Saturation Intensity Research Articles

Embedded gold nanoparticles in TiO2 crystal for photonic applications

• Plasmonic Au nanoparticles are synthesized in TiO 2 crystal by ion implantation. • Third-order optical nonlinearity tailoring is achieved through charge transfer between Au nanoparticles and TiO 2 . • Enhanced modulation depth and optimized saturation intensity suggest significant potential photonic applications. Gold nanoparticles (Au NPs) are synthesized inside TiO 2 crystal by Au + ion implantation. The incorporation of Au + ions in TiO 2 brings out the modification of optical features of the bulk due to the localized surface plasmon resonance (LSPR) effect. The linear absorption spectra of Au NPs dispersed in TiO 2 crystal possesses an absorption peak at 638 nm. The third order optical nonlinearities of TiO 2 with Au NPs are modulated with reduced saturation intensity and increased modulation depth, compared with pure TiO 2 bulk. Our results pave a way to use TiO 2 with embedded Au NPs for nonlinear photonic applications.

Can SIF and NPQ be used in the photosynthesis rate simulation of plants subjected to drought?

Solar-induced chlorophyll fluorescence (SIF) is a rapidly developed remote sensing technology and has been used to estimate leaf-level net CO 2 assimilation by a mechanistic light reaction (MLR-SIF) equation. However, the application of this model would be limited by the challenging measurement and estimation of input parameters (e.g., fraction of open PSII reaction centres, q L ). We modified the MLR-SIF model by replacing q L by the easily obtained parameters (non-photochemical quenching [NPQ]) to facilitate its application. We employed synchronous measurements of gas exchanges, ChlF parameters and SIF for Leymus chinensis , Populus tomentosa Carrières and Ulmus pumila var. sabulosa under the soil–water deficit and rehydration process to test the robustness of the modified MLR-SIF model. Our results demonstrated that for L. chinensis the net photosynthesis rate dynamics under severe drought stress and saturated water condition were effectively captured by the modified MLR-SIF model ( R 2 = 0.75–0.92, RMSE = 1.11–3.56) . For P. tomentosa Carrières and U. pumila var. sabulosa , the net photosynthesis rates were predicted by the modified MLR-SIF model with good accuracy ( R 2 = 0.86, RMSE = 9.44; R 2 = 0.88, RMSE = 4.16) across the water deficit and rehydration condition . However, the electron transport rate estimated by the modified MLR-SIF model uncoupled with the photosynthetic capacity ( r 2 = −0.13) and lowered the net photosynthesis rate simulation precision ( R 2 = 0.35, RMSE = 3.41) for L. chinensis under mild drought stress and saturated light intensities. The electron transport rate estimated by the modified MLR-SIF model downregulated the photosynthetic capacity for P. tomentosa Carrières ( r 2 = 0.32) and U. pumila var. sabulosa ( r 2 = 0.22) under mild drought stress. The shift of the Rubisco and RUBP limited state cross-points, the dynamic photosynthesis parameters across the plant species and the alternative electron sinks under soil–water deficit and rehydration process influenced the simulation precision of the modified MLR-SIF model. Our modified MLR-SIF model provided a basis for understanding and inferring the photosynthetic rate by SIF and NPQ under drought stress. • A mechanical link of SIF and NPQ to photosynthetic capacity was developed. • Carboxylation limitation state and photosynthesis parameters influence modified MLR-SIF simulation precision under drought and rehydration. • The electron transport rate estimated by SIF and NPQ uncoupled with the photosynthetic capacity under mild drought stress.

A Raman quantum free-electron laser model

Operation of a Quantum Free Electron Laser (QFEL) could provide a compact and fully coherent source of X- and γ-rays. Imperative to experimental realization is allowing for decoherence effects of either spontaneous emission or space-charge to take place, having opposing constraints. Here, for the first time, we present a one-dimensional QFEL Wigner model that includes longitudinal space-charge effects by quantizing the periodic potential derived from the Fourier components of the longitudinal electron beam density. The model is used to investigate steady-state QFEL gain and momentum state dynamics for a variety of space-charge regimes. We find increased saturation lengths and lower saturation intensity as a result of attenuated transitions in the two-level quantum system. In addition, we characterize a space-charge regime where specific transitions outside the QFEL bandwidth are targeted, such that the conventional description breaks down. These findings serve as a consistent theoretical extension of existing QFEL models.

Design of remote sensing-based geographic information system

To deal with problems of traditional geographic information collection, such as low real-time, poor authenticity of the data, and unclear description of detailed areas, a design scheme of remote sensing-based geographic information system is proposed. The system mainly consists of information collection, imaging processing, data storage management, scene control and data transmission module. By use of remote sensing technology, the reflected and radiated electromagnetic waves of the target area are collected from a long distance to form an image, and the hue–intensity–saturation (HIS) transformation method is used to enhance the image definition. Weighted fusion algorithm is adopted to process the details of the image. The spatial database stores and manages the text and image data respectively, and establishes the attribute self-correlation mechanism to render the ground objects in the picture with SketchUp software. Finally, using RS422 protocol to transmit information can achieve the effect of multi-purpose, and enhance the anti-interference of the system. The experimental results show that the practical experience of the proposed system is excellent, the geographic information image presented is clear, and the edge details are clearly visible, which can provide users with effective geographic information data.

2D self-assembled perovskite nanosheets as a nonlinear saturable absorber for passive Q-switched laser

Saturable absorbers (SAs) are essential devices for laser generation through passive Q-switch or mode-locking methods. Quantum-confined nanocrystals as excellent SAs have been attracted much attention. Self-assembled CsPbBr3 nanoplatelets (NPLs) were prepared at room temperature, which indicated nonlinear optical transmission with the modulation depth and the saturable intensity of 13.88% and 1.75 MW cm−2, respectively. The maximum repetition rate of CsPbBr3 NPLs is 1466 kHz, while corresponding pulse width is 69 ns. The nonlinear optical performance of CsPbBr3 NPLs indicate its potential applications in optical communication, laser pulses and nonlinear optics.

Tunable S-band mode-locked thulium-doped fluoride fiber laser using nickel phosphorus trisulfide (NiPS3) saturable absorber

Nickel Phosphate Trisulfide (NiPS3) prepared using the LPE technique was used as a saturable absorber (SA) in a thulium-doped fluoride fiber laser for the generation of mode-locked pulses. The polishing method was used to prepare the arc-shaped fiber before the NiPS3 solution was drop-casted onto it to form the SA device. The SA exhibited nonlinear optical properties, with modulation depth and saturation intensity of 29.44 % and 0.547 kW/cm2 respectively. Insertion of the SA in the TDFF cavity produced mode-locked pulses with central wavelength and 3-dB bandwidth of 1505 nm and 0.68 nm respectively, with a pulse width of 3.56 ps. The mode-locking operation also has a repetition rate of 582 kHz and an SNR of about 58 dB at a pump power of 280 mW. The maximum average output power measured was 2.4 mW at maximum pump power, with maximum pulse energy and peak power at 4.12 nJ and 1.16 kW respectively. Due to the optical interaction between NiPS3 and the evanescent wave in this arrangement, a larger damage threshold can be achieved, enabling the laser performance to operate at higher output power. Tunability was achieved by simultaneous adjustment of extinction and wavelength knob on the tunable Mach-Zehnder Filter (TMZF). The shape of spectra remained unchanged and continued exhibiting Kelly’s sidebands throughout the tunability range of about 2 nm. These results provide the first demonstration of tunable mode-locked pulses in the S-band region.

Graphene saturable absorber mirror for passive mode-locking of mid-infrared QCLs

Passive mode-locking in quantum cascade lasers (QCLs) remains one of the huge challenges because of the fast relaxation time of the excited carriers which is typically in the range of sub-picoseconds. The use of conventional techniques such as the semiconductor saturable absorber mirror is inefficient because the spatial hole burning effect dominates the carrier dynamics. To overcome this effect, longitudinal transition structures with relaxation time around $$50~\mathrm {ps}$$ were proposed. However, mode-locking is assured with an external modulation at a cavity roundtrip frequency. In this paper, we demonstrate that a single-layer graphene used as a saturable absorber permits to generate stable pulses in such structures. The graphene is integrated with a highly reflective mirror to increase the internal electric field and achieve the saturation intensity. The dynamic of the QCL is modeled with Maxwell-Bloch equations while Maxwell-Ampere equation is used for the graphene layer by considering a nonlinear conductivity. This system of equations is solved using the one-dimensional Finite-Difference Time-Domain ( FDTD) method. To model the single-layer graphene of a $$0.33~\mathrm {nm}$$ thickness, a specific sub-cell is implemented based on Maloney method. Simulation results of a $${\mkern 1mu} 6.2~\mu {\text{m}}$$ QCL with a diagonal radiative transition show a generation of isolated pulses with a peak electric field of $$80~\mathrm {MV.m^{-1}}$$ and a duration of $$51~\mathrm {fs}$$ . The mode-locking remains stable for QCLs with a vertical transition having a relaxation time below $$5~\mathrm {ps}$$ .

Structure of Fish Community in The Alas River of Aceh Tenggara District

Research on the Community Structure of Fish on the Alas River in Babul Makmur sub-district Aceh Tenggara district was conducted from April to October 2018. The aim of this research was to analyze the structure of fish communities and to analyze physical-chemical factors related to fish community structures in the water of the Alas River in Babul Makmur sub-district Aceh Tenggara district. This research using "Purposive Sampling" method on the location based on human activities i.e the tributary of the Lawe Pakam (household waste disposal), the meeting of 2 rivers (sand dredging), the river parent (tourism), the mountain stream (free of activity). Sampling using nets. Seven species of fish obtained from the study sites were classified into 3 ordo (Cypriniformes, Perciformes, Siluriformes). The result showed that station 1 had the highest fish density at 0.3 ind / m2 for species Tor tambroides. Station 3 had the highest fish diversity index at 1.6213. Temperature, phosphate, light intensity, light penetration, dissolved oxygen and oxygen saturation had strongly correlated with fish diversity in the waters of the Alas River.

Π‐Electron‐Extended Porphyrin‐Linked Covalent Organic Framework for a Q‐Switched All‐Solid‐State Laser

Herein, a new π‐electron‐delocalized building block (ProPh‐4CHO) is reported for the construction of a π‐electron‐extended porphyrin/pyrene‐linked covalent organic framework (ProPh‐PyTA‐COF) for use as a saturable absorber (SA) in a Q‐switched all‐solid‐state laser. Employing a mode‐locked fiber laser operated with 130‐fs pulses at 1030 nm and a repetition rate of 28 MHz, ProPh‐PyTA‐COF exhibits remarkable optical nonlinear absorptions: two saturable absorptions with saturation intensities of 92 MW cm−2 and 1 kW cm−2. This material is used to fabricate the first pulsed Q‐switched all‐solid‐state laser incorporating a COF as an absorber. The laser incorporating this COF‐SA exhibited a pump power of 6.5 W with a pulse duration of 1.2 μs, corresponding to a pulse repetition rate of 94.4 kHz. This study not only reveals the possibility of using saturation absorption to pulse a solid‐state laser but also opens up a new path toward optical nonlinearity through the engineering of π‐bond delocalization.

High-energy Q switched Yb-doped fiber laser based on a ternary layered structured Ti2AlC saturable absorber.

Ti2AlC is a kind of ternary layered structured ceramic metal compound, combining the advantages of both ceramic and metal. Herein, the saturable absorption performance of Ti2AlC at the 1-µm wave band is investigated. The Ti2AlC behaves with excellent saturable absorption, which has a modulation depth of 14.53% and a saturable intensity of 13.27 MW/cm2. An all-normal dispersion fiber laser based on the Ti2AlC saturable absorber (SA) is constructed. The repetition frequency of the Q switched pulses increased from 44 to 49 kHz as the pump power rose from 276 to 365 mW, and the corresponding pulse width decreased from 3.64 to 2.42 µs. The maximum output single Q switched pulse energy is as high as 169.8 nJ. Our experiments prove that the MAX phase Ti2AlC has potential as a low-cost, simple preparation, and broadband SA material. To the best of our knowledge, this is the first demonstration of Ti2AlC serving as a SA material achieving Q switched operation at the 1-µm wave band.

Dual wavelength generation and wavelength tunability in Yb-doped mode-locked laser using few-mode fiber as a saturable absorber

In this research, we demonstrate wavelength tunability and dual wavelength generation in all-fiber ytterbium (Yb)-doped mode-locked laser using a single mode–few-mode–single mode fiber (SMF–FMF–SMF) combination act as a saturable absorber (SA). The all-fiber SA exhibits high modulation depth of 34.53% and a saturation intensity of 9.17 MW/cm2. The SMF–FMF–SMF structure encompasses an inherent filtering along with SA property. By combining the tunable intra-cavity birefringence of the laser with the SA features result in dual-wavelength generation and wavelength tunability. Thus, the tuning of center wavelength of output spectrum from 1028.88 through 1076.18 nm, with the compressed pulse widths from 319 to 324 fs respectively, is achieved. Besides, the generated dual-wavelength is switched from 1033.32/1058.2 nm to 1049.7/1075.7 nm, respectively. These results indicate that an all-fiber SMF–FMF–SMF structure is a potential SA element for wavelength tunability and dual-wavelength mode-locking in Yb-doped fiber lasers, which can be used for nonlinear microscopy, bio-degradable material processing and terahertz spectroscopy.

High-responsivity operation of quantum cascade detectors at 9 µm.

Quantum cascade detectors (QCDs) are devices operating at zero external bias with a low dark-current. They show linear detection and high saturation intensities, making them suitable candidates for heterodyne detection in long-wave infrared (LWIR) free space optical communication systems. We present an approach to mitigate the performance limitation at long wavelengths, by a comparison of similar single and multi-period QCDs for optimizing their responsivity and noise behaviour. Our InGaAs/InAlAs/InP ridge QCDs are designed for operation at λ = 9.124 µm. Optical waveguide simulations support the accurate optical characterization. A detailed device analysis reveals room-temperature responsivities of 111 mA/W for the 15-period and 411 mA/W for the single-period device.

Large energy mode-locked phenomenon based on ZrS2 in Er-doped fiber laser

With high nonlinear effect and low band gap value, ZrS2 is a promising material in photovoltaic application. In our work, a ZrS2-polyvinyl alcohol thin film modulator was successfully prepared by liquid phase exfoliation. The modulation depth of ZrS2 saturable absorber is 6.3 % and its saturation intensity is 3.92 MW/cm2. Large energy mode-locked phenomenon was obtained in the Er-doped fiber laser with ZrS2 as an optical modulator. When the pump power was 1250 mW, the center wavelength, pulse repetition rate, and maximum pulse energy of the large energy mode-locked were 1531 nm, 604.23 kHz, and 23.65 nJ, respectively. This experiment proves that ZrS2 has excellent nonlinear absorption performance, also provides a reference for the future research of large energy mode-locked based on transition metal dihalogenateds.

Optical nonlinearity of Cu1.81S nanodisks decorated with silver nanoparticles

The nonlinear absorption (NLA) and ultrafast dynamics process of Cu1.81S nanodisks (NDs) and Ag-Cu1.81S nanocomposites are investigated by using femtosecond Z-scan measurements and femtosecond time-resolved transient absorption spectrum, respectively. After decoration with Ag particles, Ag-Cu1.81S nanocomposites exhibit stronger saturable absorption and smaller saturable intensity at 600 and 800 nm. The carrier relaxation time is measured using femtosecond time-resolved techniques, and the results showed that the prolongation of the carrier relaxation time of the composite material can lead to a stronger saturation absorption effect.

Application of Multimedia Semantic Extraction Method in Fast Image Enhancement Control

In order to solve the problem that it is difficult to effectively enhance the details of the compressed domain and maintain the overall brightness and clarity of the image when improving the image contrast in the current image enhancement method in the compressed domain, a multimedia semantic extraction method is applied in fast image enhancement control. It has been proposed that thealgorithm that synthesizes training samples according to the Retinex model converts the original low-light image from RGB (red-green-blue) space to HSI (hue saturation intensity) color space, keeps the chrominance and saturation components unchanged, and uses DCNN to enhance the luminance component; finally, it converts the HSI color space to RGB space to get the final enhanced image. The experimental results show that the performance of the model will increase with the increase of the number of convolution kernels, but the increase of the number of convolution kernels will undoubtedly increase the amount of calculation; it can also be found that when the number of network layers is 7, the PSNR of the image output by the model increases. The highest value, increasing the number of network layers, does not necessarily improve the performance of the model; with or without BN, his training method converges more easily than direct RGB image enhancement, with higher average PSNR and SSIM values. The experimental results show that, compared with the traditional Retinex enhancement algorithm and the DCT compression domain enhancement algorithm, the algorithm has better detail enhancement and color preservation effects and can better suppress the block effect.

Q-switched and mode-locked fiber laser based on organic metal 8-hydroxyquinoline chelate as saturable absorber at 1.5 µm

This paper reports the demonstration of bis(8-hydroxyquinoline) calcium (CaQ2) as a passive saturable absorber (SA) in an erbium-doped fiber laser cavity. The SA has a saturation intensity of 511 MW/cm2 and a modulation depth of 14%. As the SA was incorporated into the cavity, a Q-switching was produced with a repetition rate and pulse duration ranging between 45.5 and 88.2 kHz and 8.76 to 2.9 µs, respectively. Then by increasing the cavity length, a soliton mode-locking operation was developed with a repetition rate and pulse duration of 1.82 MHz and 1.6 ps, respectively. Both lasers had a signal-to-noise ratio (SNR) higher than 63 dB and a central wavelength of 1561 nm. Our results suggest that CaQ2 has the potentials to act as a stable and good-performance SA. We believe that this work is the first to report CaQ2 as a functioning and promising SA.

Defect assisted enhanced nonlinear optical performance and optical limiting of pure and doped BiVO4 powders and nanocomposite films

The linear and nonlinear absorption properties, photoluminescence and optical limiting properties of bismuth vanadate (BiVO4) powders and films were presented in this work. The structural, morphological and optical effects of different doping elements (M: Mo,W and Ni) were investigated (M: BiVO4). XRD and Raman results proved that BiVO4 and M: BiVO4 powders were synthesized in the monoclinic scheelite structure. Twhe powder morphology as found to be changed by Ni and W doping. The nonlinear optical responses of pure and M: BiVO4 were studied using the open aperture Z-scan experiment and a theoretical model was used to determine the nonlinear optical absorption performance. The nonlinear absorption coefficient (βeff) values were found to be 6.59 × 104, 8.86 × 104, 2.26 × 105 and 1.62 × 106 cm/GW for BiVO4, Mo: BiVO4, W: BiVO4 and Ni: BiVO4 nanocomposite films, respectively. The highest nonlinear absorption coefficients (βeff) and saturation intensity thresholds (ISAT) were obtained for Ni:BiVO4 film. Experimental results showed that the βeff value and band gap can be controlled by the dopant element, making doped BiVO4 a good candidate for nonlinear optical applications such as optical limiters, optical switches and modulators in integrated photonic devices.

LD pumped passively Q-switched Pr:YLF lasers using VS2 SA

Recently, two-dimensional vanadium disulfide (VS2) materials, as typical TMDs, have been successfully prepared and applied to lasers. Here, multilayer VS2 films were used as a saturable absorber (SA) in an all-solid-state visible laser. The VS2 films have a modulation depth of 34.1% and a saturation intensity of 27.5 µJ/cm2. Three wavelength passively Q-switched lasers were located at 522.7 nm, 639.4 nm, and 720.9 nm, respectively. The shortest pulse width for the three Q-switched lasers were 120 ns, 93 ns, and 108 ns. The experimental results indicate that VS2 is a promising SA material in an all-solid-state visible laser.

SiO2 passivated TaS2 saturable absorber mirrors for the ultrafast pulse generation

Since its inception as the cornerstone of the ultrafast pulse laser, semiconductor saturable absorber mirrors (SESAMs) have attracted considerable interest. Meanwhile, low-dimensional (LD) materials based saturable absorbers (SAs) are gaining popularity in pulsed laser applications due to their high nonlinearity, strong light-matter interaction, and low cost. Here, high-quality LD-SAs have been created by transferring 2 H-TaS 2 onto gold mirrors and covered with plasma-enhanced chemical vapor deposition (PECVD) SiO 2 layers. The non-linear transmission of SiO 2 passivated TaS 2 -SAM was measured using a balanced dual-detector technology. The modulation depth and saturated intensity were ~8.4% and 0.86 MW·cm −2 . Based on the SiO 2 passivated TaS 2 -SAM, Q-switched and mode-locked Erbium-doped (Er 3+ -doped) fiber pulse lasers have been successfully achieved. Stable soliton pulses are obtained in erbium-doped fiber lasers (EDFLs) with pulse width of 1.8 ps, repetition rate of 3.4 MHz and a center wavelength of 1560.6 nm. Moreover, the mode-locking laser exhibited long-term stability with high signal-to-noise ratio of 63 dB. This study serves as a standard for low-dimensional materials research in photonics applications, and the results reveal that TaS 2 -SAM has a wide range of applications in multifunctional all-fiber lasers.

Nonlinear optical properties of MXene and applications in broadband ultrafast photonics

As a typical kind of two-dimensional transition metal carbides, nitrides and/or carbonitrides (MXene), Ti 3 C 2 T x has attracted extensive attention in optoelectronic field owing to their outstanding thermal, optoelectronic, and nonlinear optical properties. Ti 3 C 2 T x has been widely used as saturable absorber (SA) for achieving ultrafast pulses, whereas the influence of recovery time on its nonlinear optical properties as SA in laser needs further exploration. Herein, the ultrafast dynamics and nonlinear optical properties of Ti 3 C 2 T x are investigated by the methods of transient absorption and balanced twin-detector measurements. According to the experimental results, Ti 3 C 2 T x has a bleaching recovery time more than 160 ps, resulting in a low saturation intensity. The prepared Ti 3 C 2 T x is utilized as SA to achieve Q-switched pulses at 1- and 1.5- μ m bands. This study demonstrates that ultrafast dynamics has a significant impact on adjusting and optimizing nonlinear optical parameters of MXenes, as well as designing new photonic devices. • Optical properties and applications of Ti 3 C 2 T x as saturable absorber (SA) in 1- and 1.5- μ m lasers were studied. • Effect of carrier dynamics of Ti 3 C 2 T x on saturable absorption performance was discussed. • Ti 3 C 2 T x as SA in lasers was quantitatively analyzed, benefiting for realizing customized SA. • Large-energy Q-switched pulses were realized in 1- and 1.5- μ m bands owing to low saturable intensity.