arXiv subjects

Alexander Bekker

Publications and source records attributed to Alexander Bekker.

4 recordsLinked to original sources

arXiv2022

Mysterious frequency combs in erbium-doped fiber lasers at low temperatures

We report on the observation of puzzling nonuniform, but ordered, frequency combs in erbium-doped fiber lasers at low temperatures, between 3 K and 14 K. At ~14 K the combs disappear. The combs contain ~240 lines and have nonuniform frequency spacings that starts from ~25 GHz at ~1540.5 nm and decreases, almost monotonically, to ~100 MHz within (1.8-2) nm. We discuss possibilities that they result from enlarged regular mode-comb spacings, from prime numbers-based solitary waves free of four-wave mixing or result from gain gratings. However, we think that the combs originate from multi-lasing lines allowed in inhomogeneous gain broadening, dominant at low temperatures, together with a small power dependent homogeneous broadening part, responsible for the spacing between the lines.

physics.optics↗

arXiv2017

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 lasing without an overall inversion. The experimental results are supported by a theoretical analysis based on the rate equations.

physics.optics↗

arXiv2011

Spectral Sidebands and Multi-Pulse Formation in Passively Mode Locked Lasers

Pulse formation in passively mode locked lasers is often accompanied with dispersive waves that form of spectral sidebands due to spatial inhomogoneities in the laser cavity. Here we present an explicit calculation of the amplitude, frequency, and precise shape of the sidebands accompanying a soliton-like pulse. We then extend the study to the global steady state of mode locked laser with a variable number of pulses, and present experimental results in a mode locked fiber laser that confirm the theory. The strong correlation between the temporal width of the sidebands and the measured spacing between the pulses in multipulse operation suggests that the sidebands have an important role in the inter-pulse interaction.

physics.optics↗

arXiv2004

Formation and annihilation of laser light pulse quanta in thermodynamic-like pathway

We present a theoretical and experimental study of multiple pulse formation in passively mode-locked (PML) lasers. Following a statistical mechanics approach, the study yields a thermodynamic-like "phase diagram" with boundaries representing cascaded first order phase transitions. They correspond to abrupt creation or annihilation of pulses and a quantized RF power behavior, as system parameters (noise and/or pumping levels) are varied, in excellent accordance with the experiments. Remarkably, individual pulses carry an almost constant quantum of energy.

cond-mat.stat-mech↗