Laser Excitation Research Articles

Near-infrared photothermal lens as microfluidic analyzer for determination of phosphate in food and biological samples

In this work, photothermal lens spectrophotometer (PTLS) with crossed-beam configuration pumped by a laser diode (850 nm) was used for determination of soluble phosphorus exists mainly in the form of orthophosphate (PO43−) in nonalcoholic beverage and human blood serum samples. The determination was carried out after complexation reaction between blue molybdenum and phosphate in aqueous solution. UV–vis spectrophotometry was used by measuring absorption in the near infrared region (815 nm) for optimizing the complex formation time, concentrations of reducing agent and sulfuric acid. The UV–vis absorption measurements showed that the calibration curve was obtained in the concentration ranges of 0.5–80 mg L−1 with a linear correlation coefficient of 0.98 and a detection limit of 0.2 mg L−1. Then, PTLS at a wavelength of 850 nm after optimizing the device conditions (flow rate, excitation laser power and interrupting frequency) was used for phosphate determination. The calibration curve in the concentration range of 11–1000 µg L−1 has a correlation coefficient of 0.98 and a detection limit of 4 µg L−1. The achieved detection limit was about 50 times better than NIR absorption spectrometry using a conventional 1 cm sample cell. In PTLS with the 3 μL microfluidic cell experimental detectability amount of phosphate is 33 picogram, while in UV–vis-NIR method this amount is 1.5 µg.

Photon avalanche effect and spectral control of single LiYF4:Yb3+/Pr3+microparticle

Photon avalanche is a special phenomenon of upconversion that the luminescence emission intensity exhibits a significant nonlinear response to the excitation power. Traditional photon avalanche is typically observed in bulk materials, which is not enough to meet requirements of modern techniques as it expect smaller in size and stronger in signal response. In this study, photon avalanche effect is obtained from single LiYF4: Yb3+/Pr3+ microparticle. The emission intensity demonstrates a 16-order nonlinear coefficient with excitation intensity change under 835 nm laser excitation. By utilizing the plasmonic effect of noble metal nanoparticles, we successfully modulate the photon avalanche of the particle. Obvious reduction in the threshold of photon avalanche is detected when plasmonic gold nanorods are assembled to the surface of LiYF4: Yb3+/Pr3+ microparticle.

Power dependent tunable optical nonlinearity in Iron oxide/Borophene core-shell nanoparticles under ultrashort laser excitation

Two-dimensional (2D) nanomaterials find immense applications in ultrafast photonics and optical switching systems due to their fascinating nonlinear optical (NLO) characteristics. This work presents a systematic investigation of laser power-dependent nonlinear optical characteristics of borophene nanosheets in a core-shell nanostructure. For this purpose, we have synthesized Borophene encapsulated Iron oxide (Fe3O4) core-shell nanoparticles (Fe3O4/Borophene CSNPs). The CSNPs were synthesized by mixing and annealing sodium borohydride (NaBH4) as a boron precursor with iron oxide nanoparticles (Fe3O4 NPs) in a controlled environment using chemical vapor deposition technique (CVD) followed by characterization using XRD, FTIR Spectroscopy, UV–vis absorption spectroscopy, TEM, SEM, and EDX techniques. Magnetic properties were analyzed by a vibrating sample magnetometer (VSM) which shows that the saturation magnetization of Fe3O4 NPs increases after being encapsulated in borophene nanosheets. The role of borophene in modifying the NLO characteristics of Fe3O4/Borophene CSNPs was studied using a power-dependent Z-scan technique utilizing ultrashort (femtosecond) laser pulses at a wavelength of 800 nm in both open and close aperture configuration. It was found that borophene-coated Fe3O4 NPs reveal tunable NLO properties that resemble the NLO characteristics of borophene nanosheets with enhanced features. This provides insights into an interaction between materials in NLO phenomena and illustrates the distinctive performance of the core-shell nanostructure. The tunable NLO properties of Fe3O4/Borophene CSNPs offer an innovative approach for developing optoelectronics and ultrafast nonlinear photonic devices.

Photonic-Cavity-Enhanced Laser Writing of Color Centers in Diamond.

Color centers in diamond have widespread utility in quantum technologies, but their creation process remains stochastic in nature. Deterministic creation of color centers in device-ready diamond platforms can improve the yield, scalability, and integration. Recent work using pulsed laser excitation has shown impressive progress in deterministically creating defects in bulk diamond. Here, we extend this laser-writing process into nanophotonic devices etched into diamond membranes, including nanopillars and photonic resonators with writing and subsequent readout occurring in situ at cryogenic temperatures. We demonstrate the optically driven creation of carbon vacancy (GR1) and nitrogen vacancy (NV) centers in diamond nanopillars and observe enhanced photoluminescence collection from them. We also fabricate bullseye resonators and leverage their cavity modes to locally amplify the laser-writing field, yielding defect creation with picojoule write-pulse energies 100 times lower than those typically used in bulk diamond demonstrations.

Enhancement of upconversion luminescence in NaBiF4: Er3+/Yb3+/Lu3+ for temperature detection

Optical thermometer has got lots of attention by virtue of non-contact, fast response speed, high sensitivity, anti-interference ability, which is less affected by the environment. However, most fluorescent thermometers still suffer from low sensitivity. Here, an optical thermometer based on NaBiF4: Er3+/Yb3+/Lu3+ with enhanced upconversion luminescence is reported. The sample emits strong green light of Er3+ under 980 nm laser excitation and with the increase of Lu3+, the whole luminescence intensity of NaBiF4: 2 % Er3+/20 % Yb3+/ 2.5 % Lu3+ is enhanced by about 3 times, which due to local crystal field distortion. Meanwhile, the lifetime of Er3+ is prolonged and the temperature detection performance is also improved with the substitution of Lu3+. The relative sensitivity reaches a maximum of 0.841 % K−1 at 301 K. The results suggest that it is an optical nanothermometer with great potential.

Raman characterization of lunar highlands simulants for in-situ resource utilization in a lunar setting

Lunar regolith simulants from the NU-LHT series were characterized using different configurations for performing Raman spectroscopy measurements, including with different excitation wavelengths and spot sizes. This testing was performed to explore various Raman measurement configurations for analyzing lunar regolith, especially in terms of capturing distinctive fluorescence features that can provide more information about the composition of the regolith. Results obtained utilizing configurations having a 785 nm laser for excitation showed relatively narrow, intense fluorescence signals between 870 and 890 nm, which, to the best of our knowledge, has not been observed before in lunar regolith or lunar simulant samples. These distinctive fluorescence features, attributed to a specific rare earth element (REE) impurity, adds further support that these types of features can be utilized for identification and potentially quantification of the amount of REE or transition metal impurities in lunar regolith. Further, other aspects of these Raman instrument configurations and their advantages were explored, especially those applicable for use in a lunar environment in support of in-situ resource utilization (ISRU).

Digital Holographic Interferometry for Micro-Deformation Analysis of Morpho Butterfly Wing

In this study, we present an analysis of deflections in a Morpho butterfly wing using digital holographic interferometry (DHI). Our methodology revolves around an off-axis lensless Fourier holographic setup, using laser excitation to induce deflections in the object. The implementation of a DHI setup, tailored for rapid monitoring of micro-deformation, is a central aspect of our research. We offer an overview of the theoretical foundations of this technique, complemented by both experimental and numerical results aimed at validating our findings. We designed an optical setup that enhanced both laser illumination and hologram reconstruction for the sample. The experimental findings decisively show that the proposed method is effective for rapid deformation analysis. The deformation of the wing can be measured with micro-meter accuracy thanks to numerical analysis.

Part-per-Billion (Ppb)-Level Acetylene Sensor Employing Optical Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) with an Erbium-Doped Fiber Amplifier (EDFA) and a Fiber-Optic Fabry–Perot Interferometer

An all-optical double-pass quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for the detection of acetylene (C2H2) at part-per-billion (ppb) levels was developed and experimentally validated. By employing an erbium-doped fiber amplifier (EDFA) capable of emitting up to 1 W of optical power, a commercial quartz tuning fork (QTF) resonating at 30.7 kHz, and double-pass acoustic microresonators, the amplitude of the QEPAS signal was significantly enhanced, thereby improving the sensitivity of the C2H2-QEPAS sensor. Instead of using piezoelectric detection in conventional QEPAS, a highly sensitive fiber-optic Fabry–Perot interferometer (FPI) was employed to measure the vibration of the QTF prong. A working point self-stabilizing technique was exploited to improve the demodulation sensitivity and stability. The linear response of the sensor to laser power and C2H2 concentration confirmed that no saturation occurred. With an excitation laser power of 1 W and a C2H2 absorption line of 1532.83 nm, a C2H2 minimum detection limit (MDL) of 19.1 ppb was achieved, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 1.58 × 10−8 cm−1∙W∙Hz−1/2. Owing to its high sensitivity, long-term stability, and immunity to electromagnetic interferences, the QEPAS sensor provides considerable potential for remote gas sensing in environmental monitoring and other applications.

Reversible pH-switchable NIR-II nano-photosensitizer for precise imaging and photodynamic therapy of tumors

Photodynamic therapy (PDT) has attracted widespread attention from researchers as an emerging cancer treatment method. There have been many reports on various types of NIR-II photosensitizers for imaging and treatment of tumor sites. However, there are few reports on the development of NIR-II organic small molecule photosensitizers that have intelligent response to the tumor microenvironment, precise imaging, real-time treatment, and high biocompatibility. In this work, we developed a series of NIR-II photosensitizers (RBTs) with near-infrared excitation, good photostability, and large Stokes shift. Among them, RBT-Br exhibited higher reactive oxygen species (ROS) generation efficiency due to the introduction of halogen heavy atoms to enhance intersystem crossing (ISC). It is noteworthy that RBT-Br can generate singlet oxygen (1O2) and superoxide anion radicals (•O2−) simultaneously under 730 nm laser. Subsequently, we used molecular engineering technology to construct three pH-responsive NIR-II photosensitizers (RBT-pHs) by utilizing the closure of the lactam ring, among which RBT-pH-1 (pKa = 6.78) is able to be directionally activated under the stimulation of tumor micro-acid environment, with its fluorescence emission window reaching 933 nm. Subsequently, RBT-pH-1 NPs encapsulated in DSPE-mPEG5k were applied for PDT treatment of mouse tumors. The results showed that RBT-pH-1 NPs were activated by the acidic tumor microenvironment and generated ROS under laser excitation, exhibiting precise tumor imaging and significant tumor growth inhibition. We look forward to these multifunctional NIR-II organic small molecule photosensitizers providing a more efficient approach for clinical treatment of tumors. Statement of significanceA reversible pH-switchable NIR-II nano-photosensitizer RBT-pH-1 NPs (pKa = 6.76) is developed for precise imaging and PDT therapy of mouse tumors, which can be effectively used for targeted enrichment and activation of tumor micro-acid environments. The results show that this NIR-II photosensitizer generates ROS through tumor micro-acid environment stimulation and laser triggering, showing precise tumor imaging guidance and significant tumor growth inhibition.

Discrimination of vibrational modes in Ni2MnGa thin films

Vibrational properties in magnetic shape memory alloys are intrinsically connected to the topologies formed due to temperature-dependent breakdown of symmetry. In this sense, herein, we apply Raman spectroscopy in the study of Ni2MnGa films prepared by sputtering on glass and gallium arsenide substrates. Different laser wavelengths probe the Raman active vibrational modes. The non-equilibrium heating mechanisms of the electronic lattice induced by excitation laser power within the thermal penetration depth are used to explain the formation of higher order vibrational modes resulting from phonon-assisted intra-band electronic excitations. The discrimination of the Raman active modes is performed based on calculations carried out within the framework of the density functional theory considering the coexistence of austenite and martensite phases as a function of temperature in films with different crystalline textures and residual stresses. More importantly, this work presents a simple way to discriminate the vibrational modes of the austenite and martensite phases in Ni2MnGa thin films that can be easily applied in the nanodevice development process.

A Multi-Institutional Study of Magnetic Resonance/Ultrasound Fusion-Guided Nanoparticle-Directed Focal Therapy for Prostate Ablation.

Focal therapy aims to provide a durable oncologic treatment option for men with prostate cancer (PCa), while preserving their quality of life. Most focal therapy modalities rely on the direct tissue effect, resulting in a possible nontargeted approach to ablation. Here, we report the results of the first human feasibility trial utilizing nanoparticle-directed focal photothermal ablation for PCa. A prospective, open-label, single-arm, multicenter study of men with localized PCa in Gleason Grade Group 1 to 3 was conducted. Men received a single infusion of gold nanoparticles (AuroShells), followed by magnetic resonance (MR)/ultrasound (US) fusion-guided laser excitation of the target tissue to induce photothermal ablation. MRI was used to assess the effectiveness of prostate tissue ablation at 48 to 96 hours, 3 months, and 12 months post treatment. At 3 months, a targeted fusion biopsy of the lesion(s) was conducted. At 12 months, a targeted fusion biopsy and standard templated biopsy were performed. Treatment success was determined based on a negative MR/US fusion biopsy outcome within the treated area. Forty-six men were enrolled in the study, and 44 men with 45 lesions completed nanoparticle infusion and laser treatment. The mean PSA level at baseline was 9.5 ng/mL, which decreased to 5.9 ng/mL at 3 months and to 4.7 ng/mL at 12 months (P < .0001). The oncologic success rates at 3 and 12 months resulted in 29 (66%) and 32 (73%) of 44 patients, respectively, being successfully treated, confirmed with negative MR/US fusion biopsies within the ablation zone. Among Gleason Grade Group, maximum lesion diameter on MRI, prostate volume, and Prostate Imaging Reporting and Data System scoring, the maximum lesion diameter was significantly associated with the odds of treatment failure at 12 months (P = .046). Nanoparticle-directed focal laser ablation of neoplastic prostate tissue resulted in 73% of patients with successful treatment at 12 months post treatment, confirmed by negative MR/US fusion biopsy of the treated lesion and a systematic biopsy. 02680535.

Unveiling the Influence of Brightness Heterogeneity in Fluorescence Correlation Spectroscopy of Perovskite Nanocrystals.

Nanoparticles (NPs), including perovskite nanocrystals (PNCs) with single photon purity, present challenges in fluorescence correlation spectroscopy (FCS) studies due to their distinct photoluminescence (PL) behaviors. In particular, the zero-time correlation amplitude [g2(0)] and the associated diffusion timescale (τD) of their FCS curves show substantial dependency on pump intensity (IP). Optical saturation inadequately explains the origin of this FCS phenomenon in NPs, thus setting them apart from conventional dye molecules, which do not manifest such behavior. This observation is apparently attributed to either photo-brightening or optical trapping, both lead to increased NP occupancy (N) in the excitation volume, consequently reducing the g2(0) amplitude [since g2(0) α 1/N] at high IP. However, an advanced FCS study utilizing alternating laser excitation at two different intensities dismisses such possibilities. Further investigation into single-particle blinking behaviors as a function of IP reveals that the intensity dependence of g2(0) primarily arises from the brightness heterogeneity prevalent in almost all types of NPs. This report delves into the complexities of the photophysical properties of NPs and their adverse impacts on FCS studies.

Temperature Field Measurements in Swirl Spray Flames Using Two-Line Planar Laser Induced Fluorescence Thermometry

Abstract This paper investigates the temperature fields in a centrally staged swirl spray combustor using two-line OH planar laser induced fluorescence (PLIF) thermometry at elevated inlet pressures and temperatures up to 0.62 MPa and 650 K. The pilot and main stages of the combustor were supplied with RP-3 kerosene. OH radicals were excited using the Q1(5) and Q1(14) transitions within the A2Σ←X2Π (1,0) band. Two laser excitation systems were operated simultaneously, where the two beams were spatially combined and separated by a small interval in time. The PLIF signals excited at the two wavelengths were captured by two identical sets of imaging system. The calibration coefficient needed for quantitative conversion from fluorescence ratio to temperature was determined based on results from independent coherent anti-Stokes Raman scattering (CARS) measurements. A joint threshold mask was developed to remove the noise and weak signals in the raw PLIF images. The high temperature zones in the temperature field were then obtained, and the pilot and main stage flames were identified. In addition, the radial position of the pilot flame showed marked variations at a nominally fixed condition. By extracting the radial profiles, a consistency between the peaks of PLIF intensity and temperature was found, suggesting that PLIF images could be a qualitative substitute for the high temperature zones in the temperature fields of these swirl spray flames. This study demonstrates the feasibility of temperature field measurements using two-line OH PLIF in aero-engine model combustors.

Up-conversion optical temperature sensing characteristics of new KBaGd(MoO4)3:Yb3+,Ho3+ phosphors

To develop new up-conversion luminescent materials for non-contact optical thermometer with high sensitivity and temperature resolution, a battery of KBaGd(MoO4)3:Yb3+,Ho3+ phosphors were fabricated through solid reaction process. The crystal structure, up-conversion luminescence, energy transfer, thermal stability and optical temperature sensing performances were studied in detail. Under 980 nm laser excitation, the KBaGd(MoO4)3:Yb3+,Ho3+ phosphor exhibits distinctive emission bands of Ho3+ at 545, 660, and 755 nm, and excellent illuminant performance. Based on the thermally coupled levels (TCLs) of Ho3+, both the relative sensitivity (Sr) and absolute sensitivity (Sa) display similar change trends, with the highest values of 6.73%/K (@298 K) and 5.69%/K (@298 K), respectively. Furthermore, the highest Sa of 13.90%/K (@623 K) and the ultimate Sr of 0.62%/K (@ 298 K) are achieved based on non-TCLs of Ho3+. Therefore, KBaGd(MoO4)3:Yb3+,Ho3+ phosphor is a promising candidate for self-referenced optical thermometry.

Photoelectric properties of the semiconductor Bi2YbO4Cl with broad spectral response

Bi2YbO4Cl with a fluorite layer structure belongs to the family of the bismuth rare-earth oxyhalides Bi2REO4X (X=Cl, Br, I). However, the synthesis and photoelectric properties of Bi2YbO4Cl have almost not been reported. In this work, Bi2YbO4Cl was synthesized using the solid-state method and the solvothermal method. Yb3+ ions show a strong characteristic absorption peak at 980 nm, which was measured by ultraviolet–visible–near-infrared absorption spectra. The transient photoconductivity of Bi2YbO4Cl was obtained by time-resolved terahertz spectroscopy system under 400 and 800 nm laser excitations, respectively. The frequency-dependent transient photoconductivity analysis reveals the Drude-Smith behavior in Bi2YbO4Cl. Under photoexcitation, the hot charge carriers with a long relaxation lifetime and a carrier mobility of 48 cm2/(V·s) are obtained. The synthesis of Bi2YbO4Cl is of great significance for the development of novel photocatalytic and photoharvesting materials with broad spectral response.

An investigation on hydrodynamic behavior of horizontal gas–liquid intermittent flow by S-PLIF and parallel-wire conductance sensors

Horizontal gas–liquid two-phase flows widely exist in a variety of industrial fields such as the environment, chemical industry and energy. Intermittent flow, characterized by the quasi-periodic alternation motion of liquid slugs and large-scale Taylor bubbles, is the most prevalent flow pattern in horizontal gas–liquid two-phase flows. Comprehensive research on the hydrodynamic behavior of gas–liquid intermittent flow is essential for revealing the mass and heat transfer characteristics between phases, thereby establishing physical models of flow parameters. In this study, a structured planar laser-induced fluorescence (S-PLIF) system and paired parallel-wire conductance sensors (PWCSs) are designed to detect the gas–liquid interface structures and the hydrodynamic parameters. The S-PLIF system consists of a laser, a visualization box, a Ronchi ruling-plate and a pair of high-speed cameras. An optical linear prism forms a laser sheet in the transverse direction and the middle of the test section, and the cameras are positioned at 70° and 90° respectively to the plane of the laser sheet, referred to as S-PLIF70 and S-PLIF90. Under the laser excitation, bright and dark stripes generated by the Ronchi ruling-plate are deflected at the gas–liquid interface. The influence of total reflection can be effectively avoided by identifying the deflection position of the stripes, allowing for accurate detection of the gas–liquid interfacial structures. The effects of the interface fluctuations and detached bubbles on the S-PLIF70&90 results are investigated. Fluctuation and evolution characteristics of the gas–liquid interface are analyzed by probability density function (PDF) and power spectral density (PSD). Meanwhile, hydrodynamic parameters, i.e., Taylor bubble nose and tail velocity, Taylor bubble and slug length, and slug frequency, are detected by the PWCSs, and compared with previous correlations. The evolution characteristics of the interfacial structures and hydrodynamic parameters are uncovered as the flow condition changes.

New phase-construction phosphors ceramics for warm-white solid-state lighting: Orange-yellow-emitting (Lu,Gd)3(Sc,Al)5O12: Ce3+

Phosphor-converted white light-emitting diodes (pc-wLEDs) and phosphor-converted white laser diodes (pc-wLDs) are extensively utilized in lighting applications, with their quality and reliability heavily dependent on color converters. Recent progress in all-inorganic color converters, particularly phosphor ceramics (PCs), have markedly enhanced performance. However, due to the difficulty of managing emissive components, achieving warm white light with substantial red emission still remains challenging. In this work, a series of pure-phase Ce3+-activated garnet-structured solid-solution PCs, (Lu,Gd)3(Sc,Al)5O12: Ce (LGSAG: Ce), were fabricated using vacuum sintering technology for the first time. Through systematic analysis, it can be revealed that the addition of Gd3+ leads to a red shift in emission through changes in crystal-field splitting, whereas the inclusion of Sc3+ primarily focuses on improving the microstructure of the developed PCs. Particularly, the pc-wLED constructed from typical LGSAG: Ce PC generated significantly warmer light with a correlated color temperature (CCT) of 2916 K, compared to the 9557 K from LuAG: Ce PC. Meanwhile, under 40.0 W (15.7 W/mm2) blue laser excitation, the maximum luminous flux and luminescence efficiency of one typical LGSAG: Ce PG are 1172 lm and 29.3 lm/W, respectively. Therefore, the developed LGSAG: Ce PCs can show notable potential as color converters for future high-power warm-white solid-state lighting applications.

Polarized luminescence of bound excitons in Cu2O single crystal

Photoluminescence was studied for Cu2O (100) single crystal in the 1.2–1.9 eV spectral range under polarized laser excitation 532 nm at low temperature. Polarized luminescence and negative thermal quenching were detected for the emission bands at 1.34, 1.53 and 1.7 eV, assigned to the bound excitons localized at copper vacancies VCu and oxygen vacancies VO+, VO2+, correspondingly. The complex structure of the most intense emission bands 1.34 and 1.7 eV containing spectrally shifted orthogonally polarized subbands was identified. Luminescence polarization degree, intensity and spectral position of the subbands depend on temperature as well as on the excitation light density and vary from point to point. The origin of the polarized luminescence and negative thermal quenching of the bound excitons in Cu2O crystal is discussed.

Impact of altering phase modulation and geometrical shape of laser beam via a phase-only spatial light modulator on laser-induced fluorescence

This study investigates the impact of modulating and shaping a laser beam via a phase-only spatial light modulator (SLM) on the intensity of the laser-induced fluorescence (LIF) signal. Different phase modulations ranging from 0 to 2π are applied to the SLM window to evaluate the effect of the modulated beam on the emitted LIF signal from extra virgin olive oil EVOO samples. The laser beam is also shaped into circular and square geometries with varying diameters to determine the optimum size for maximizing the LIF signal strength. The results reveal that the highest LIF signal intensity could be obtained after modulating the incident laser beam with phase shifts of 0 and 2π, with an improvement factor of approximately 3 for Avanti olive oil and 1.42 for Al Jouf olive oil. Furthermore, laser beam shaping into a circular aperture with a radius of 2.45 mm or a square aperture with a side length of 2.45 mm yields the highest LIF signal improvement, with enhancement factors of approximately 2.9 for Avanti olive oil and 1.42 for Al Jouf olive oil. This work demonstrates the potential of SLM-based beam shaping techniques to optimize LIF measurements by tailoring the wavefront characteristics of the excitation laser source.

Doping engineering of NiO–Zn nanofilms for modulation of morphological structure and ultrafast nonlinear optical response at 515 nm

In this work, to investigate the metal doping on the third-order nonlinear optical properties of NiO thin films under femtosecond pulsed laser excitation, pure NiO and 2w,4w,6w,8w Zn doped-NiO nanofilms were prepared by DC-RF co-sputtering technique. Then, the nonlinear absorption properties and nonlinear refractive properties of the five samples were investigated using the femtosecond laser at a wavelength of 515 nm. The experimental results show that the nonlinear absorption and nonlinear refractive properties of NiO are enhanced by the doped metal as well as the effect of defects. In addition, by varying the pump light intensity, we observed the transition of nonlinear absorption from the coexistence of saturated absorption and reverse saturated absorption to reverse saturated absorption. We established a multi-energy level system to interpret the nonlinear absorption and nonlinear refractive results, which broadens the application of NiO thin films in the field of nonlinear optics.