Nonlinear Absorption Properties Research Articles

Revealing the Role of Electronic Effect to Modulate the Photophysics and Z-Scan Responses of o-Locked GFP Chromophores.

Three novel core green fluorescent protein (GFP) chromophore analogues, based on a doubly locked conformation and variable electronic effects by replacing one hydrogen with bromine, iodine, and methyl, respectively, have been synthesized to modulate the push-pull effect. These chromophores exhibited intramolecular H-bonding, as evidenced by single-crystal X-ray and 1H NMR studies. The fluorescence quantum yields (ϕf) of all of the chromophores were found to be more than an order of magnitude higher (∼0.2) than the unlocked chromophores (∼0.01). It was found that the electronic effect did affect the nonradiative rates, as the quantum yields were found to vary with respect to different analogues in the same solvents. The effect of the push-pull effect was also evident by a higher Stokes-shifted emission in the case of the methyl derivative with respect to the bromo- and iodo-analogues. Furthermore, the emission spectra of these GFP chromophores were found to show positive solvatochromism, which was supported by a quantum chemical calculation. A detailed study, correlating the observed spectral changes with various solvent functions and supported by computational results, established a facile proton transfer, followed by twisted intramolecular charge transfer (TICT) to be the major nonradiative channels of these chromophores. Besides, a completely novel usage of these chromophores was explored for the first time by studying their third-order nonlinear optical characteristics in DMSO using a single-beam Z-scan technique. All of the chromophores exhibited tunable nonlinear refraction (NLR) and nonlinear absorption (NLA) properties that depend upon different substituent groups present in the chromophores. Here, the NLR was due to the effect of self-defocusing, whereas the NLA was triggered by reverse saturable absorption, which is attributed to the two-photon absorption (TPA) process. Surprisingly, the efficiency of the TPA ability of the chromophores was found to be a function of the induced electronic effect. Hence, this work opens a new route for the utility of the ortho-locked GFP chromophores in the field of nonlinear optical applications.

Large-energy operation of an Er-doped fiber laser with ZrGeTe4 saturable absorber

ZrGeTe4 as a layered semiconductor material with good stability and optoelectronic properties, and excellent saturable absorption characteristics, but its application in fiber lasers is still insufficient. In order to explore its application in fiber lasers, we prepared ZrGeTe4-PVA thin film by liquid phase exfoliation and performed a series of characterizations. A modulation depth of 13.15 %, a non-saturated loss of 6.4 %, and a saturation intensity of 5.5 MW/cm2 were obtained. Then used the ZrGeTe4-PVA thin film as the saturable absorber (SA) in an Er-doped fiber laser (EDFL), the large-energy operation could be realized. In the case of a cavity length of 234 m, when the pump power was increased to 1229 mW, a maximum single pulse energy of about 32.72 nJ was achieved, with a repetition frequency of 859 kHz. To the best of our knowledge, this is the highest single-pulse energy achieved in an EDFL based on ZrGeTe4-SA. This experiment shows that the ZrGeTe4 is a promising two-dimensional (2D) material with good nonlinear absorption properties, proving that it is a promising pulse modulation of SA and laying a foundation for its subsequent study in fiber lasers.

Nonlinear absorption properties in gold nanoparticles for passively Q-switched laser and optical limiting applications

Nonlinear absorption properties in gold nanoparticles for passively Q-switched laser and optical limiting applications

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.

Utilization of Te as a saturable absorber for mode-locked 2.8 µm Er3+: ZBLAN fiber laser

In this manuscript, we present the experimental realization of a mode-locked Er3+: ZBLAN (ZrF2- BaF2- LaF3- AlF3- NaF) fiber laser operating at mid-infrared (mid-IR) 2.8 μm band, achieved through the utilization of Tellurium (Te) as the saturable absorber (SA). An exploration of their nonlinear optical absorption properties at 2.8 μm was undertaken employing a dual-channel detection methodology. Our investigation reveals that the Te-SA prepared exhibits a significant broadband saturable absorption response, thereby confirming its suitability as SA for passive mode-locked fiber laser at 2.8 μm. The peak average output power pulse and energy of the mode-locked Er3+: ZBLAN fiber laser are 41.2mW and 1.632nJ, respectively. These measurements were conducted at a repetition rate of 25.25 MHz, accompanied by a signal-to-noise ratio (SNR) of 60 dB at a transmit pump power of 600 mW. This is the first demonstration of a mode-locked fiber laser operating in the 2.8 µm mid infrared band using Te-SA.

Effect of morphology modulation and interface engineering of SnS-MoS2 heterojunction on nonlinear optical response

MoS2 base films with different morphologies were prepared by modulating the magnetron sputtering parameters, and the base films were used to induce the growth of SnS with different structures, forming columnar and worm-like SnS-MoS2 heterojunctions, which were found to have excellent nonlinear absorption properties and their properties could be modulated by the morphology of the films by Z-scanning tests. The tunable morphology and crystalline quality of the films were characterized using scanning electron microscopy, atomic force microscopy and X-ray diffraction techniques and explained using the Stranski-Krastanow growth mechanism. The Raman spectrum of the heterojunction shows the A1g vibrational peak at 320 cm−1 and the appearance of Sn4+ in the X-ray photoelectron spectroscopy confirms the existence of S-Sn-S charge transfer channels between the interfaces. The fine spectra of all the elements in the X-ray photoelectron spectroscopy data as well as the characteristic absorption peaks in the absorption spectra confirm the formation of heterojunctions, and the constructed heterojunctions are determined to be type-II heterojunctions using the method of the core energy level. Heterojunction was determined to be a type-II heterojunction by using the core energy level method. The photoluminescence peak quenching of the heterojunction indicates that there is a process of charge transfer between the interfaces, and the type-II heterostructure of SnS-MoS2 makes the nonlinear absorption performance in the 800 nm band regulated by the morphology of the material. The nonlinear optical absorption coefficient is two orders of magnitude higher than that of the pure materials, and the nonlinear absorption performance of the worm-like SnS-MoS2 heterojunction is superior to that of the columnar SnS-MoS2 heterojunction, which is attributed to the larger interfacial contact area, the better crystalline quality, and the more efficient carrier interfacial transport capability. These tunable type-II SnS-MoS2 heterojunctions with ultrafast nonlinear optical absorption have a positive impact on practical applications such as optical limiter devices and all-optical switching devices.

Few-layer NbTe2 nanosheets-based saturable absorber for generating 176 fs pulse at 1 μm in ultrafast fiber laser

Ultrafast fiber lasers play an increasingly vital role in diverse fields of science and industry. In this study, a novel NbTe2 nanosheet-based saturable absorber (SA) was prepared by using liquid phase exfoliation and flame brush technology for the first time. Using a twin balance measurement system, the nonlinear optical absorption property was checked. It was found that the fabricated NbTe2 nanosheets-based SA has excellent saturable absorption properties with a large modulation depth of 5.3 %, a very high saturation intensity of 1.11 GW/cm2, and a low non-saturation loss of 63.6 %. After inserting the NbTe2 nanosheets-based SA into a ring-cavity ytterbium-doped fiber laser (YDFL), a stable soliton mode-locking state was achieved. A 176-fs ultrafast soliton pulse train was successfully generated at 1029.76 nm with the repetition rater of 3.097 MHz. Thanks to the unique and very high saturation intensity of NbTe2 nanosheets, the proposed YDFL system achieved a maximum peak power of 96.3 kW and a single pulse energy of 14.09 nJ under 370 mW pump power. These findings indicate that NbTe2 nanosheets have great potential for generating ultra-short optical pulses with higher peak power in mode-locked fiber lasers.

Defect-controlled fabrication of reduced graphene oxide/ZnO/PMMA-based solid-state optical limiting filters with SA/RSA switching property

A solid-state optical limiting filter was fabricated by noncovalently functionalizing a graphene-based nanocomposite with a polymer. Graphene oxide was reduced by varying reducing agent concentration and functionalized with metal oxide nanoparticles to enhance electronic transitions and third-order nonlinear optical characteristics. The nanocomposite was dispersed over the PMMA polymer framework, and thin films with μm-scale thickness were fabricated using the dip coating method. XRD analysis confirmed the wurtzite crystal structure of ZnO nanoparticles and the amorphous nature of PMMA. The carbon structural integrity was analyzed using Raman spectra. Linear optical studies revealed a redshift in the π-π* transition peak in rGO, suggesting enhanced conjugation. Third-order nonlinear refraction and absorption properties were assessed using the Z-scan technique, revealing a switching behavior in nonlinear absorption at different input intensities. An increase in the relative concentration of sp2 domains enhanced the nonlinear absorption. Optical limiting potential, determined using open aperture Z-scan data, yielded a threshold value of 0.066 GW/cm2. This study aims to develop a solid-state optical filter with a high laser damage threshold by adjusting the reduction rate, tuning defect levels, and analyzing its effect on the optical limiting potential.

Watt‐Level Second‐Order Topological Charge Ultrafast Green Vortex Laser with Quasi ‐2D PEA2(CsPbBr3)n‐1PbBr4 Perovskite Films Saturable Absorber

AbstractUltrafast vortex beams have significant scientific and practical value because of their unique phase properties in both the longitudinal and transverse modes, enabling multi‐dimensional quantum control of light fields. Directly generating watt‐level ultrafast vortex beams with large angular momentum has remained a major challenge due to the limitations of mode‐locked materials and existing spatiotemporal mode‐locking generation methods. In this study, quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films are prepared by an anti‐solvent method and employed for the first time in a mode‐locked resonator operating in free space. Utilizing the angle‐based non‐collinear pumping and frequency doubling techniques, the second‐order ultrafast green vortex beams with a power of up to 1.05 W and a duration of 373 ps are generated. Experimental findings demonstrate the strong nonlinear saturable absorption properties of quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films at high power levels, highlighting their considerable potential in ultrafast laser technology and nonlinear optics.

Tailoring epsilon-near-zero wavelength and nonlinear absorption properties of CdO thin films by Mo doping

Cadmium oxide (CdO) has recently attracted attention as a material with controllable properties tailored for optoelectronic and nanophotonic devices due to its superior mobility. However, its potential application in near-infrared (NIR) remains to be explored. In this work, we demonstrate that the epsilon-near-zero (ENZ) wavelength and nonlinear optical properties of CdO films can be effectively tuned by Mo doping. The results show that Mo doping increases the electron concentration as well as improve the crystalline quality of CdO. With increasing Mo doping, we achieve blueshifts of the ENZ wavelength from 2.89 to 1.56 μm. The nonlinear absorption (NLA) behavior at 1550 nm changes from reverse saturable absorption to saturable absorption with increasing Mo content. Moreover, significant improvement in NLA performance with nonlinear absorption coefficient β = −72 cm/GW is observed at the highest doping content. Our work shows that doped CdO films with tunable optoelectrical and nonlinear optical properties can be an ideal candidate for optoelectronic and nanophotonic application in the NIR region.

Ultrafast laser pulses generation by using the ultrasmall topological semimetal TaN quantum dots

The synthesis of ultrasmall tantalum mononitride (TaN) quantum dots (QDs) is achieved using a straightforward liquid exfoliation technique, starting from bulk TaN. This work presents the evidence of generating an ultrafast laser by employing TaN QDs as a saturable absorber (SA) within an Erbium-doped fiber laser for the first time. Stable ultrashort pulses are generated, exhibiting a center wavelength of 1566.92 nm, a pulse duration of 713 fs, and a cavity repetition rate of 41.39 MHz. Furthermore, the utilization of TaN QDs as an SA in the device exhibits good nonlinear saturable absorption properties with a modulation depth of 1.37%. Those results presented in this study add to the existing literature on the investigation of nonlinear optical characteristics of ultrasmall QDs and also highlight the potential for future development in ultrafast photonic technology.

V2O5/Ti3C2 MXene-Based Solid-State Passively Mode-Locked Tm:YAP laser at 2 μm

In the present work, V2O5/Ti3C2 MXene hybrid nanomaterials were successfully synthesized. The morphology and structure of the prepared V2O5/Ti3C2 MXene were investigated, and the results showed excellent bonding and strong interaction between Ti3C2 MXene and V2O5 nanoparticles. The nonlinear absorption properties of V2O5/Ti3C2 MXene nanocomposites at 2 μm have been investigated using power transfer techniques, and the large modulation depth of the material gives it potential for applications in nonlinear optics. As a result, a 2 μm solid-state mode-locked pulsed laser with V2O5/Ti3C2 MXene as a saturable absorber has been realized for the first time, generating a pulsed laser output as short as 657 ps, which corresponds to an average output power of 0.67 W. The results show that the synthesized V2O5/Ti3C2 MXene hybrid nanomaterials, which have a large optical nonlinearity, can be applied to generating an ultrashort 2 μm pulsed laser.

Nonlinear Optical Saturable Absorption Properties of 2D VP Nanosheets and Application as SA in a Passively Q-Switched Nd:YVO4 Laser.

Two-dimensional (2D) violet phosphorus (VP) plays a significant role in the applications of photonic and optoelectronic devices due to its unique optical and electrical properties. The ultrafast carrier dynamics and nonlinear optical absorption properties were systematically investigated here. The intra- and inter-band ultrafast relaxation times of 2D VP nanosheets were measured to be ~6.83 ps and ~62.91 ps using the pump-probe method with a probe laser operating at 1.03 μm. The nonlinear absorption coefficient βeff, the saturation intensity Is, the modulation depth ΔR, and the nonsaturable loss were determined to be -2.18 × 104 cm/MW, 329 kW/cm2, 6.3%, and 9.8%, respectively, by using the Z-scan and I-scan methods, indicating the tremendous saturable absorption property of 2D VP nanosheets. Furthermore, the passively Q-switched Nd:YVO4 laser was realized with the 2D VP nanosheet-based SA, in which the average output power of 700 mW and the pulse duration of 478 ns were obtained. These results effectively reveal the nonlinear optical absorption characteristics of VP nanosheets, demonstrating their outstanding light-manipulating capabilities and providing a basis for the applications of ultrafast optical devices. Our results verify the excellent saturable absorption properties of 2D VP, paving the way for its applications in pulsed laser generation.

Two-photon absorption in quantum dots with Hellmann potential

Abstract We study the nonlinear optical absorption properties of a spherical quantum dot (SQD) with Hellmann potential, focusing on the two-photon absorption (TPA) process, using GaAs/AlGaAs material as an example. The radial Schrödinger equation is solved using the Nikiforov-Uvarov method, while the two-photon absorption coefficient is determined through second-order perturbation theory concerning the electron-photon interaction. Our study shows that the intraband transition has a smaller energy transition than the interband transition, leading to TPA spectra for the intraband transition that is restricted within a smaller energy range and exhibits a higher peak value than those for the interband transition. The peak corresponding to the orbital quantum number of electrons in SQD ℓ = 2 consistently appears to the left of the peak corresponding to ℓ = 1 in both intraband and interband transition cases. Additionally, the dependence of the absorption peak position on the order of transition, n, differs between intra- and inter-band transitions. We also observe blue shift behavior in the TPA spectra as all three parameters, r 0, V 0e , and η, increase. Our investigation has the potential to enable the design of novel photonic devices, ultra-fast optical switches, and highly efficient solar cells through the optimization of quantum dot material properties.

Comprehensive study on the nonlinear optical properties of Ag/MoSe2 composite films

MoSe2 thin films and Ag/MoSe2 composite thin films were prepared by physical vapour deposition (PVD). The morphology and structure of the composite film were characterized by scanning electron microscopy and absorption spectroscopy. The UV–visible absorption spectrum characterizes the linear absorptivity of the composite films. Due to the plasma effect of Ag nanofilms, the Ag/MoSe2 composite films showed a significant increase in the absorption intensity of the films compared to the MoSe2 films. The nonlinear absorption properties of MoSe2 thin films were investigated using the open-aperture Z-scan technique. The calculated nonlinear absorption coefficient (β) showed that the nonlinear absorption coefficient of the Ag/MoSe2 composite film is an order of magnitude higher than that of the MoSe2 film, indicating that the Ag nanofilm can better improve the nonlinear absorption properties of the MoSe2 film.

2D Ti4AlN3 (MAX): An excellent infrared nonlinear absorption material

Two-dimensional (2D) materials have drawn more attention since the discovery of graphene. The exploration of the nonlinear optical (NLO) properties of 2D materials has become more urgent. In this work, Ti4AlN3 nanosheets with a thickness of about 1.7–1.9 nm were prepared using the liquid phase exfoliation (LPE) method, and the open aperture (OA) Z-scan technique was used to explore the broadband nonlinear absorption (NLA) properties of 2D Ti4AlN3 nanosheets at three wavelengths, namely, 355, 532, and 1064 nm. According to the results, 2D Ti4AlN3 nanosheets exhibited excellent optical limiting (OL) behavior in all three bands, especially in the infrared (IR) band. The large two-photon absorption (TPA) coefficient and low OL excitation threshold indicated that Ti4AlN3 had great potential as OL material in the IR band for applications such as optical filters, protection of the human eye, laser protection, etc.

Revealing photoluminescence and nonlinear optical absorption characteristics of PbMo0.75W0.25O4 single crystal for optical limiting applications

Nonlinear absorption properties of PbMo0.75W0.25O4 single crystal fabricated by the Czochralski method were studied. The band gap energy of the crystal was determined as 3.12 eV. Urbach energy which represents the defect states inside the band gap was found to be 0.106 eV. PbMo0.75W0.25O4 single crystal has a broad photoluminescence emission band between 376 and 700 nm, with the highest emission intensity occurring at 486 nm and the lowest intensity peak at 547 nm, depending on the defect states. Femtosecond transient absorption measurements reveal that the lifetime of localized defect states is found to be higher than the 4 ns pulse duration. Open aperture (OA) Z-scan results demonstrate that the PbMo0.75W0.25O4 single crystal exhibits nonlinear absorption (NA) that includes two-photon absorption (TPA) as the dominant mechanism at the 532 nm excitations corresponding to 2.32 eV energy. NA coefficient (β eff ) increased from 7.24 × 10−10 m W−1 to 8.81 × 10−10 m W−1 with increasing pump intensity. At higher intensities β eff tends to decrease with intensity increase. This decrease is an indication that saturable absorption (SA) occurred along with the TPA, called saturation of TPA. The lifetime of the defect states was measured by femtosecond transient absorption spectroscopy. Saturable absorption behavior was observed due to the long lifetime of the localized defect states. Closed aperture (CA) Z-scan trace shows the sign of a nonlinear refractive index. The optical limiting threshold of PbMo0.75W0.25O4 single crystal at the lowest intensity was determined as 3.45 mJ/cm2. Results show that the PbMo0.75W0.25O4 single crystal can be a suitable semiconductor material for optical limiting applications in the visible region.

Stress and interfacial/surface synergistically modulated charge transfer mechanism and nonlinear absorption properties in Ti3C2(-O)/MoS2 heterostructure

Here, Ti3C2(-O)/MoS2 with two interface contacts were obtained by two-steps of hydrothermal (HT)/HT and HT/magnetron sputtering (MS) technique. The visualizing orientation-controlled interlayer interconnection and vertical/lateral contact modes for interface properties and light-matter coupling effect have been analyzed. The Raman spectra of Ti3C2(-O)/MoS2(HT) verified that the redshift of characteristic peak for Ti3C2(-O) was dominated by interfacial stress. The results of Ti3C2(-O)/MoS2(MS) revealed that the overall blue shift of the characteristic peak for Ti3C2(-O) and the redshift of the characteristic peak for MoS2 can be attributed to the interface charge transfer of MoS2 to Ti3C2(-O). The exciton quenching of Ti3C2(-O) and the enhancement of the C exciton transition luminescence for MoS2 were observed in the photoluminescence result. It is proved that the high-excited electrons of Ti3C2(-O) transfers to the vibration level of the conduction band of MoS2 under photoexcitation. The nonlinear absorption and transient absorption properties of Ti3C2(-O)/MoS2 heterojunction were studied by Z-scan and pump–probe technology. An additional interfacial charge transfer signal in the hybrid spectra represents the efficient interfacial charge transfer of Ti3C2(-O)/MoS2(HT) and Ti3C2(-O)/MoS2(MS). This work also provides a basic theory for the emerging heterojunctions, which is conducive to developing the potential optoelectronic devices in energy environment field.

Saturable absorption properties and ultrafast photonics applications of HfS3.

In this Letter, we focus on investigating the ultrafast photonics applications of two-layer HfS3 nanosheets. We prepared two-layer HfS3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS3-based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS3 material. Furthermore, we utilized the two-layer HfS3 materials as SAs in an erbium-doped fiber cavity to generate mode-locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two-layer HfS3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS3 materials and highlights their potential for advanced optoelectronic devices.

Introducing Optical Nonlinearity in PDMS Using Organic Solvent Swelling

The feasibility of introducing optical nonlinearity in poly-dimethyl siloxane (PDMS) using organic solvent swelling was investigated. The third-order nonlinear refraction and absorption properties of the individual materials, as well as the PDMS/solvent compounds after swelling were characterized. The well-established Z-scan technique served as characterization method for the nonlinear properties under picosecond pulsed laser excitation at a 532 nm wavelength. These experiments included investigations on the organic solvents nitrobenzene, 2,6-lutidine, and toluene, which showed inherent optical nonlinearity. We showed that nitrobenzene, one of the most well-known nonlinear optical materials, has proven suboptimal in this context due to its limited swelling effect in PDMS and comparatively high (non)linear absorption, resulting in undesirable thermal effects and potential photo-induced damage in the composite material. Toluene and 2,6-lutidine not only exhibited lower absorption compared to nitrobenzene but also show a more pronounced swelling effect in PDMS. The incorporation of toluene caused a weight change of up to 116% of PDMS, resulting in substantial nonlinear optical effects, reflected in the nonlinear refractive index of the PDMS/toluene composite n2=3.1×10−15 cm2/W.