Giant saturation absorption of tungsten trioxide film prepared based on the seedless layer hydrothermal method

Nonlinear materials have gained wide interest as saturable absorbers and pulse compression for pulsed laser applications due to their unique optical properties.This work investigates the third-order nonlinear phenomenon of tungsten trioxide(WO_(3))thin films.The giant nonlinear absorption and nonlinear refractive index of WO_(3)thin films were characterized by Z-scan method at 800 nm.We experimentally observed the giant saturable absorption(SA)and nonlinear refractive index of WO_(3)thin films prepared by the seedless layer hydrothermal method,with SA coefficient being as high as-2.59×105cm·GW^(-1).The SA coefficient is at least one order of magnitude larger than those of the conventional semiconductors.The nonlinear refractive index n_(2)of WO_(3)film has been observed for the first time in recent studies and the corresponding coefficient can be up to 1.793 cm^(2)·GW^(-1).The large third-order nonlinear optical(NLO)response enables WO_(3)thin films to be promising candidates for optoelectronic and photonic applications in the near-infrared domain.

The Reverse Saturation Absorption Property of Indanthrone and Its Derivatives

The syntheses of three nonlinear reverse saturation absorption compounds-Indanthrone and its two derivatives are discussed. The properties of nonlinear reverse saturable absorption of the compounds were studied hy using the Z-scanning technique , and the influences of its conjugated structure on the absorption threshold value and the absorbable light density were discussed based on the reverse saturation absorption principle. The results shows that when the structure＇s conjugation property of Indanthrone and its derivatives becomes more poweoful , its absorption threshold reduees, the light lowest transmittance increases.

Direct detection of the transient superresolution effect of nonlinear saturation absorption thin films

Using a strong nonlinear saturation absorption effect is one technique for breaking through the diffraction limit. In this technique, formation of a dynamic and reversible optical pinhole channel and transient superresolution is critical. In this work, a pump–probe transient detection and observation–experimental setup is constructed to explore the formation process directly. A Ge2Sb2Te5 thin film with strong nonlinear saturation absorption is investigated. The dynamic evolution of the optical pinhole channel is detected and imaged, and the transient superresolution spot is directly captured experimentally. Results verify that the superresolution effect originates from the generation of an optical pinhole channel and that the formation of the optical pinhole channel is dynamic and reversible. A good method is provided for direct detection and observation of the transient process of the superresolution effect of nonlinear thin films.

Two-photon absorption of FAPbBr_(3) perovskite nanocrystals

Perovskite nanocrystals(NCs) with high two-photon absorption(TPA) cross-section are of great interest due to their potential applications in three-dimensional optical data storage and multiphoton fluorescence microscopy. Among various perovskite materials, FAPbBr_(3) NCs show a better development prospect due to their excellent stability. However, there are few reports on their nonlinear optical properties. In this work, the nonlinear optical behavior of FAPbBr_(3) NCs is studied.The methods of multiphoton absorption photoluminescence saturation and open aperture Z-scan technique were applied to determine the TPA cross-section of FAPbBr_(3)NCs, which was around 2.76 × 10^(-45)cm^(4)·s·photon^(-1) at 800 nm. In addition,temperature-dependent photoluminescence induced by TPA was investigated, and the small longitudinal optical phonon energy and electron–phonon coupling strength was obtained, which confirm the weak Pb–Br interaction. Meanwhile, it is found that the exciton binding energy in FAPbBr_(3) NCs was 69.668 me V, which may be ascribed to the strong hydrogen bond interaction. It is expected that our findings will promote the application of FAPbBr_(3) NCs in optoelectronic devices.

Saturated absorption spectrum of cesium micrometric-thin cell with suppressed crossover spectral lines

Micrometric-thin cells(MCs)with alkali vapor atoms have been valuable for research and applications of hyperfine Zeeman splitting and atomic magnetometers under strong magnetic fields.We theoretically and experimentally study the saturated absorption spectra using a 100-μm cesium MC,where the pump and probe beams are linearly polarized with mutually perpendicular polarizations,and the magnetic field is along the pump beam.Because of the distinctive thin chamber of the MC,crossover spectral lines in saturated absorption spectra are largely suppressed leading to clear splittings of hyperfine Zeeman transitions in experiments,and the effect of spatial magnetic field gradient is expected to be reduced.A calculation method is proposed to achieve good agreements between theoretical calculations and experimental results.This method successfully explains the suppression of crossover lines in MCs,as well as the effects of magnetic field direction,propagation and polarization directions of the pump/probe beam on saturated absorption spectrum.The saturated absorption spectrum with suppressed crossover lines is used for laser frequency stabilization,which may provide the potential value of MCs for high spatial resolution strong-field magnetometry with high sensitivity.

An approach to gas sensors based on tunable diode laser incomplete saturated absorption spectra

A spectral profile reconstruction method that can be applied to incomplete saturated-absorption spectra is proposed and demonstrated. Through simulation and theoretical calculation, it is proved that compared with the traditional wholeprofile fitting method, this new method can increase the concentration detection upper limit of a single absorption line by about 8.7 times. High-concentration water vapor is measured using TDLAS technology, the total water vapor pressure and the self-broadened half-width coefficient of the spectrum were simultaneously measured from incomplete saturatedabsorption spectra and compared with high-precision pressure sensors and the HITRAN databases. Their maximum relative deviations were about 4.63% and 9.10%, respectively. These results show that the spectral profile reconstruction method has great application potential for expanding the dynamic range of single-line measurements to higher concentrations,especially for in-situ online measurements under complex conditions, such as over large temperature and concentration dynamic ranges.

Characterization and Saturable Absorption Property of Graphene Oxide on Optical Fiber by Optical Deposition

We prepared graphene oxide（GO） saturable absorber（SA） successfully through optical deposition method, which is a simple but effective approach to deposit various materials onto substrate under the effects of light, and investigated several factors that influence the optical deposition result of GO onto optical fiber end, including poly（methyl methacrylate）（PMMA） concentration, light intensity, light mode, and deposition time. The efficient optically deposited GO preserving its nonlinearity guaranteed by GO/PMMA composite formation was also demonstrated. The GO SA prepared by optical deposition shows superior saturable absorption property with modulation depth and nonsaturable loss of 6% and 40%, respectively.

Laser shaping and optical power limiting of pulsed Laguerre–Gaussian laser beams of high-order radial modes in fullerene C60

We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a noncentrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect;the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.

In situ temperature measurement of vapor based on atomic speed selection

We demonstrate an experimental method for the in situ temperature measurement of atomic vapor using the saturated absorption spectrum. By separately manipulating the frequency of the pump and probe beams, the position of the crossover peaks can move along the spectrum. Different velocity classes of atoms contribute to the crossover during the movement. We study the relationship between the intensity change of peaks and vapor temperature. Our experimental result around room temperature shows a deviation of less than 0.3 K. Compared with traditional thermometry using absorption spectroscopy, higher accuracy can theoretically be achieved with real-time thermometry.

Saturable absorption and visible pulse modulation of few-layer topological nodal-line semimetal HfGeTe

Topological nodal-line semimetals attract growing research attention in the photonic and optoelectronic fields due to their unique topological energy-level bands and fascinating nonlinear optical responses.Here,to the best of our knowledge,we first report the saturable absorption property of topological nodal-line semimetal HfGeTe and the related pulse modulation in passively Q-switched visible lasers.Few-layer HfGeTe demonstrates outstanding saturable absorption properties in the visible-light band,yielding the saturation intensities of 7.88,12.66,and 6.64μJ/cm^(2)at 515,640,and 720 nm,respectively.Based on an as-prepared few-layer HfGeTe optical switch and a Pr:LiYF_(4)gain medium,Q-switched visible lasers are also successfully achieved at 522,640,and 720 nm.The minimum pulse widths of the green,red,and deep-red pulsed lasers are150,125.5,and 420 ns,respectively.Especially for the green and red pulsed laser,the obtained pulse width is smaller than those of the low-dimensional layered materials.Our work sheds light on the application potential of topological nodal-line semimetals in the generation of visible pulsed lasers.

800nm Semiconductor Absorber with Low Temp erature Method and Surface State Method Combined Absorber for Kerr Lens Modelocking of Ti:Al_2O_3 Laser

A novel 800nm Bragg mirror type of semiconductor saturable absorption mirror wit h low temperature method and surface state method combined absorber is presented .With which passive Kerr lens mode locking of Ti∶Al 2O 3 laser pumped by argo n ion laser is realized,which produces pulses as short as 40fs.The spectrum band width is 56nm,which means that it can support the modelocking of 20fs.The pulse frequency is 97.5MHz;average output power is 300mW at the pump power of 4.45W.

Impacts of Excessive Soaking on N, P, and K in Substrates Plots and Seedling Growth

[Objective] The aim was to study on impacts of excessive soaking N, P, and K insubstrate plots of and seedling growth. [Method] Substrate was designed to add additional 1/2 water after saturation and expansion. Disposable excessive soak- ing and regression relation of nutrition infusion of substrate plots were studied by design of 13 time gradient. Plant nutrition absorption and growth effects after sub- strate plots immersed by water were investigated by growing tomato. [Result] Con- centration and time of the three nutrition immersed in water had the regression equation of each, as follows： N=-2E-05t2＋0.016 lt＋2.0553, P=0.002 2t＋2.248 5 and K=0.004 7t＋0.875 8. With nutrition loss of the three, however, loss amount was al- most same with variance analysis of regression equation, which may result from its volatilization. Regression equations of P and K were： P=0.125 7t-0.117, and K=0.022 5t.1514, which led to adverse impact on plant absorption of N and K above ground, whose equations were N=20.64e-4E-0.4t, and K=E-06t2-0.011 3t＋29.055. Meanwhile, un- der the condition, sound seedling index was not impacted a lot by excessive immer- sion. [Conclusion] This study has provided theoretical reference for guidance of sub- strate plot soaking method, cultivation and regulation, and breeding, as well as agri- cultural production.

Phase-modulated quantum-sized TMDs for extreme saturable absorption

Two-dimensional semiconductors such as transition metal dichalcogenides(TMDs)have attracted much interest in the past decade.Herein,we present an all-physical top-down method for the scalable production of the intrinsic TMD quantum sheets(QSs).The phases of the TMDs(e.g.,2H-MoSe_(2),2H-WSe_(2),and Td-WTe2)remain stable during the transformation from bulk to QSs.However,phase transition(from Td to 2H)is detected in MoTe2.Such phase-modulation by size-reduction has never been reported before.The TMD QSs can be well dispersed in solvents,resulting in remarkable photoluminescence with excitation wavelength-,concentration-,and solvent-dependence.Meanwhile,the TMD QSs can be readily solution-processed into hybrid thin films,which demonstrate exceptional nonlinear saturation absorption(NSA).Notably,2H-MoTe2 QSs in poly(methyl methacrylate)show extremely high NSA performance with(absolute)modulation depth up to 46.6%and saturation intensity down to 0.81 MW·cm^(−2).Our work paves the way towards quantum-sized TMDs.

Tailoring optical properties of TiO_2 in silica glass for limiting applications

We present the linear and nonlinear optical studies on TiO2-SiO2 nanocomposites with varying compositions. Opti- cal band gap of the material is found to vary with the amount of SiO2 in the composite. The phenomenon of two-photon absorption （TPA） in TiO2/SiO2 nanocomposites has been studied using open aperture Z-scan technique. The nanocom- posites show better nonlinear optical properties than pure TiO2, which can be attributed to the surface states and weak dielectric confinement of TiO2 nanoparticles by SiO2 matrix. The nanocomposites are thermally treated and similar studies are performed. The anatase form of TiO2 in the nanocomposites shows superior properties relative to the amorphous and rutile counterpart. The involved mechanism is explained by rendering the dominant role played by the excitons in the TiO2 nanoparticles.

Functional nonlinear optical nanoparticles synthesized by laser ablation

Nonlinear optics is an important research direction with various applications in laser manufacturing,fabrication of nano-structure,sensor design,optoelectronics,biophotonics,quantum optics,etc.Nonlinear optical materials are the funda-mental building blocks,which are critical for broad fields ranging from scientific research,industrial production,to military.Nanoparticles demonstrate great potential due to their flexibility to be engineered and their enhanced nonlinear optical properties superior to their bulk counterparts.Synthesis of nanoparticles by laser ablation proves to be a green,efficient,and universal physical approach,versatile for fast one-step synthesis and potential mass production.In this review,the development and latest progress of nonlinear optical nanoparticles synthesized by laser ablation are summarized,which demonstrates its capability for enhanced performance and multiple functions.The theory of optical nonlinear absorption,experimental process of laser ablation,applications,and outlooks are covered.Potential for nanoparticle systems is yet to be fully discovered,which offers opportunities to make various types of next-generation functional devices.

Nonlinear optical trapping effect with reverse saturable absorption

Nonlinear responses of nanoparticles induce enlightening phenomena in optical tweezers. With thegradual increase in optical intensity, effects from saturable absorption (SA) and reverse SA (RSA) arise insequence and thereby modulate the nonlinear properties of materials. In current nonlinear optical traps,however, the underlying physical mechanism is mainly confined within the SA regime because thresholdvalues required to excite the RSA regime are extremely high. Herein, we demonstrate, both in theory andexperiment, nonlinear optical tweezing within the RSA regime, proving that a fascinating composite trappingstate is achievable at ultrahigh intensities through an optical force reversal induced through nonlinearabsorption. Integrated results help in perfecting the nonlinear optical trapping system, thereby providingbeneficial guidance for wider applications of nonlinear optics.

Optical Limiting Response in Er^(3+)-Doped TeO_2-Nb_2O_5-ZnO Glass

The nonlinear absorption properties of Er^3＋ doped telluride glass were investigated with picosecond laser pulses. The optical limiting response was measured with a transmission technique and reverse saturable absorption （RSA） with a Z-scan technique, which proved that the glass was a promising material for practical optical limiters. The experimental resulted showed that the excited absorption was responsible for the measured RSA, resulting in the optical limiting response. The measured data could be well simulated with a rate equation model to obtain the absorption cross sections of the excited state.

Preparation & Properties Research of Two Indium Phthalocyanine Materials

Two iodo（phthalocyainato） indium complexes were synthesized and mixed with polymer solution（PMMA/chloroform）to prepare iodo（phthalocyainato）indium/PMMA compound film materials on a glass slice by the method of dipping film.Two materials have typical B-band and Q-band absorption of Phthalocyanine compounds in the UV-Vis spectrum.The reverse saturable absorption experiments show that two materials have better reverse saturable absorption properties while they have higher linear transmissivity.In addition,the highest transmittance of visible light is over 70%（tetrakis（cumylphenoxy）phthalocyainate indium/OMMA compound film material）.The initial threshold is 127.1mJ/cm^2.The dynamic range is 1.43.It can be concluded that introduction of the substituted groups having bigger steric hindrance and conjugative effect in the Phthalocyanine ring may increase the reverse saturable absorption effect of the Phthalocyanine indium material.

Nonlinear optical properties of an azobenzene polymer

The nonlinear optical properties of an azobenzene polymer azol2-MO were investigated by a Z-scan technique. The polymer was synthesized by assembling the liquid-crystalline polymer azol2 with methyl orange. The nonlinear refrac- tive index （1.39×10^-15 cm2/W） and the nonlinear absorption coefficient （0.11 cm/GW） of azol2-MO were determined with 532-nm picosecond laser pulses at the irradiance of 92.40 GW/cm2. When compared to the nonlinear properties of azol2 and methyl orange, azol2-MO possesses the advantages of its two constituents and shows larger nonlinear optical properties.

Electronic and optical properties of TiO_2 and its polymorphs by Z-scan method

TiO2 is a material which has attracted considerable attention from the scientific community for its innumerable prop- erties. TiO2 is known to exist in nature in three different crystalline structures： rutile, anatase, and brookite. Anatase and rutile TiO2 films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO2 and its polymorphs, anatase, and rutile, prepared by the sol-gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of Z（3） for amorphous, anatase, and rutile are also calculated and found to be 5 × 10^-19 m2/V2, 27 × 10^-19 m2/V2, 19 × 10^-19 m2/V2, respectively. It is found that the values of the optical constants of amorphous TiO2 after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO2 synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO2 is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.