Search Results (70)

Mid-infrared (MIR) supercontinuum (SC) sources are critical for spectroscopy, biomedical imaging, and environmental monitoring. However, conventional generation methods based on free-space experiments using optical parametric amplifiers (OPAs) and difference frequency generation (DFG) lasers suffer from narrow bandwidth and low power distribution in the MIR region. This paper presents a cascaded pumping technique using two soft-glass fibers. A picosecond thulium-doped fiber amplifier (TDFA) pumps a Germania-doped fiber (GDF) to generate an intermediate broadband spectrum, which then pumps a fluorotellurite fiber (TBY) with higher nonlinearity and a wider transmission window. Using this configuration, we achieved an Octave-Spanning SC generation covering 1–4 μm with 7.20 W output power. Notably, 32.8% of total power lies above 3.0 μm, with 11.2% beyond 3.5 μm, demonstrating excellent long-wavelength performance. In addition, we applied numerical simulation methods to investigate SC generation in GDF and TBY by solving the nonlinear Schrödinger equation. The close match between simulated and experimental results facilitates theoretical examination of how SC broadening occurs. This cascaded approach offers a feasible solution in terms of spectral band matching, material compatibility, and system integration potential. Full article

A 50.9-W all-fiber mid-infrared (MIR) supercontinuum (SC) laser with a conversion efficiency of over 76.7% is demonstrated in a ZBLAN (ZrF₄–BaF₂–LaF₃–AlF₃–NaF) fiber. The entire system consists of a broadband thulium-doped fiber amplifier (TDFA) operating at 1.9–2.6 μm and a piece of ZBLAN fiber. The system features an all-fiber architecture, which is achieved by directly splicing the pigtail fiber of the TDFA to the ZBLAN fiber. The system’s stability and reliability were ensured by the utilization of the water-cooled fusion splicing joint between the silica fiber and ZBLAN fiber, and an AlF₃ fiber endcap. When the seed pulse repetition rate (PRR) was 3 MHz and the pulse duration was 6 ns, a MIR SC laser with an average power of 50.9 W and a spectral range of 1.9–3.6 μm was obtained, with a corresponding power conversion efficiency (from the TDFA output to the SC laser output) of 76.7%. By adjusting the pulse duration to 4 ns, the generated SC laser exhibited a spectral range of 1.9–3.7 μm and an average power of 50.1 W, corresponding to a power conversion efficiency of 75.1%. Such a supercontinuum (SC) laser paves the way for the application of high-power SC lasers in a wide range of fields. Full article

The temporal dynamics and statistical characteristics of Raman random fiber lasers are of great significance for studying their physical properties and applications. In this paper, the effect of pump dynamics on the temporal intensity statistical properties of Raman random fiber lasers is experimentally studied under full bandwidth measurements. The measured intensity probability density function (PDF) of the Raman random fiber laser pumped by an ytterbium-doped random fiber laser (YRFL) deviates inward from the exponential distribution. We further use the spectrally filtered YRFL with different temporal dynamics properties as the Raman pump, and the results reveal that the PDF of the Raman random fiber laser deviates outward from the exponential distribution, and the probability of extreme values increases by using a filtered YRFL pump with larger temporal intensity fluctuations. This work provides experimental evidence of the important role of pump properties on the statistics of a random Raman fiber laser, which could be crucial to tailoring the dynamics of random fiber lasers for various applications such as frequency doubling, supercontinuum generation, and laser inertial confinement fusion. Full article

We reported on a generation of 27 nm spectral bandwidth, two-port output ultrashort pulses directly from an all-normal-dispersion passively mode-locked Yb-fiber laser. Based on the nonlinear polarization rotation (NPR) mode-locking technique, high pump power and optical devices with high damage thresholds were introduced to achieve broad spectral bandwidth and strong output power. The dual wavelengths were emitted from the clockwise and counterclockwise ports, respectively, and self-started mode-locking was achieved. The bidirectional output laser generates stable pulses with up to 223.5 mW average power at a 46.04 MHz repetition rate, corresponding to a pulse energy of 5 nJ. The bidirectional ultrashort outputs of the laser provide potential applications in supercontinuum generation and medical and biological applications. Full article

This paper studies the coupling effect of laser intensity and waist radius on a series of electron radiation characteristics, such as radiation power, electron trajectory, a time spectrum, and a frequency spectrum. Through a large number of numerical simulations, based on the study of all radiation patterns, the influence laws and mechanisms of these two parameters are revealed. The larger the light intensity ${\mathit{a}}_{\mathbf{0}}$, the greater the influence of the waist radius ${\mathit{\omega }}_{\mathbf{0}}$ on the symmetry of the radiation power. When the light intensity is the same, the larger the waist radius, the greater the radiation power, the better the collimation, and the radiation power approximately satisfies a quadratic function. These results indicate that the radiation power can be rapidly increased by seven orders of magnitude through adjustment. Through a numerical simulation, we have obtained high-energy, high-frequency, high-collimation, good directivity, and supercontinuum X-rays. The above research has a pioneering guiding significance for the modulation of X-rays in optical laboratories. Full article

Under the framework of classical electrodynamics, this article investigates the nonlinear Thomson scattering generated by the cross-collision between a tightly focused linearly polarized Gaussian laser pulse and a relativistic electron through numerical simulation and emulation. The oscillation direction and emission angle of the electron’s trajectory are influenced by the beam waist radius and the delay time. The spatial radiation distribution of electrons exhibits a comet-shaped pattern, with the radiation being concentrated in the forward position. This is attributed to the high laser intensity at the focus, resulting in intense electron motion. As the beam waist radius keeps increasing continuously, the maximum radiation polar angle in the spatial distribution decreases. The time spectrum exhibits a symmetrical three-peak structure, with a high secondary peak. Meanwhile, the supercontinuum spectrum gradually transforms into a multi-peak distribution spectrum. In the multi-peak mode, the main peak and the secondary peak will interchange during the increase in the waist radius, generating rays with higher frequencies and energies. The aforementioned research findings reveal a portion of the mechanism of the nonlinear Thomson scattering theory and are beneficial for generating X-rays of higher quality. Full article

In this work, we experimentally investigate the characteristics of supercontinuum (SC) generation induced by femtosecond laser pulses with different polarization states in transparent medium. We employ a Mach–Zehnder Interferometer (MZI) to capture interference patterns during the filamentation process. The relative filamentation threshold, P_th, is measured for femtosecond laser pulses with different polarization states. The results demonstrate that the intensity of SC is strongly correlated with the polarization state of the incident laser pulses. At the same pulse energy, circularly polarized (CP) pulses suppress SC generation compared to linearly polarized (LP) pulses. Compared with weak external focusing, short-focal-length focusing significantly broadens the spectral range of SC. As the focal length of the focusing lens increases, the measured P_th values also increase. The P_th of the CP pulses is consistently higher than that of LP pulses. The experimental measurements of P_th for femtosecond lasers with different polarization states provide basic data support for the research on nonlinear characteristics. Full article

We demonstrate mid-infrared ultraflat broadband supercontinuum (SC) generation in a 40 cm long tapered fluorotellurite fiber pumped by a Raman soliton source. By tapering the end of the large-core-diameter fluorotellurite fiber, the dispersion is regulated and the nonlinear effect is enhanced, which effectively extends the mid-infrared SC spectral range and increases the spectral flatness. Finally, we obtained an SC light source with a spectral range from 1.8 to 4.7 μm; the 10 dB bandwidth of the source completely covers 1.88–4.22 μm, which has the farthest flat spectral edge in fluorotellurite fibers. The output power of the SC laser is about 1.04 W, and the power ratio of those above 3 μm in the spectrum to the total SC is ~24%. The optical-to-optical conversion efficiency is about 75%. Our results show that tapering of fluorotellurite fiber is an effective method to further extend and flatten the mid-infrared SC. Full article

Underground environments present a challenge for hyperspectral outcrop analysis. In addition to operational safety and moisture, illumination is the main concern in data acquisition. We report a supercontinuum laser for illuminating rock faces in hyperspectral data acquisition. We present the early results of combining an off-the-shelf hyperspectral camera with a supercontinuum laser system, measured at night on rock faces in a former open-pit mine in southeast Spain as a proxy for underground lighting conditions. Band ratios specifically developed for this geological setting and low-light conditions highlight key minerals that can be used as a vector toward the ore zone. We successfully highlight the key indicator minerals and their distribution patterns for defining gold-bearing ore zones and that supercontinuum white laser light is a feasible illumination source for hyperspectral line scanners under field conditions. Full article

We demonstrate a bidirectional fiber laser with an artificial saturable absorber of a step-index multimode fiber sandwiched by single-mode fibers. Two asynchronous noise-like pulse sequences with a repetition frequency difference of 3.16 kHz are obtained. The average power of the bidirectional asynchronous noise-like pulses is greater than 36 mW, and the pulse energy is greater than 3 nJ. The laser we demonstrate has potential applications in micromachining, supercontinuum spectrum generation, and signal processing. Full article

In the fields of agriculture and forestry, the Normalized Difference Vegetation Index (NDVI) is a critical indicator for assessing the physiological state of plants. Traditional imaging sensors can only collect two-dimensional vegetation distribution data, while dual-wavelength LiDAR technology offers the capability to capture vertical distribution information, which is essential for forest structure recovery and precision agriculture management. However, existing LiDAR systems face challenges in detecting echoes at two wavelengths, typically relying on multiple detectors or array sensors, leading to high costs, bulky systems, and slow detection rates. This study introduces a time-stretched method to separate two laser wavelengths in the time dimension, enabling a more cost-effective and efficient dual-spectral (600 nm and 800 nm) LiDAR system. Utilizing a supercontinuum laser and a single-pixel detector, the system incorporates specifically designed time-stretched transmission optics, enhancing the efficiency of NDVI data collection. We validated the ranging performance of the system, achieving an accuracy of approximately 3 mm by collecting data with a high sampling rate oscilloscope. Furthermore, by detecting branches, soil, and leaves in various health conditions, we evaluated the system’s performance. The dual-wavelength LiDAR can detect variations in NDVI due to differences in chlorophyll concentration and water content. Additionally, we used the radar equation to analyze the actual scene, clarifying the impact of the incidence angle on reflectance and NDVI. Scanning the Red Sumach, we obtained its NDVI distribution, demonstrating its physical characteristics. In conclusion, the proposed dual-wavelength LiDAR based on the time-stretched method has proven effective in agricultural and forestry applications, offering a new technological approach for future precision agriculture and forest management. Full article

Photoacoustics can provide a direct measurement of light absorption by microalgae depending on the photosynthesis pigment within them. In this study, we have performed photoacoustic flowmetry on living microalgae cells to measure their flow characteristics, which include flow speed, flow angle, flow direction, and, more importantly, the photoacoustic absorption spectrum, all by observing the photoacoustic Doppler power spectra during their flowing state. A supercontinuum pulsed laser with a high repetition frequency is used as the light source: through intensity modulation at a specified frequency, it can provide wavelength-selectable excitation of a photoacoustic signal centered around this frequency. Our approach can be useful to simultaneously measure the flow characteristics of microalgae and easily discriminate their different species with high accuracy in both static and dynamic states, thus facilitating the study of their cultivation and their role in our ecosystem. Full article

Previous studies of formation of extremely compressed wave packets during femtosecond filamentation in the region of anomalous group velocity dispersion in solid dielectrics mostly considered the case of linearly polarized laser pulses. However, recent results suggest potential applications of polarization state manipulation for ultrafast laser writing of optical structures in bulk solid-state media. In the present work, evolution of radiation polarization parameters during formation of such extreme wave packets at the pump wavelength of 1900 nm in fused silica is studied numerically on the basis of the carrier-resolved unidirectional pulse propagation equation (UPPE). It was revealed that initial close-to-circular polarization leads to higher intensity of the anti-Stokes wing in the spectrum of the generated supercontinuum. Numerical simulations indicate a complex, space–time variant polarization state, and the resulting spatiotemporal electric field distribution exhibits a strong dependence on the initial polarization of the femtosecond pulse. At the same time, electric field polarization tends to linear one in the region with the highest field strength regardless of the initial parameters. The origin of this behavior is attributed to the properties of the supercontinuum components generation during filament-induced plasma formation. Full article

We theoretically demonstrate a scheme to generate circularly polarized (CP) isolated attosecond pulses (IAPs) with tunable helicity using a polarization gating laser field interacting with the CO molecule. The results show that a broadband CP supercontinuum is produced from the oriented CO molecule, which supports the generation of an IAP with an ellipticity of 0.98 and a duration of 90 as. Furthermore, the helicity of the generated harmonics and IAP can be effectively controlled by modulating the laser field and the orientation angle of the CO molecule. Our method will advance research on chiral-specific dynamics and magnetic circular dichroism on the attosecond timescale. Full article

Supercontinuum (SC) generation pumped by fiber lasers with short wavelengths below 2.0 μm is important since it can provide a compact light source for various applications. We review the progress of SC generation in various materials regarding the formation of the waveguides and point out the existing issues in the current investigations and possible solutions in the future. Full article