Co-MOFs as Emerging Pulse Modulators for Femtosecond Ultrafast Fiber Laser

Synergistic effects of europium doping on MOF-5: exploring its photoluminescent and non-linear optical behaviour for enhanced optical limiting

Metal-organic frameworks (MOFs) are researched widely for their linear optical properties, while their non-linear optical (NLO) properties are rarely investigated. This report discusses the behaviour of MOF-5 and its ability to bond with a europium moiety to exploit its NLO properties using the Z-scan technique. A partial deterioration in the Raman spectra and quenching of light in the PL spectra in some samples emphasised the need to study their ability to exhibit phosphorescence. TR-PL analysis revealed nanosecond lifetime values, which were attributed to their ability to fluoresce owing to the weak bonding between the 1,4-benzenedicarboxylic linker and europium ions. The same deterioration was found in the non-linear absorption studies for these samples. Enhanced structural and optical properties were found in the 1% doped sample (M_1) that exhibited a reverse saturable absorption (RSA) in the Z-scan technique, which led us to find its optical limiting threshold (1.53 × 1012 W m-2) and non-linear absorption co-efficient (β = 2.12 × 10-10 mW-1). An intensity-dependent non-linear absorption study revealed the presence of sequential two-photon absorption. These cumulative findings emphasize the potential of Eu3+-doped MOF-5 as a promising material for NLO applications, with the M_1 sample demonstrating the best optical performance amongst the pure and doped MOF-5 samples.

Tunable Multisoliton State Ultrafast Fiber Laser Based on NiSe and Generation of Vector Dual-Wavelength Solitons

As a member of the chalcogenide family, NiSe exhibits a direct bandgap of 1.74 eV, making it a promising candidate for nonlinear optical devices. However, its potential in the near-infrared region of the telecommunication band has not been fully explored. In this study, a well-coupled saturable absorber (SA) device is fabricated for the first time using NiSe nanosheets, and it is applied to an ultrafast fiber laser, achieving an ultrashort pulse laser output with an optical conversion efficiency of 13.9%. The laser based on NiSe SA achieves tunable multisoliton mode locking, including conventional solitons, bound-state solitons, dual-wavelength solitons, and second to fourth harmonic solitons, over a wavelength range of 1528.5-1556 nm by adjusting the resonator's polarization state through the polarization controller and controlling the pump power. Numerical simulations and soliton dynamic analysis in the study of NiSe SA reveal the intricate details and behaviors of ultrafast soliton pulse locking. The results indicate that the well-coupled NiSe SA, characterized by a modulation depth of 36.73%, a saturation intensity of 0.287 MW/cm2, and excellent spectral broadband absorption properties, can enhance intracavity nonlinear effects and enable the realization of stable and tunable multisoliton mode-locked pulses. Additionally, soliton collisions with group velocity differences are investigated under stable dual-wavelength soliton output, especially vector dual-wavelength soliton. This demonstrates the excellent application potential of NiSe SA in fields such as ultrafast optical communications and information encryption.

Application and Output Performance Comparison of Janus and Traditional Transition Metal Chalcogenides in Ytterbium-Doped Fiber Lasers

Janus transition metal disulfide (TMD) monolayers have two distinct carbon surfaces that break the inherent ground external mirror symmetry. When compared to traditional TMD materials, Janus TMDs not only inherit the advantages of traditional TMDs but also have new characteristics that are different from those of traditional TMDs. This paper describes the development of a stable passive Q-switched ytterbium-doped fiber laser (YDFL) with operating wavelengths of 1032.9 and 1030.6 nm using two saturated absorbing materials: tantalum sulfide (TaSSe) and tantalum disulfide (TaS2). Our experimental results show that TaSSe, as a saturable absorber (SA), can generate a higher single-pulse energy and withstand higher pump power, and the single maximum pulse energy can reach 108.81 nJ. In the TaS2-SA Q-switched YDFL, increasing pump power from 180 to 330 mW results in a minimum pulse width of 3.18 μs. The maximum pulse energy is 50.68 nJ. This study showed that Janus TMD TaSSe has superior optical properties compared to traditional TMD TaS2, indicating that it has great potential for use in fiber laser development.

Organic dye-loaded reduced titanium dioxide as a broadband saturable absorber for ultrafast fiber lasers

As a rising star among metal oxide nanomaterials, titanium dioxide (TiO2) has been widely investigated and employed in optical applications because of its excellent optical properties. In this work, we demonstrate the efficient and broadband nonlinear photonic properties of methylene blue (MB)-loaded reduced TiO2 (TiO2-x-MB) and explore the performance of a TiO2-x-MB-microfiber photonic device in broadband ultrafast photonics. Within an erbium-doped fiber laser (EDFL) system, utilizing the TiO2-x-MB-microfiber photonic device as a saturable absorber (SA), steady mode-locked pulses together with chaotic pulses were successfully achieved at the wavelength of 1.55 μm. Furthermore, by incorporating the TiO2-x-MB SA into a thulium-doped fiber laser (TDFL) system, an ultrashort single pulse and multiple pulses were obtained at 2.0 μm. These results indicate that TiO2-x-MB is an excellent nanomaterial for use in mode-locked lasers, being an alternative candidate for ultrafast fiber lasers via exploiting the chemical and physical properties of oxide nanomaterials.

Wave structure function, spatial coherence radius, and Fried parameter of optical wave propagating through ocean turbulence with a slant path

The analytical formula for characteristic parameters of optical wave (wave structure function, spatial coherence radius, and Fried parameter) in the slant path of ocean turbulence are derived and analyzed. Under the Rytov approximation, the wave structure function derived by the oceanic power spectrum of the refractive index of optical turbulent fluctuations in the slant path still complies with the five-thirds power law of the Kolmogorov spectrum in the inertial subregion, and the relationship between spatial coherence radius and Fried parameters satisfies 2.1 times. The correctness of analytical formulation of the wave structure function is demonstrated by comparing the numerical results of the original integral formula with the analytical formula of the derived in this paper.

High-velocity measurement method in dual-frequency laser interference tracker based on beam expander and acousto-optic modulator

The laser tracker, as a new large-scale measuring instrument of combining conventional measurement technology and modern control technology, has the advantages of intelligence, portability, large measurement space, high measurement accuracy and short detection period. However, the laser tracker has strict requirements on the moving speed of the spherically mounted retroreflector. This deficiency not only limits the application of the measuring instrument in the field of high-velocity measurement, but also greatly reduces the measurement efficiency. In this work, we analyze the factors that affect the tracking velocity of the laser tracker, and propose for the first time to use the beam expander device to improve the transverse tracking measurement velocity of the instrument. The experimental results show that the laser tracker miss distance can reach 2.25 mm. The transverse tracking velocity and acceleration can reach 4.34 m/s and 2.4 g, respectively. Additionally, the acousto-optic modulator is used to increase the frequency difference between the reference beam and the measuring beam, so that the value is greater than 19 MHz. The radial tracking measurement velocity can reach 6.2 m/s. The high-velocity laser interference tracker developed by this new method can be used in the field of large-scale space precision measurement such as nuclear power, medical treatment and rail transit.