M2 Factor Research Articles

STUDY MAGNETIC ELECTRON SCATTERING FORM FACTOR OF 24Mg ISOTOPE

The magnetic form factor of 24Mg isotope under inelastic electron scattering was subjected to computational scrutiny via the utilization of the Oxbash code. The endeavor involved elucidating energy levels intrinsic to this nucleus through the application of the shell model, wherein the model space encompassed zbm, psd, spsdpf, and sd configurations. In the context of the sd model, the investigation harnessed two pioneering USD-type Hamiltonians, denoted as USDC and USDI, in conjunction with tailored amendments to these interaction potentials, referred to as USDCm and USDIm. This study culminated in comprehensively juxtaposing all computational outputs with empirical data sources, including information extracted from the National Nuclear Data Center (NNDC) repository. Significantly, this systematic examination underscored a notable congruence between the derived computational outcomes and the empirical observations. This alignment became conspicuously pronounced subsequent to judicious adjustments made to the g-factors, specifying values of = 1.060 and = -0.060. The profound unity between the findings of this study and experimental data manifests as compelling evidence, substantiating the efficacy and precision of the employed interaction models. It implies a reliable capacity of these models in the precise computation of magnetic form factors M1, M2, and M3

Plasmonic-nanowire near-field beam analyzer

Abstract Experimental near-field analysis of the output beams from the end faces of micro/nano-waveguide is very necessary, because important information such as spatial intensity distributions, mode orders, and divergence angles can be obtained, and are very important for investigating and designing nanophotonic devices. However, as far as we know, it has not been demonstrated yet. In this work, we experimentally demonstrate a plasmonic-nanowire near-field beam analyzer, utilizing a single Au nanowire (AuNW) as the probe to scan the spatial near-field distributions of emitted beams from micro/nano-waveguide end-faces. Our analyzer can resolve the trade-off between high measurement resolution and light collection efficiency in conventional beam analyzers by a reverse nanofocusing process, achieving a probe resolution of 190 nm (<λ/8) and a simulated collection efficiency of ∼47.4 % at λ = 1596 nm. These attractive advantages allow us to obtain three‐dimensional (3D) scanning in a large range from the plasmonic hotspot region to the far-field region, characterizing the 3D spatial distribution evolution from a metal nanowire output beam for the first time, with an M 2 factor lower than that of the ideal Gaussian beam (M 2 = 1). In addition, the analyzer also demonstrates simultaneous characterization of multimodes in irregular and large-sized nanoribbons, further verifying its ability to selectively explore complex multimodes that are difficult to be predicted by numerical simulations. Our results suggest that this plasmonic-nanowire beam analyzer may hold promise for diverse near-field applications for micro/nano-waveguides such as nanolasers and biosensing, and offer a new method for understanding nanophotonic structures.

Distribution of intensity and M2 factor for a partially coherent flat-topped beam in bidirectional turbulent atmosphere and plasma connection

This study investigates the bidirectional transmission of a partially coherent flat-topped beam in a turbulent atmosphere and plasma. Analytical formulas for the intensity distribution and M2 factor are derived based on the optical transmission matrix, Collins formula, and second moment theory with Wigner distribution function. Numerical results show that the beam order and transverse spatial coherence width can be selected appropriately to mitigate turbulence and plasma induced evolution properties. The partially coherent flat-topped beam propagation through a turbulent atmosphere and plasma of the forward transmission effect on the intensity distribution and M2 factor are smaller than that of the reverse transmission. Under the same conditions, the M2 factor of a partially coherent flat-topped beam is smaller than the Gaussian beam in bidirectional transmission. Our results can be used in long-distance free-space optical communications.

Brightness enhancement on random-distributed-feedback Raman fiber lasers pumped by multimode diodes

Abstract The power scaling on short wavelength (SW) fiber lasers operating around 1 μm are in significant demand for applications in energy, environment and industry. The challenge for performance scalability of high-power SW lasers based on rare-earth-doped fiber primarily lies in the physical limitations, including reabsorption, amplified spontaneous emission and parasitic laser oscillation. Here, we demonstrate an all-fiberized, purely passive SW (1018 nm) random-distributed-feedback Raman fiber laser (RRFL) to validate the capability of achieving high-power output at SWs based on multimode laser diodes (LDs) direct pumping. Directly pumped by multimode LDs, the high-brightness RRFL delivers over 656 W, with an electro-optical efficiency of 20% relative to the power. The slope efficiency is 94%. The beam quality M2 factor is 2.9 (which is ~20 times that of the pump) at the maximum output signal power, achieving the highest brightness enhancement of 14.9 in RRFLs. To the best of our knowledge, this achievement also represents the highest power record of RRFLs utilizing multimode diodes for direct pumping. This work may not only provide a new insight into the realization of high-power, high-brightness RRFLs but also is a promising contender in the power scaling of SWs below 1 μm.

3.4 μm mid-infrared pulse train laser based on stepped acousto-optic <i>Q</i>-switched external cavity pumped MgO:PPLN optical parametric oscillator

3.4 μm mid-infrared pulse train laser generates the characteristic spectral lines of absorption peaks of CH<sub>4</sub>, NO<sub>2</sub> and other molecules. Its pulse train working mode can increase the signal-to-noise ratio of laser detection echo signal. It has broad application prospects in radar detection, environmental monitoring, spectral analysis and other fields, which has aroused great interest of scientists. Compared with the traditional intra-cavity control method, the step <i>Q</i>-switching method has the advantages of simple structure, high energy utilization rate and accurate control. Therefore, in this paper, both the theoretical study and the experimental study of a 3.4 μm mid-infrared pulse train laser pumped by a step-type acousto-optic <i>Q</i>-switched external cavity in MgO:PPLN optical parametric oscillator are carried out. The theoretical model of fundamental frequency step acousto-optic <i>Q</i>-switching is established. The change trends of photon number density at different step intervals are simulated. The optimal trigger time of step signal required for step acousto-optic <i>Q</i>-switching is obtained. The possibility of obtaining pulse train laser output by step acousto-optic <i>Q</i>-switching is determined. In the simulation, the single pulse envelope contains 3 sub-pulse train waveforms. The pulse width of the sub-pulse in the pulse envelope gradually increases, the sub-pulse interval is 5 μs, and the pulse envelope repetition frequency is 20 kHz. At the same time, the optimal trigger times for the step signal are obtained to be 16.00, 21.00, 26.00, 50.00 μs. The mid-infrared pulse train laser experiment of step acousto-optic <i>Q</i>-switched external cavity pumped MgO:PPLN optical parametric oscillator is carried out, and the 3.4 μm mid-infrared pulse train laser output containing three sub-pulses in a single pulse envelope is obtained. The sub-pulse interval is 5 μs, the narrowest pulse width is 12.8 ns, and the pulse envelope repetition frequency is 20 kHz, when the maximum average output power is 1.08 W, the maximum optical-to-optical conversion efficiency of 1064 nm fundamental light and 3.4 μm parametric light is 10.05%, and the beam quality factor <inline-formula><tex-math id="Z-20240205221930">\begin{document}$M^2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231348_Z-20240205221930.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231348_Z-20240205221930.png"/></alternatives></inline-formula> is 2.01. The output position of the sub pulses in each repetition period in the experiment is basically consistent with the simulation result, and it is found in both simulation and experiment that the width of the sub pulses within each pulse envelope gradually increases. The experimental results show that 3.4 μm mid-infrared pulse train laser output can be obtained by using step AOQS combined with OPO. This innovative method provides theoretical and technical support for detecting atmospheric pollutant concentration by using mid-infrared pulse train laser.

382 mW External-Cavity Frequency Doubling 461 nm Laser Based on Quasi-Phase Matching

To rapidly improve strontium optical clocks, a high-power, high-efficiency, and high-beam-quality 461 nm laser is required. In blue lasers based on periodically poled KTiOPO4 crystals, the optical absorption in the crystals can induce thermal effects, which must be considered in the design of high-efficiency external-cavity frequency doubling lasers. The interdependence between the absorption and the thermally induced quasi-phase mismatch was taken into account for the solution to the coupled wave equations. By incorporating multilayer crystal approximation, a theoretical model was developed to accurately determine the absorption of the frequency doubling laser. Based on experimental parameters, the temperature gradient in the crystal, the influence of the boundary temperature on the conversion efficiency, and the focal length of the thermal lens were simulated. Theoretical calculations were employed to optimize the parameters of the external-cavity frequency doubling experiment. In the experiment, in a bow-tie external cavity was demonstrated by pumping a 10 mm long periodically poled KTiOPO4 crystal with a 922 nm laser, a 461 nm laser with a maximum output power of 382 mW. The conversion efficiency of the incident fundamental laser was 66.2%. The M2 factor of the frequency doubling beam was approximately 1.4.

Watt-level LED-pumped actively Q-switched 1319 nm laser with high repetition rate operation

In this paper, we exhibited a watt-level acousto-optical (A-O) Q-switched 1319 nm laser based on a high-efficiency LED-pumped Nd:YAG laser module with high average power and high repetition rate operation. For the quasi-continuous wave (QCW) running operation, the average output power of fundamental laser at 1319 nm was as high as 4.73 W with a pulse length of 972 μs at a repetition rate of 100 Hz. After the resonator structure was optimized by A-O Q-switched modulation, the maximum power was 2.35 W at a repetition frequency of 5 kHz with a pulse width of 1.52 μs, and the M2 factor was measured to be about 9.4. To the best of my knowledge, this is the first demonstration, the maximum average power and high repetition rate watt-level output of an LED-pumped A-O Q-switched 1319 nm laser reported to date.

Solid-core anti-resonant fiber based on silicate glass

A silicate-glass-based solid-core anti-resonant fiber was fabricated by drilling and rod-in-tube method in this work. The fiber with a core diameter of 37.5 μm exhibited confinement loss of 1.33 dB/m at the anti-resonant wavelength of 1812.5 nm when subtracting the glass material loss. The laser at 1812.5 nm showed a beam quality with M2 factor of 1.56 after propagating in the anti-resonant fiber with a length of 0.3 m. Future improvement of raw material purity and optimization of fiber uniformity would promote the fiber transmission performance to extend its practical applications in high-power fiber laser and novel fiber device development.

Modulated high-order Hermite-Gaussian beams with uniform intensity distribution

Hermite-Gaussian beams have been studied since the early years of laser modes. With the recent development of structured light, different modulation methods have been demonstrated to control the energy, polarization and propagation behavior of Hermite-Gaussian beams. In this work we introduce an inverse design approach to modulate the energy distribution among different lobes of Hermite-Gaussian beams. In this approach, the desired intensity profiles of Hermite-Gaussian beams are the starting point. The required spatial phase masks are calculated through inverse Fourier transform, then projected on a spatial light modulator to convert conventional Gaussian beams into modulated Hermite-Gaussian beams. The experimental modulated high-order (m = 10, n = 10) Hermite-Gaussian beams show much improved energy distribution among different lobes over standard Hermite-Gaussian beams. These modulated Hermite-Gaussian beams also have improved beam quality factor M2 after modulation. These results demonstrated the feasibility to fine-tune the intensity profiles of Hermite-Gaussian beams, which have applications in structured illumination, particle manipulation and optical communications.

2 × 4.5 kW bidirectional output near-single-mode quasi-continuous wave monolithic fiber laser

Quasi-continuous wave (QCW) laser has a very broad application in the industrial field, especially in additive manufacturing, surface treatment, laser cutting, laser cleaning, and laser drilling. Compared with the unidirectional fiber laser, the bidirectional output can be achieved two ports high power output with only one resonator, which can greatly reduce the industrial cost. However, there are few researches on QCW fiber lasers with bidirectional output. Here, we optimized and demonstrated a bidirectional output QCW laser with output power of 2 × 4.5 kW based on a double-clad ytterbium-doped fiber with a core/cladding diameter of 25/400 μm. The peak power at both ends reached 4515 W and 4694 W, respectively. The Raman suppression ratio at both ends of A and B is about 12 dB, and the beam quality factor M2 is about 1.37 and 1.42, respectively. The corresponding optical-to-optical efficiency is 79%. To the best of our knowledge, this is the highest peak power of QCW laser with near-single-mode beam quality in a bidirectional structure laser.

10kW tandem pumping fiber amplifier with good beam quality based on tapered ytterbium-doped fiber.

In this paper, we established a high power tandem pumped fiber amplifier based on tapered ytterbium-doped fiber (TYDF). The TYDF is developed in-house with a core/inner cladding diameter of 30/250 µm at the small-core region and 48/400 µm at the large-core region. The key parameters of the amplifier in a co-pumped and counter-pumped configuration are experimentally investigated, such as slope efficiency, stimulated Raman scattering (SRS) threshold, and beam quality evolution. Up to 10.28 kW laser free of SRS or transverse mode instability is obtained from the counter-pumped amplifier, and the beam quality factor M2 is 2.29, which is significantly improved compared with the 48/400 µm uniform YDF. To the best of our knowledge, this is the highest average output power achieved so far based on the TYDF. This work could provide a solution for balancing the SRS suppression and high order modes control in high power tandem pumped YDF lasers.

3.38 kW all-fiberized narrow linewidth fiber laser based on active polarization control using RMS-Prop algorithm

Active polarization control in high power narrow linewidth non-polarization maintained (non-PM) fiber amplifier is investigated in this paper. The non-PM fiber laser is realized employing bidirectional pump configuration seeded with narrow linewidth laser source. Root-Mean-Square propagation (RMS-prop) algorithm is developed and first employed in polarization control technique. When control system does not work, the polarization extinction ratio (PER) of output signal laser varies between 0.25 dB and 4.61 dB. When control system works, the PER stably remains above 12.2 dB during power amplification. At laser power of 3.38 kW, the PER is 12.2 dB, 3 dB linewidth is measured to be ∼0.32 nm, and beam quality (M2 factor) is M2x = 1.39, M2y = 1.50. This is the first time to realize over 3 kW linearly polarized fiber laser based on active polarization control to the best of our knowledge.

Monolithic tapered Yb-doped fiber chirped pulse amplifier delivering 126 μJ and 207 MW femtosecond laser with near diffraction-limited beam quality

In this work, a high-energy and high peak power chirped pulse amplification system with near diffraction-limited beam quality based on tapered confined-doped fiber (TCF) is experimentally demonstrated. The TCF has a core numerical aperture of 0.07 with core/cladding diameter of 35/250 µm at the thin end and 56/400 μm at the thick end. With a backward-pumping configuration, a maximum single pulse energy of 177.9 μJ at a repetition rate of 504 kHz is realized, corresponding to an average power of 89.7 W. Through partially compensating for the accumulated nonlinear phase during the amplification process via adjusting the high order dispersion of the stretching chirped fiber Bragg grating, the duration of the amplified pulse is compressed to 401 fs with a pulse energy of 126.3 μJ and a peak power of 207 MW, which to the best of our knowledge represents the highest peak power ever reported from a monolithic ultrafast fiber laser. At the highest energy, the polarization extinction ratio and the M2 factor were respectively measured to be ~ 19 dB and 1.20. In addition, the corresponding intensity noise properties as well as the short- and long-term stability were also examined, verifying a stable operation of the system. It is believed that the demonstrated laser source could find important applications in, for example, advanced manufacturing and photomedicine.Graphical

4.55 W continue-wave dual-end pumping of Er:Yb:YAl3(BO3)4 microchip laser at 1.5 μ m

This paper demonstrates an eye-safe 1.5 μm continue wave (CW) Er:Yb:YAl3(BO3)4 (Er:Yb:YAB) microchip laser with dual-end pumping. By using a 1.5 mm thick Er:Yb:YAB crystal and 2.5% output coupling transmittance, its maximum output power could reach 4.55 W at the incident power of 15.4 W. This is the largest CW laser output power in the reported Er:Yb:YAB laser. The output laser beam was observed. The beam quality factors M2 in the X and Y directions were 1.65 and 1.71, respectively. The beam quality of the output laser of the CW Er:Yb:YAB microchip laser pumped by dual-end is significantly improved compared to previous works.

67 mJ, 137 ns narrow bandwidth 355 nm UV laser.

A high-efficiency, high-energy, narrow bandwidth, hundred-nanosecond pulse width 355 nm ultraviolet (UV) laser was realized. A high-energy single-frequency 1064 nm fundamental laser was demonstrated firstly with multistage end-pumped preamplifiers and side-pumped main amplifiers. The corresponding pulse energy, repetition rate, pulse duration, bandwidth, and beam quality factor M2 were determined to be 221 mJ, 100 Hz, 156 ns, 2.25 MHz, and 1.23, respectively. By using type-I phase-matching LBO crystal for second harmonic generation (SHG) and type-II phase-matching LBO crystal for the sum frequency generation of the third harmonic, 67 mJ, a narrow bandwidth 355 nm UV laser was obtained with a pulse width of 137 ns and an energy stability of RMS < 1.2%@2 h. The fundamental to UV optical conversion efficiency was 30.3%. Our results provided a new way for generating high-energy, narrow bandwidth hundred-nanosecond 355 nm UV lasers used for direct-detection Doppler wind lidar (DWL) system.

Beam quality control technology for solid-state lasers based on thermal effects.

Thermal effects under high-power pumping significantly limit the laser beam quality. To address this, we developed an M2 simulation algorithm based on ray trajectory simulation and established a corresponding experimental platform. This approach optimized the M2 factor of pulsed lasers to 2.2 and output power of 25.9 W under a repetition rate of 10 kHz. The results revealed that under specific conditions, thermal effects, typically considered detrimental to beam quality, could significantly enhance it. Compared to other methods necessitating additional optical components, our strategy offers a streamlined and straightforward solution for beam quality control under high-power pumping conditions.

Acousto-Optic Q-Switched Ho:YLF Ring Laser Based on Anti-Misalignment Resonant Cavity

An acousto-optic Q-switching Ho:YLF ring oscillator at 2066.33 nm with two anti-misalignment corner cube reflectors (CCRs) pumped by a 1940 nm thulium-doped fiber laser is demonstrated. The depolarization effect of the CCR is expressed in the form of equivalent transmission, and the transmission from two output directions of the oscillator is changing synchronously and periodically as the waveplate angle changes. In the experiment, under the pump power of 21.76 W, the optimum bidirectional energy of 3.13 mJ for a pulse duration of 122 ns at a repetition rate of 50 Hz is realized. The pulse energy reduction percentage at 50 Hz is 8% by changing the horizontal drift angle of one of the CCRs to 4.5°. The beam quality factor M2 is calculated to be about 1.10, revealing that the Ho laser is working in a fundamental transverse mode.

High-Power, High-Purity HG0n Hermite–Gaussian Laser Beam Generation in Cascaded Large Aspect Ratio Slabs

High-power, high-purity, nanosecond (ns) one-dimensional HG0n laser beams are proposed and demonstrated by using Nd:YAG cascaded slabs with a large aspect ratio. The HG0n laser beams are generated by adjusting the pump distribution, the intracavity apertures, and the tilt angle of the output coupler (OC). By controlling the gain and loss of HG0n modes of different orders, the high-purity, one-dimensional, high-order HG0n laser beams with orders 1 to 9 (HG01 to HG09) are produced, and their beam quality factors M2 align well with the theoretical predictions. Meanwhile, the large aspect ratio slab provides an ideal amplifier for the strip-shaped HG0n laser beams, and further power scaling is achieved by seeding the generated HG0n laser beams into an amplifier with an identical slab module. For the HG09 mode, the average power is amplified from 289 mW to 4.73 W with 294 ns pulse width, corresponding to a peak power of 32 kW. Moreover, above 5 W average power is achieved for all HG01 to HG08 modes. Hopefully, this scheme provides a solution for high-power and high-purity HG0n laser beam generation based on the slab-shaped configuration.

Design of Single-Mode Single-Polarization Large-Mode-Area Multicore Fibers.

In laser science and industry, considerable effort is directed toward designing fibers for fiber laser and fiber amplifier applications, each of which offers a particular advantage over the others. Evanescently coupled multicore fibers, however, have been studied less extensively due to the relatively small mode area in the single-mode regime. Here, by proposing a new structure with stress-applying parts in a 37-core fiber and optimizing this structure through a comprehensive framework, we present 21 solutions characterized by large-mode-area and high beam quality in the single-mode, single-polarization regime. Different fiber designs are optimal for different output parameters. In one design, the mode area can significantly increase to above 880 μm2, which is comparable with that of photonic-crystal fibers. Moreover, besides the single-mode operation, the beam quality factor (M2 factor) of the fundamental mode is considered an output parameter in the bent state and is improved up to 1.05 in another design. A comprehensive tolerance analysis is then performed to assess the performance of the designs under deviations from normal conditions. Moreover, in spite of the shifts in the loss of modes, the proposed high beam quality LMA fibers maintain single-polarization, single-mode operation across a wide range of core pitches, bending orientation angles, and bending radius deviations. Our results highlight the potential of multicore fibers for the efficient operation of fiber lasers and amplifiers.

Widely tunable near-infrared optical parametric oscillator based on a 5%MgO:PPLN partial cylinder pumped at 1064 nm by a 1-kHz sub-nanosecond microchip laser.

We report the implementation of a singly resonant optical parametric oscillator using a 5%MgO:PPLN partial cylinder pumped by a sub-nanosecond microchip laser emitting 1064 nm at a repetition rate of 1 kHz. It is continuously tunable from 1410 nm up to 4330 nm by rotating the cylinder and a total energy of several microjoules is emitted with a beam quality factor M2 lower than 3.