arXiv subjects

Hossein Fathi

Publications and source records attributed to Hossein Fathi.

5 recordsLinked to original sources

arXiv2025

Power-Scalable Generation of High-Order Optical Vortices Via Coherent Beam Combining

Structured light beams, such as optical vortices carrying orbital angular momentum, are essential for applications ranging from low-power optical communications to high-intensity laser-matter interactions. However, scaling their power and energy while preserving complex phase and spatial structures remains a fundamental challenge. In this work, we demonstrate coherent beam combining as a versatile and scalable method for generating high-power structured beams without limitations on topological charge or spatial structure, while maintaining exceptionally high modal purity. We experimentally implement coherent beam combining for optical vortex beams with topological charges l = 1, 5, and 8, achieving a combined average power of 100 W and a peak power of 100 kW, with combining efficiencies of 95.0%, 93.9%, and 91.2%, respectively. Off-axis digital holography confirms that the phase and intensity profiles of the combined beams retain high modal purity, even at high topological charges. These results establish coherent beam combining as an effective route to high modal purity structured light at high power levels, unlocking new opportunities for advanced photonics and high-intensity light-matter interaction studies.

physics.optics↗

arXiv2025

High-purity amplification of circularly polarized orbital angular momentum modes in an active spun ring-core tapered fiber

Structured light, optical fields engineered in their spatial, polarization, or phase degrees of freedom, has become a key resource across advanced communication, sensing, imaging, and quantum technologies. Optical fibers nowadays play an essential role in this landscape, providing stable and scalable platforms for guiding, and amplifying complex modes such as vector and orbital angular momentum (OAM) beams. In this work, we demonstrate an active spun ring-shaped tapered fiber as a gain medium for efficient amplification of OAM modes preserving their modal purity and polarization topology. OAM beams with topological charges l = 1 and l = 2 carrying 60 ps pulses at 15 MHz repetition rate at 1030 nm wavelength are amplified over 1.2 W average power with modal purity over 95%. The spatially resolved measurement of the OAM beam polarization topology revealed small distortion due to the coupling in to neighbour modes. These results demonstrate the high potential of active spun ring-shaped tapered fibers for power scaling of complex beams, preserving their phase and polarization structure simultaneously.

physics.optics↗

arXiv2025

High-power monolithic narrow-linewidth 1.6 mJ/8 ns fiber laser system based on all-glass spun tapered double-clad fiber amplifier

High-energy, narrow-linewidth nanosecond pulses are highly demanding for many applications that require high temporal and spatial coherence. However, the amplification of narrow-linewidth pulses is primarily limited by stimulated Brillouin scattering, which causes pulse instabilities, back-reflected pulses, and catastrophic damage effects on optical components. In this work, we present a 1.6 mJ narrow-linewidth nanosecond pulsed fiber laser system based on all-glass spun tapered double-clad fibers without employing any mitigating technique for the stimulated Brillouin scattering effect. The system delivers pulses with an 8 ns duration at a 100 kHz repetition rate, over 97.5% degree of polarization, a beam quality factor of M2 = 1.3, a spectral linewidth of 53.8 MHz, a 160 W average power, and 188 kW peak power with a slope efficiency of 97.6%. The degree of spatial coherence of the amplified signal was measured to be 0.94. Our results are highly valued in applications requiring high-energy, high-coherence pulses with spectral, spatial, and polarization characteristics in a compact system.

physics.optics↗

arXiv2024

Versatile High-Power Monolithic All-Glass Fiber Amplifier for Pulsed Signals with a Wide Range of Repetition Rates

This study presents a compact, high-power monolithic all-glass spun tapered double-clad fiber amplifier for single-stage amplification of narrow linewidth picosecond pulsed signals from a few tens of mW to several hundred Watts of average power and MW level of peak power, covering a wide range of repetition rates. The absence of free-space elements in the amplifier module enhances its overall reliability by omitting the dependency on the pump alignment and internal back reflections. The versatile all-glass amplifier module delivers 50 ps pulses with over 2 MW peak power at 1 MHz, 50 ps pulses with over 625 W average power at 20 MHz, and 20 ps pulses with over 645 W average power at 1 GHz, all exhibiting excellent spectral, spatial, and polarization characteristics. This monolithic all-glass ultra-large mode area fiber amplifier is verified as a robust solution for direct amplification of short pulses attaining high peak/average power laser systems with excellent spectral, spatial, and polarization characteristics.

physics.optics↗

arXiv2023

Coherent beam combining of optical vortices

We experimentally demonstrate the power scaling of optical vortices by the coherent beam combining, encompassing topological charges ranging from l=1 to l=5 realized on the basis of a Yb-doped fiber short-pulsed laser system. The combining efficiency varies from 83.2 to 96.9% depending on the topological charge and beam pattern quality generated by the spatial light modulators. These results open a pathway to high-intensity optical vortices with enormous potential applications in science and industry by utilizing advances in light-matter interactions.

physics.optics↗