Negative Nonlinear Absorption Research Articles

Broad -band nonlinear optical response in Bi2Te0.6S2.4 alloys based on alloy engineering.

Alloy engineering plays an important role in regulating the optoelectronic properties of materials. This work demonstrates that Bi2Te0.6S2.4 alloys can extend nonlinear optical response to the near-infrared range. Te alloying at S sites can narrow the band gap, as proved by density functional theory (DFT) calculations, leading to a broadband saturable absorption response ranging from ultraviolet (350 nm) to near-infrared (1100 nm) wavelength with negative nonlinear optical absorption coefficient ranging from -0.12 cm GW-1 to -1.28 cm GW-1. Moreover, the broadband carrier dynamic of Bi2Te0.6S2.4 alloys was investigated via femtosecond transient absorption (TA) at an excitation of 325 nm. A faster carrier dynamic at near-infrared wavelength was observed because of an increase in electron density at the conduction band minimum due to the additional Bi-Te interaction, which was corroborated by DFT calculations. These results suggest that alloy engineering provides an effective way for the development of broadband nonlinear optical devices.

Using femtosecond laser pulses to explore the nonlinear optical properties of a CR-39 polymer after being exposed to alpha particles

The effect of alpha particle radiation on nonlinear optical properties of poly(allyl diglycol carbonate) (CR-39) polymer has been investigated using the Z-scan technique. CR-39 polymers were exposed to alpha particles at different doses: 23.7 and 47.5 Gy. Alpha particles cause significant optical and chemical changes in the polymer CR-39. Data from UV-visible spectrometers revealed that when alpha particle doses increased, the absorption edge of polymer redshifted and the energy band gap decreased. Fourier transform infrared absorption spectra of alpha irradiation samples show a change in intensity and bond breakage in the chemical groups constituting the CR-39 polymer compared to the pristine one. With 100 fs laser pulses and 80 MHz repetition rate, the nonlinear absorption coefficient and nonlinear refractive index are measured for a pristine and irradiated polymer with different alpha doses at different excitation wavelengths and laser peak power. The samples displayed a negative nonlinear refractive index and reverse saturable absorption behavior with three photons absorption. The results reveal that the nonlinear optical properties of CR-39 were enhanced by alpha particle radiation.

Radiation-induced negative optical nonlinearities in fused silica, sapphire, and borosilicate glass

Negative nonlinear absorption is reported in neutron- and gamma-irradiated high-OH content fused silica, low-OH content fused silica, sapphire, borosilicate glass, and radiation-resistant borosilicate glass irradiated to total neutron fluences of 3.4 × 1016 n ⋅ cm−2 (42 Mrad γ), 1.7 × 1017 n ⋅ cm−2 (211 Mrad γ), and 3.6 × 1017 n ⋅ cm−2 (433 Mrad γ). Nonlinear absorption coefficients were measured via Z-scan and are on the order of −(10−14−10−10) m⋅W−1. The Z-scan also reveals a negative nonlinear index of refraction in neutron- and gamma-irradiated radiation-resistant borosilicate glass on the order of −10−19 m⋅2W−1. Thermal annealing at temperatures up to 800∘C is shown to restore these nonlinearities to their positive unirradiated values in all four materials. All Z-scan measurements were performed at 532 nm with a nanosecond pulsed laser. The occurrence of negative nonlinearities may be attributed to the presence of metallic impurities and the resulting saturable absorption. A limited effect of photobleaching is observed in measurements and is quantified in multiple Z-scans.

Synthesis, band gap structure and third order non-linear optical properties of zinc tungsten oxide nanocomposite using a single CW laser beam.

In this study, a composite of zinc tungsten oxide nanoparticles (W-ZnO NPs) has been synthesized via mixing Na2WO4 and zinc acetate in water, followed by dropwise addition of NaOH. The synthesized W-ZnO NPs were characterized using measurement methods such as XRD, dynamic light scattering (DLS), Scanning electron microscopy (SEM) and UV-Vis. Also, the results were compared with the pure synthesized ZnO and WO3 NPs. Non-linear optical properties of the synthesized composite were measured using the Z-scan technique with a continuous wave Nd-Yag laser. The negative non-linear absorption coefficient of the components was obtained which indicates that the saturation absorption occurred in this composite. In comparison with pure ZnO NPs, non-linear absorption decreases which can be attributed to the negligible optical response of WO3 structures. Also, the negative value of the close aperture Z-scan curve shows that the thermal lensing effect is the main reason for the third-order non-linear refraction.

Nonlinear optical properties and transient absorption in Hibiscus Sabdariffa dye solution probed with femtosecond pulses

Highly conjugated organic molecules are attractive chromophores for nonlinear optics due to their significant third-order nonlinear response near the absorption bands located in the broad spectral range from 200 to 900 nm. In this work, we report on the wavelength-dependence of one- and two-photon absorption processes in Hibiscus sabdariffa organic dye excited by femtosecond (fs) laser pulses centered at 1030 nm and 515 nm. Z-scan and transient absorption (TA) techniques have been employed to investigate the absorption and relaxation processes in the target dye. The dye is found to have a significant negative nonlinear absorption coefficient (β) of value ∼ −2.7 × 10−11 cm/W at 515 nm probing laser pulses, while it has a positive value equal to +2.1 × 10−13 cm/W when 1030 nm laser pulses were employed. The TA decay measurements using 40 fs laser pulses, centered at 515 nm wavelength, reveal that the dye exhibits a short relaxation time of ∼3 ps attributed to the involvement of the excited state proton transfer (ESPT) process in the Hibiscus dye solution. Moreover, our time-integrated fluorescence measurements revealed that no fluorescence emission could be detected. The application of ultrashort pulses of ∼40 fs duration enabled the tracking of ESPT in the Hibiscus dye, which was not detected in previous studies that employed laser pulses of picoseconds and nanoseconds duration.

Crystalline Phase Effects on the Nonlinear Optical Response of MoS2 and WS2 Nanosheets: Implications for Photonic and Optoelectronic Applications

In the present work, some MoS2 and WS2 nanosheets were prepared and characterized. Depending on the preparation procedures, trigonal prismatic (2H) or octahedral (1T) coordination of the metal atoms was obtained, exhibiting metallic (1T) or semiconducting (2H) character. Both MoS2 and WS2 nanosheets were found exhibiting large nonlinear optical (NLO) responses, strongly dependent on their metallic (1T) or semiconducting (2H) character. Therefore, the semiconducting character of MoS2 and WS2 exhibits positive nonlinear absorption and strong self-focusing behavior, while their metallic character counterparts exhibit strong negative nonlinear absorption and important self-defocusing behavior. In addition, the semiconducting MoS2 and WS2 were found exhibiting important and very broadband optical limiting (OL) action extending from 450 to 1750 nm. Therefore, by selecting the crystalline phase of the nanosheets, that is, their semiconduction/metallic character, their NLO response can be greatly modulated. The results of the present work demonstrate unambiguously that the control of the crystalline phase of MoS2 and WS2 provides an efficient strategy for 2D nanostructures with custom-made NLO properties for specific optoelectronic and photonic applications such as OL, saturable absorption, and optical switching.

Gamma-radiation-induced negative nonlinear absorption in quartz glass

The effect of ionizing radiation on the nonlinear optical properties of materials needs to be considered for applications that employ high-power laser pulses in extreme radiation environments. The Heraeus Infrasil302 optical quartz glass was irradiated by gamma rays, and its nonlinear absorption was measured using the open-aperture Z-scan technique with nanosecond laser pulses. Irradiation results in a negative nonlinear absorption coefficient whose magnitude increases with irradiation dose. Nonlinear absorption coefficients of −0.78, −1.14, −1.29, and −1.88~ × ~10−13 m/W are measured for gamma doses of 600 krad, 1.2 Mrad, 3.6 Mrad, and 10 Mrad, respectively. Thermal annealing restores the optical properties of quartz-glass to their unirradiated values. It is suggested that metallic impurities introduced by the manufacturing process have a role in inducing saturated absorption in irradiated quartz glass, which manifests as negative nonlinear absorption coefficient, and is demonstrated by comparing Infrasil302 quartz results to equivalent irradiated measurements for Spectrosil2000 quartz.

Low-order optical nonlinearities of PbS quantum dot liquids and films

We demonstrate the variations of the nonlinear optical parameters in the suspensions and thin films containing PbS quantum dots of different sizes (9 and 2.5 nm). We show that these colloidal quantum dots possess the thermal-lens induced negative nonlinear refraction and reverse saturable absorption in the case of the 532-nm, 10-ns probe pulses. The larger nonlinear absorption coefficients of 9-nm quantum dots compared with 2.5-nm species (1 × 10−7 and 8 × 10−9 cm W−1, respectively) in the case of 1064 nm, 10 ns probe pulses were determined. Similar relations between the nonlinear optical parameters of 9- and 2.5-nm species were maintained in the case of twice shorter wavelength (532 nm) of the probe pulses. The almost ten-fold growth of the nonlinear optical parameters in the visible range compared with the near infrared region was attributed to the stronger influence of the excitonic states on the propagation effects in the former case. We show that the thin films containing these quantum dots demonstrate saturable absorption, while the suspensions show mostly the reverse saturable absorption at 532 nm. A significant enhancement of the nonlinear refractive index of films compared with suspensions (−2 × 10−8 cm2 W−1 and -1 × 10−11 cm2 W−1), as well as a large negative nonlinear absorption coefficient (−3.2 × 10−5 cm W−1) in the former case are demonstrated. We discuss the signs of nonlinear refraction and nonlinear absorption of the quantum dots, as well as the role of the sizes of these species in variations of the nonlinear parameters.

Effect of Solvent on Third-Order Nonlinear Optical Behavior of Reactive Blue 19 Dye.

The present work focuses the study of effectof solvent on third-order nonlinear optical (NLO) properties of reactive blue 19 dye dissolved in various polar solvents, namely ethanol, DMF and DMSO, respectively. Fourier Transform Infrared Spectroscopy (FT-IR) was used to find the functional groups present in reactive blue 19 dye. Third-order NLO features of reactive blue 19 dye was examined by a low power continuous wave laser of 650nm wavelength. Reactive blue 19 dye exhibit negative nonlinear index of refraction of the power of 10-7 cm2/W and the nonlinear coefficient of absorption of the order of 10-3cm/W. Both positive and negative nonlinear absorption coefficient of reactive blue 19 dye in different polar solvents is due to the characteristic behavior of saturable and reverse saturable absorption. Third-order NLO susceptibility of reactive blue 19 dye in polar solvents was determined to be the power of 10-6 esu. The experimental results reveal that the dye samplereactive blue 19 is a potential material for nonlinear optical applications.

Photoluminescence characterizations and nonlinear optical of PM-355 nuclear track detector film by alpha-particles and laser irradiation

The imaging processing technique was used for studying a laser beam nature that transmitted through films of PM-355. The thermal nonlinearity of PM-355 films was studied using a 635 nm cw diode laser at 15 mW as the source of excitation. Third order nonlinear optical properties of PM-355 films irradiated with α-particles at different times and pristine sample has been studied using Z-scan technique. The samples showed a negative and large nonlinear refractive index and reverse saturable absorption (RSA) with high values of the nonlinear absorption coefficient. The fluorescence spectra of PM-355 films were investigated at room temperature and wavelength range of 250–500 nm for a pristine film and in different times of exposure to α-particles. The broad peaks were between 350, 420 and 465 nm. All-optical switching property of PM-355 samples irradiated with α-particles at 20 min was also studied using the standard pump-probe technique.

Tuning the nonlinear optical properties of Au@Ag bimetallic nanoparticles

In this work, we report the nonlinear optical properties of Au@Ag bimetallic nanoparticles synthesized by a seed-mediated method. For the synthesis of bimetallic nanoparticles, gold seeds with particle size of 18 nm were synthesized by citrate assisted thermal reduction method, followed by the reduction of silver ions with ascorbic acid. The nanoparticles were characterized by means of UV–Vis spectrophotometry, SEM and Z-scan measurements with an Argon CW laser of variable power at 514 nm was used to determine the nonlinear optical properties. Au@Ag core-shell nanoparticles presents negative and positive nonlinear absorption coefficient and the nonlinear refraction index is negative. Moreover, the results show that the nonlinear optical properties can be tailor modifying the thickness of shell.

Linear and nonlinear optical properties of chlorophyll-a extracted from Andrographis paniculata leaves

This paper reports the linear and third-order nonlinear optical (NLO) properties of chlorophyll-a, a natural pigment extracted from the medicinal plant Andrographis paniculata. Silica column chromatography technique was used to extract the chlorophyll-a from the plant leaves. The functional groups present in the extracted sample were recognized by Fourier transform infrared (FT-IR) spectra. The sample was also characterized by UV–Vis, fluorescent spectra and Z–scan techniques. Z–scan study reveals that the extracted natural pigment chlorophyll-a evinces a large negative nonlinear refractive index n2 and nonlinear absorption coefficient β respectively owing to self-defocusing and saturable absorption behaviors. Third-order NLO susceptibility χ(3) of chlorophyll-a was measured to be of the order of 10–6 esu. The sample fulfilled the conditions for figure of merit and we believe that the natural pigments extracted from the Andrographis paniculata leaves may be suitable for all-optical switching applications.

Study of nonlinear properties of N-(2-hydroxyphenyl)-2-propylpentanamide in polymeric solution

We have studied the nonlinear optical properties for synthesized materials by using the Z-scan technique, in order to measure nonlinear refractive indices. The nonlinear optical properties of synthesized N-(2-hydroxyphenyl)-2-propylpentanamide (HO-AAVPA), in micellar aqueous solution of F127, were properly studied by using the technique explained above. Additionally, the optical transmittance signal was obtained with and without finite aperture using a 26 ps Nd:YAG pulsed-laser, at 532 nm and featuring a 10 Hz repetition rate. The solution shows a high NLO response at the wavelength studied. The positive nonlinear refraction index and negative nonlinear absorption coefficient were experimentally obtained for the sample under test. Finally, atomic force microscopy (AFM) images were used to analyze the topography of these samples. It was demonstrated that adding the hydrophobic HO-AAVPA molecule to the F127 solution, the surface topography abruptly changes forming a kind of spherical structures. In addition, the linear absorption spectrum was obtained for the HO-AAVPA with and without F127.

Large Stokes Shifted Far‐Red to NIR‐Emitting D‐π‐A Coumarins: Combined Synthesis, Experimental, and Computational Investigation of Spectroscopic and Non‐Linear Optical Properties

AbstractCoumarin based push‐pull fluorophores (COM‐1 to COM‐5) bearing thiophene π‐spacer were synthesized having a donor at 7‐position and acceptor at 3‐position. Increasing the π‐conjugation length shifts their fluorescence maxima to the longer wavelength (600–756 nm). All fluorophores exhibit positive emission solvatochromism, fluorescence lifetime is in the range of 1.31 to 2.18 ns, and are high thermal stability. The nonlinear optical behavior was investigated by calculating the first/second‐order hyperpolarizability using a spectroscopic and computational method wherein, COM‐3 shows higher optical nonlinearity (μβCT=987 x 10−48 e.s.u and μβ0=9758 x 10−48 e.s.u.) in DMF. Third‐order nonlinear optical parameters measured using the Z‐scan method in each closed and open aperture curves. The fluorophores possess the self‐focusing effect and show negative nonlinear absorption coefficient (β) and positive nonlinear refractive index (n). Among all fluorophores, COM‐5 shows better real part of third‐order susceptibility χ(3) in DMSO (8.58 x 10−13 e.s.u.). Bond length alternation (BLA), natural bond orbital analysis (NBO), and generalized Mulliken‐Hush (GMH) analysis were studied to give theoretical evidence to the effective charge transfer (CT). Quadratic optical nonlinearity and Z‐scan results show that these coumarin‐based fluorophores can be considered as promising candidates for organic NLOphores in material for nonlinear optics.

Intensity dependent refraction and absorption in doped graphene by perturbation theory

The previous studies on graphene were primarily focused on the effect of photon energy to optical nonlinearities but less on that of doping. By the perturbative treatment of external field, we theoretically illustrate the dependence of the second order refractive and absorptive indices on the Fermi energy of doped graphene with the effects of relaxation and temperature. Some new phenomena are observed. Due to thermal fluctuations at finite temperature, photon with energy below twice the Fermi energy could also induce nonlinearities as the ones above that. And when the Fermi energy is around half that of incident photon, giant enhancement of nonlinear refraction and negative nonlinear absorption could be obtained. We also find interband relaxation dominates in nonlinear decrements rather than intraband one. By comparison between the results of simulation with those of other experiments, the perturbation theory of optical nonlinearities of graphene is confirmed.

Photoresponsive behavior and switchable nonlinear optical properties of Langmuir-Blodgett film based on azobenzene derivatives.

Here, we present the investigations of photo-isomerization behavior and the nonlinear optical properties of azobenzene derivative LB films. The few-layer LB films of AOB-t4 and BNB-t4 exhibit positive nonlinear refraction and two-photon absorption properties as revealed by picosecond Z-scan. The increased conjugation by introducing an oxadiazole group improves the photo-isomerization rate and the nonlinear optical properties, due to a weaker intermolecular interaction and the formation of J-aggregates within AOB-t4 LB film. The third-order susceptibility of cis-AOB-t4 9-layer LB film reaches 1.866 × 10-9 esu and the two-photon absorption coefficient is on the order of 10-8 m/W. Interestingly, the 15-layer AOB-t4 LB film shows negative nonlinear refraction and saturable absorption. Taken together, we have demonstrated the switchable nonlinear optical absorption and refraction properties of AOB-t4 LB film with changing film thickness, which is of significance for nonlinear optics and photonics applications.

Laser induced optical and microscopic studies of salicylic acid influenced KH2PO4 crystal for photonic device applications

The present communication is aimed to explore the characteristic properties of salicylic acid (SA) doped potassium dihydrogen orthophosphate (KDOP) crystal. The single SA doped KDOP crystal with optimum dimension of 10 × 08 × 04 mm3 has been grown from solution by slow evaporation at ambient temperature. The single crystal X-ray diffraction analysis has been employed to determine the structure and cell parameters of grown crystal. The Z-scan studies have been carried out at 632.8 nm to ascertain the influential third-order non-linear optical (TONLO) nature of SA doped KDOP crystal. The Z-scan transmittance data have been used to determine the magnitude of TONLO susceptibility (χ3), absorption coefficient (β) and refractive index (n2) of SA doped KDOP crystal. For grown crystal, the surface damage due to exposure of high intensity of Nd:YAG laser operating at 1064 nm has been determined and found of order MW cm−2. The growth tendency, etch pattern and surface quality of grown SA doped KDOP crystal has been investigated by means of etching studies. The thermal response of grown crystal has been examined by differential thermal analysis employed in the range of 23–800°C. The hardness number of SA doped KDOP crystal has been investigated by means of Vickers microhardness study by applying different load ranging from 25 to 100 gm. The work hardening index and elastic stiffness coefficient have been evaluated using the hardness data. The nature of photoconductivity exhibited by grown crystal has been determined in voltage range of 10–100 V.Highlights• Z-scan analysis revealed negative non-linear refraction and reverse saturable absorption effect in SA-KDOP crystal.• The laser damage threshold of SA-KDOP crystal at 1064 nm is found to be 274·74 MWcm−2.• SA-KDOP crystal exhibited positive photoconducting nature within 10–100 V.• The dopant SA facilitated large enhancement in hardness parameters of KDOP crystal.• Etching and thermal analysis has been performed.

Influence of Ga doping ratio on the saturable absorption mechanism in Ga doped ZnO thin solid films processed by sol–gel spin coating technique

In the present study, the nonlinear optical properties of sol–gel spin coated gallium doped zinc oxide (GZO) thin solid films are explored with nanosecond laser pulses using the z-scan technique. The higher doping ratios of Ga result in a large redshift of the energy gap (0.38 eV) due to the existence of enhanced grain boundary defects in GZO films. A positive nonlinear absorption coefficient is observed in undoped 1 at.wt.% GZO and 2 at.wt.% GZO films, and a negative nonlinear absorption coefficient in 3 at.wt.% GZO film. Fewer defects in undoped 1% GZO and 2% GZO films resulted in reverse saturable absorption (RSA), whereas a saturable absorption (SA) mechanism is observed in 3% GZO films and is attributed to the enhanced defect concentration in the band structure of GZO. However, all the films showed a self-defocusing mechanism, derived by a closed aperture z-scan technique. The present work sheds light on the defect mechanism involved in the observed nonlinear properties of GZO films.

Physicochemical and Nonlinear Optical Properties of Novel Environmentally Benign Heterocyclic Azomethine Dyes: Experimental and Theoretical Studies.

Novel heterocyclic azomethine dyes were prepared by the reaction of anthracene-9-carbaldehyde with different heterocyclic amines under microwave irradiation. Structures of the azomethine dyes were confirmed by the elemental analysis, mass spectrometry and several spectroscopic techniques. We studied absorbance and fluorescence spectra of the azomethine dyes in various solvents. They are found to be good absorbers and emitters. We also report photophysical properties like, extinction coefficient, oscillator strength, stokes shift and transition dipole moment. This reflects physicochemical behaviors of synthesized dyes. In addition, their intramolecular charge transfer and nonlinear optical properties, supported by natural bond orbital technique, were also studied computationally by density functional theory. The negative nonlinear refractive index and nonlinear absorption coefficient were measured for these dyes using the closed and open aperture Z-scan technique with a continuous wave helium-neon laser. These are found to vary linearly with solution concentration.

Facile synthesis of tunable fluorescent carbon dots and their third-order nonlinear optical properties

We report the synthesis and luminescent properties of carbon dots whose peak fluorescence emission are independent of excitation wavelength. Meanwhile, varying the concentrations of carbon dots can achieve a shift in the emission wavelength. Detailed structural characterization and optical properties of carbon dots with different concentrations were studied. Particularly, the blue-shifted excitation-independent emission peaks were observed when the concentration of carbon dots decreased. The decreased fluorescent properties were considered to originate from the surface modification of carbon dots. Additionally, we investigated the third-order nonlinear optical responses of carbon dots with different concentrations by Z-scan technique with single 190 fs laser pulses at 532 nm. It was found that both samples exhibited positive nonlinear refractivity and negative nonlinear absorption coefficient in the fs regime. These tunable optical properties would provide more possibilities for the utility of carbon dots in optical devices.