse interaction mechanism in lasers

Strongly pumped mode-locked lasers often form pulse bunches. Although several mechanisms of pulse interaction are known, none yields the experimentally observed long-range attraction. Here we demonstrate theoretically and experimentally a new pulse interaction mechanism mediated by the continuum noise floor that is a universal feature in multipulse passively mode-locked lasers. Long-range attraction is facilitated by the depletion of the gain by the pulses, leading to an inhomogeneous noise floor that biases the timing jitter of the pulses and produces an effective interpulse potential with stable pulse bunch configurations. The pulses attract by suppressing electromagnetic fluctuations, as do conductors in the Casimir effect of quantum electrodynamics. This enables manipulation and design of multipulse waveforms to ultimately make them useful for application of mode-locked lasers.

Bistability in a ring erbium-doped fiber laser due to ejected backward amplified spontaneous emission

We show and identify the role of the backward amplified spontaneous emission (ASE) in inducing bistability and hysteresis in a unidirectional ring erbium-doped fiber (edf) laser. It results from the interplay between the signal and the backward ASE in the gain medium that is ejected from the fiber loop by an isolator. A removal of the isolator eliminates the bistability. Another important factor is the strong wavelength dependence of the absorption and emission coefficients and their ratio.

Thermalization of one-dimensional photon gas and thermal lasers in erbium-doped fibers

We demonstrate thermalization and Bose-Einstein (BE) distribution of photons in standard erbium-doped fibers (edf) in a broad spectral range up to ~200nm at the 1550nm wavelength regime. Our measurements were done at a room temperature ~300K and 77K. It is a special demonstration of thermalization of photons in fiber cavities and even in open fibers. They are one-dimensional (1D), meters-long, with low finesse, high loss and small capture fraction of the spontaneous emission. Moreover, we find in the edf cavities coexistence of thermal-equilibrium (TE) and thermal lasing without an overall inversion (T-LWI). The experimental results are supported by a theoretical analysis based on the rate equations.

CW laser light condensation

We present a first experimental demonstration of classical CW laser condensation in the frequency (mode) domain. It also sheds light on the general question of photon-BEC (Bose-Einstein condensation) in laser cavities.

Casimir-Like Light Pulse Interaction Induced by Amplified Spontaneous Noise in Laser Cavities

We present a new mechanism for light pulse interaction in mode-locked lasers induced by amplified spontaneous noise. It is a time-light domain Casimir-like mechanism. We show experimental evidence for this unique effect.

Long Range Soliton Interaction Related to Sidebands Generation in Mode-Locked lasers

Soliton formation in passively mode-locked lasers is often accompanied with spectral sidebands. We find how the exact spectral shape of the sidebands affects the long range interaction between pulses in a fiber laser cavity.

Pulse-Quasi-Crystal Formation in Mode-Locked Lasers

Many-pulse formation in passively mode-locked fiber lasers is shown to exhibit self pulse crystallization phenomena. We present experimental demonstrations and theoretical thermodynamic-like modeling.

First experimental observation of critical phenomena in a mode-locked laser

We report on a first experimental observation of critical behavior in a laser system with passive mode-locking and external pulse injection. The critical exponents were found to match the theoretical values of beta = 0.5 and delta = 3 .