Ti-sapphire Femtosecond Laser Research Articles

Growth, structural, optical, thermal and terahertz time-domain spectroscopy of l-alanine single crystal: A potential amino acid based nonlinear optical material

In our present work, we focused on the terahertz (THz) based characterization of a very efficient organic nonlinear optical (NLO) single crystal of l-alanine (LA). Using the well-known slow evaporation solution growth method (SEST), an optically transparent amino acid-based LA crystal was effectively grown at room temperature. The structural information of the titled crystal was analyzed using powder X-ray diffraction (PXRD) which confirms the space group P212121 and orthorhombic structure of the crystal. Chemical etching of an as-grown single crystal was analyzed to identify the growth patterns. Fourier transform infrared (FTIR) and FT-Raman spectrometry were used to figure out the major functional groups that were present in the ingot crystal. The optical behaviour of LA crystal was observed through UV–Vis and Photoluminescence (PL) spectroscopies. The single crystal was found to have high transmission values over a wide range of wavelength. The PL results revealed that the main emission happens at 474 nm. Thermal stability of the titled compound was acquired by thermo-gravimetric and the differential thermo-gravimetric (TG-DTG) analysis. Open and closed aperture Z-scan measurements were used to analyze the third order nonlinear behavior of the as-grown sample using a femtosecond Ti-sapphire laser. To analyze the absorption peaks behavior Terahertz time-domain spectroscopy (THz-TDS) was also performed in the range 0.2–2.0 THz. The above study shows variation in absorption coefficient and refractive index at THz frequencies.

Single-sized N-functionality graphene quantum dot in tunable dual-modality near infrared–I/II illumination detection and photodynamic therapy under multiphoton nonlinear excitation

Doping sorted graphene quantum dots (GQDs) with heteroatoms and functionalizing them with amino acid could improve their radiative recombination and two-photon properties—including their excitation-wavelength-independent photoluminescence from the ultraviolet to the near-infrared-I (NIR-I) region, absorption, quantum yield, absolute cross section, lifetime, and radiative-to-nonradiative decay ratio—under two-photon excitation (TPE) at a low excitation energy and short photoexcitation duration, as determined using a self-made optical microscopy system with a femtosecond Ti–sapphire laser. Four types of sorted GQDs were investigated: undoped GQDs, nitrogen-doped GQDs (N-GQDs), amino-functionalized GQDs (amino-GQDs), and N-doped and amino-functionalized GQDs (amino-N-GQDs). Among them, the sorted amino-N-GQDs are effective as a two-photon photosensitizer and generate the highest quantity of reactive oxygen species for the elimination of multidrug-resistant cancer cells through two-photon photodynamic therapy (PDT). Larger amino-N-GQDs result in a greater number of C–N and N–functionalities, leading to a superior photochemical effect and more favorable intrinsic luminescence properties, making the dots effective contrast agents for tracking and localizing cancer cells during in-depth bioimaging in a three-dimensional biological environment under TPE in the NIR-II region. Overall, this study highlights the potential of large amino-N-GQDs as a material for future application to dual-modality two-photon PDT and biomedical imaging.

Investigation on the synthesis, growth, thermal and optical behavior of creatininium borate single crystal: A potential candidate for nonlinear optical applications

In the this study, we focus on the growth of a metal-organic creatininium borate (CRB) single crystal for third-order nonlinear optical (NLO) applications. Optically transparent & wide optical band gap single crystals of CRB were successfully harvested by adopting a slow evaporation solution technique (SEST) at a constant 40[Formula: see text]C temperature. The structural identification and lattice parameters of the grown sample were determined by powder X-ray diffraction (PXRD) using Rietveld analysis by FullProf Suite software. The occurrence of vacancy/interstitial defects produced during growth was investigated by high-resolution X-ray diffraction (HRXRD) using omega scan arrangement. A single peak with lower full width half maxima (56.4 arc s) was obtained from the scan which suggests that there were no grain boundaries for the grown crystal. Surface morphology and its features such as concentration of dislocations and defect sites on the as-grown sample were scrutinized using the etching technique. The optical band gap and UV–vis cut-off were examined and found to be 5.39 eV and 230 nm, respectively. Photoluminescence characteristics of the crystal show an emission at 377 nm upon excitation with a wavelength of 336 nm. The presence of radiative and non-radiative transitions inside the crystal due to excitation upon 266 nm laser was identified using time-resolved photoluminescence. Thermal stability and decomposition temperature of the compound were obtained by thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The third-order nonlinearity of the crystal was determined by Z-scan measurement technique with a femtosecond Ti-sapphire laser.

Graphene quantum dot composite with multiphoton excitation as near infrared-II probe in bioimaging

Non-radiative traps and structures are present on the graphene quantum dots doped with nitrogen and functionalized with amino groups (amino-N-GQDs) and multiple crystalline layers because of cross-link-enhanced emission. Secondary and tertiary amines, which are potential fluorophores, have also been observed on the polyethylenimine (PEI) coating of amino-N-GQDs. Cross-linked PEI coating reduced rotation and vibration, thereby enhancing the photoluminescence quantum yield (PL QY). Introduced nitrogen atoms from N dopants, amino-functionalized groups and PEI, as well as sulfur from polystyrene sulfonate (PSS) enhanced the cooperative effect on the properties of heteroatom-doped materials among electrons captured by new surface states. This enhanced radiative recombination and subsequently enhanced PL QY, therefore, surface conjugation improved the amino-N-GQD surfaces by increasing the quantum confinement of their emissive energy, evidenced by the increased PL QY of amino-N-GQD-PSS-PEI (or amino-N-GQD-polymer composites). In some situations, the maximum available power required for delivery to the two-photon imaging plane without damaging tissues limits imaging depth but the additional brightness provided by amino-N-GQD-polymer composites in this study extended the maximum imaging depth to 240 μm. Amino-N-GQD-polymer composites had favorable two-photon properties under two-photon excitation (self-developed femtosecond Ti–sapphire laser optical system; power: 23.93 nJ pixel−1, 160 scans, approximately 1.09 s of total exposure time; excitation wavelength: 980 nm, near-infrared-II region), indicating that cells treated with amino-N-GQD-polymer composites and the anti-epidermal growth factor receptor antibody can achieve two-photon luminescence with 1/81 of the power required for similar-intensity two-photon autofluorescence (1938.33 nJ pixel−1 with 800 scans, total exposure time of ∼5.44 s). The materials can serve as contrast agents for the non-invasive detection of biological specimens and interior tissues using a two-photon excitation wavelength in the near-infrared region.

In situ thermal characterisation and filamentary modification in Polymethylpentene

Polymethylpentene (PMP) polymers can be used to make advanced optics, especially for midinfrared (MIR) ultrafast optics. In this study, an optical parametric converter pumped by a Ti sapphire femtosecond laser was used to investigate the polymer. The thermal effect generated by loosely focused femtosecond near mid-infrared (MIR) pulses in bulky materials is observed in real-time, and the polymer exhibits thermal stability and conformability. To avoid strong linear absorption and to increase the nonlinear damage threshold, the spectral region for ultrafast applications is 1310 nm (0.95 eV)–1350 nm (0.92 eV). For the process in region VI, there is a sign of stronger coupling for short-wavelength photons, and the pulse duration is recommended to be lower than 160 fs. In the ultraviolet (UV) region, filamentary writing using a low-focused beam, the laser peak power was selected in the range of 2.2 MW–9.2 MW. High-density bulky gratings were written. The refractive-index modulation was significant, and the polymer exhibited highly nonlinear features. This study provides insights into the applications and production of PMP polymers in laser optics and laser engineering.

Effect of shock wave on optical properties of Propyl p-hydroxybenzoate single crystal: A self-defocusing third order nonlinear optical material

This work focuses on the effect of shock wave on optical properties of propyl p-hydroxybenzoate single crystal. An optically transparent single crystal was grown by adopting slow evaporation solution growth technique (SEST). Its structure was confirmed by powder X-ray diffraction using Reitveld refinement. The Hirshfeld surface morphology and the intermolecular interaction of titled compound was scrutinized using crystal explorer. Three shock waves generated at constant air compressor pressure of 0.78 Mpa with calculated Mach number 1.7 were allowed to interact with the grown crystal. The UV–vis spectroscopy analysis on shock wave treated sample shows an increase in transmittance for 1st and 2nd shock and a reduction of transmittance for the 3rd shock wave. The defects induced after each shockwave – sample interaction was investigated by photoluminescence spectroscopy and surface morphology studies in detail. The third order nonlinear properties like self – defocusing and reverse saturation absorption of grown crystal were studied using a femto-second Ti-sapphire laser source. The nonlinear absorption coefficient, refractive index were calculated to be 4.04 ˟ 10−10 cm/W and −8.47 ˟ 10−15 cm2/W using open and closed aperture Z-scan measurement respectively.

Copper-based thiospinel quantum dots as potential candidates for nonlinear optical applications

Development of new materials such as CuNiCoS4, CuCo5S8, CuCo2S4 are some important candidates which have potential nonlinear optical applications in photonics such as multiphoton spectroscopy/microscopy, laser technology etc. In this study, ternary and quaternary structured group members CuNiCoS4, CuCo5S8, CuCo2S4 quantum dots (QDs) were synthesized experimentally using hot-injection method and investigated theoretically. The theoretical investigations based on Density Functional Theory (DFT) were revealed the electronic and lattice dynamical properties of these materials. The electronic band gaps obtained with DFT calculations were consistent with the band gaps that were obtained from the optical measurements. Nonlinear optical properties of CuNiCoS4, CuCo5S8 and CuCo2S4 in same molarities were examined using femtosecond z-scan method using the laser beam at 800 nm wavelength with different laser intensities. Two photon absorption coefficients and nonlinear refractive indexes were calculated about 10-11 cm/W and 10-16 cm2/W, respectively. Ti-Sapphire femtosecond laser z-scan was also employed to determine the third order nonlinear optical susceptibilities (χ (3)) of each sample and as a result; χ(3) of QDs was found about 10-10 esu.

Investigation on synthesis, structural and nonlinear optical responses of cadmium selenide coated with gold nanoparticles induced by femtosecond laser excitation

Nonlinear optical signal enhancement cannot be achieved by using semiconductor materials alone. Here, we show that the recently discovered nonlinear optical behavior of plasmonic nanoparticles and hybrid nanowires enables an enhanced nonlinear optical response. A synthesis, characterization, and nonlinear optical response of synthesized hybrid nanowires structures were studied. The growth of gold nanoparticles (Au NPs) onto cadmium selenide nanowires CdSe NWs with different concentrations of gold nanoparticles coating prepared via an impregnation technique. Au nanoparticles in the CdSe/Au nanowires were uniformly dispersed on the CdSe nanowire surface. The surface morphologies and the propagation manner of hybrid nanostructures were used for transmission electron microscopy (TEM) to study the optical properties of pure and hybrid nanostructures. Dark-field scattering microscopy was used to characterize single CdSe NW and confirm the coating of hybrid CdSe/Au nanowires and characterize the concentration effect of gold nanoparticles. The dark-field scattering spectrum (DFSS) reference to the surface plasmon resonance of nearer Au NPs was observed at ca. 800 nm. By making a comparison between a single cadmium selenide with and without gold nanoparticles coating, hybrid CdSe/Au nanowires exhibit sufficient quality to produce second-harmonic generation stimulated with a pulsed, linearly polarized pump-light from a femtosecond Ti-sapphire laser. The estimated improvement of the second-harmonic generation signal is about ~ 1.8 times, ~ 5.5 times, ~ 6.9 times for low, moderate and full coating of gold nanoparticles, which was mainly due to the high quality of synthesis techniques and good dispersion of gold nanoparticles on CdSe nanowires

Spectral-angular patterns and energy threshold for linear-to-nonlinear femtosecond laser pulse focusing in air

Focused propagation of a high-power ultrashort laser pulse is strongly influenced by optical medium nonlinearity that can significantly affect pulse parameters in the focusing region as compared to the linear focusing regime. We present the results of our experimental study and numerical simulations of frequency-angular patterns and laser plasma distribution of a gigawatt-power femtosecond Ti-sapphire laser pulse propagating in air under various focusing conditions. For the first time to the best of our knowledge, we found experimentally and confirm theoretically the range of pulse numerical aperture (NA), from approximately NA = 2 ⋅ 10−3 to 5 ⋅ 10−3, when both frequency and angular spectra broadening during supercritical laser pulse focusing in air is minimal. We attribute this NA-range to the transition region between quasilinear and nonlinear pulse focusing regimes. Additionally, the energy threshold for different pulse focusing regimes in the wide range of focusing conditions is obtained for the first time through the numerical simulations. This threshold is demonstrated to decrease with pulse NA increase.

Amelanotic B16-F10 Melanoma Compatible with Advanced Three-Dimensional Imaging Modalities

Amelanotic B16-F10 Melanoma Compatible with Advanced Three-Dimensional Imaging Modalities

Measurement of Energy Distribution of Output Electrons From a Microchannel Plate Based on Vacuum Photodiode

The energy distribution of output electrons (EDOE) from a microchannel plate (MCP) is measured using electrons emitted by a vacuum photodiode excited by a 266 nm Ti-sapphire femtosecond laser. The photoelectrons emitted from the photocathode are focused on a specific location of the MCP by a magnetic lens. While exist an enough voltage difference between the two ends of MCP, the energy distribution curve of output electrons form MCP can be obtained by analyzing the data as function of the bias voltage applied to the charge collector. The result shows that the energy distribution curve obtained by this means consists of a sharp and a long tail when using pulse light source. The most probable electron energy (MPE) is 12.64 eV and the full width at half maximum (FWHM) of the energy distribution curve is about 29.23 eV while the applied voltage difference is 700 V in the experimental setup. The MPE is 10.63 eV and the FWHM of the energy distribution is 22.436 eV in simulation. The measured curve is consistent with the expectation from simulation.

Fabrication, Characterization and Analysis of Concentrically Strained Silicon Nanowires With Extremely-High Hole Mobility

The findings from the time-of-flight (TOF) experiment for strained silicon nanowires are reported in this article, in combination with numerical simulations demonstrating new physical features involved in the quasi-quantum regime. The drift velocity of valence holes is demonstrated to exceed greatly that of conduction electrons. These experimental data are accurately reproduced by our simulations, revealing a dramatic reduction in the hole's effective mass as well as a significant extension of the mean-free time between two consecutive random scattering events due to combined effects of both quantum confinement and biaxial strain. Many-body theory is further introduced for calculating elastic-scattering rate of impurities with the inclusion of static screening under the random-phase approximation. Dark current, photo-current and photoluminescence spectra are all measured in our experiments, in addition to direct TOF experiment by employing a Ti-sapphire mode-locked femtosecond laser, and their data are fully analyzed and physically explained by using both simulations and many-body theory. Our observation that the Einstein's relation does not hold true for 1-D transport under a strong electric field is supported by a quantum-statistical calculation. Our discovery with a very large hole mobility is expected to play a key role in establishing a much more straight-forward technical path towards high-performance CMOS and radio-frequency amplifiers than current ones.

The Study on Tuning Photoluminescence of Colloidal Graphene Quantum Dots Synthesized through Laser Ablation

We report photoluminescence study of Colloidal Graphene Quantum Dots (GQDs) that synthesized from ablation of rGO solution. The rGO solution was ablated using 800 nm Ti-Sapphire femtosecond laser by varying the synthesize parameters such as laser power and ablation time. We observed that changing laser power 1 Watt to become 1.7 Watt and time ablation 20 minutes to become 60 minuteswill alterate the Photoluminescence (PL) curve peak of GQDs. In case of ablation power variation, PL data shows that the PL curve peak excited by 280 nm laser changed from 369.09 nm to 371.02 nm, and when it excited by 290 nm the PL curve peak slightly changed from 388.17 nm to 393.8 nm. The alteration of Photoluminescence peak is also observed in the variation of time ablation experiment, The PL curve peaks from GQDs time ablation variation samples excited by 280 nm were slightly changed from 376.81 nm to 373.59 nm, and when it excited by 290 nm laser, the PL curve peak is 391.55 nm then changed to 392.11. The change of PL peak on laser power or time ablation variation shows that both parameters will alter either the size, shape, or the edge-type of GQDs.

The Role of Reduced Graphene Oxide Concentration as Ablated Material on Optical Properties of Graphene Quantum Dots

We report the synthesize of Graphene Quantum Dots (GQDs) using ablation method with reduced Graphene Oxide (rGO) solution as a starting material. We have varied the concentration of rGO as following: 0.5, 2, 5 mg/ml and then have ablated them using 800 nm Ti-Sapphire femtosecond laser to obtain GQDs. From the UV-Vis data, we observed that the more concentration of rGO is being ablated, the more secondary absorption peak at 255.1 nm appeared. This secondary absorption peak is a characteristic of n-π* bonding due to the presence of oxygen defect which occurs as a result of the interaction between the laser and the water in rGO solution. We conclude that the population of oxigen defect in GQDs is increasing, following the increase of rGO concentration and could alter the optical properties of GQD. On the other hand, using Tauc’s plot, we confirm that the increase of rGO concentration as the ablated material does not alter GQDs optical band gap. However, it will slightly reduce both, direct and indirect Oxygen defect related optical band gap.

Two-photon induced excimer emission of dicyanoisophorone derivative in crystal state

In this work, two-photon induced excimer up-conversion emission of dicyanoisophorone derivative (1) in crystal state is described. 1 shows crystal emission, with one-photon excitation both monomer and excimer emission are detected. An enhanced excimer emission of 1 in crystal state has been observed with a 800nm Ti-sapphire femtosecond pulse laser, mechanism reveals that the enhanced excimer emission may result from the two-photon absorption. X-ray single crystal analysis demonstrates that the molecules of 1 adopt a face-to-face offset stacking mode in crystals, which benefits the excimers formation and emission.

Study on the effect of ambient gas on nanostructure formation on metal surfaces during femtosecond laser ablation for fabrication of low-reflective surfaces

Nanostructure formation on bulk metals (silver, gold, copper and titanium) by femtosecond Ti-sapphire laser irradiation (775nm, 150fs) is studied aiming the production of low-reflectivity surfaces and the better understanding of the development process. The experiments were performed in nitrogen, air, oxygen and helium environments at atmospheric pressure. The samples were irradiated with fluences in the 0.1–2J/cm2 range and an average pulse number of 100 falling over a given area. The reflectivity of the treated surfaces was determined by a microspectrometer in the 450–800nm range and their morphology was studied by scanning electron microscopy. The gas ambience influenced the results via two effects: formation processes and the chemically-induced modifications of the nanostructures. In case of He the nanoparticle aggregates–otherwise generally present–are predominantly missing, which leads to a lower darkening efficiency. The presence of oxygen enhances the darkening effect for copper mostly at lower fluences, while causes a slow increase in reflectivity in the case of titanium (in case of pure oxygen) in the high fluence range. The surface morphology in case of nitrogen and air were quite similar probably due to their close molecular mass values.

Nitrogen fluorescence induced by the femtosecond intense laser pulses in air

Our experiments show that external focusing and initial laser energy strongly influences filament generated by the femtosecond Ti–sapphire laser in air. The experimental measurements show the filament length can be extended both by increasing the laser energy and focal length of focusing lens. On the other hand, the plasma fluorescence emission can be enhanced by increasing the laser energy with fixed focal length or decreasing the focal length. In addition, the collapse distance measured experimentally are larger than the calculated ones owing to the group-velocity-dispersion effect. In addition, we find that the line widths of the spectral lines from $\text{N}_{2}$ is independent of filament positions, laser energies and external focusing.

Nonlinear optical response of platinum nanostructures and application for water detection in transformer oil

We report the fabrication of platinum nanostructures on an ITO substrate (Pt-NSs).

High harmonics generation at the interaction of an intense fs laser pulse with an overdense plasma layer

Harmonics generated with fs laser pulses are not only among the most intense sources in the wavelength range of a few tens of nanometers but also a far better source than X-ray lasers from the coherence point of view. It is anticipated, that in the near future, the harmonics issued from femtosecond laser-produced plasmas will represent a coherent source much brighter than all other XUV sources apart from the XFEL. These particular aspects, correlated with the fact that high order harmonics produced by reflection of an ultrashort and intense laser pulse on an overdense plasma layer impose virtually no restrictions on the intensity of the laser employed, lead the way to a series of potential applications in plasma diagnostics and nonlinear optics. This work presents a theoretical study on the high harmonics generation mechanism occurring at the reflection of a femtosecond Ti-Sapphire terawatt laser pulse (λ0 = 0.8 μm and pulse durations around 100–150 fs) on an overdense steep Al plasma layer. Insights on how different laser parameters influence this generation mechanism and its efficiency are provided.

Two-Photon Absorption of the DCM Molecule under Femtosecond Excitation between 720 and 920 nm

Nonlinear absorption of the DCM dye has been investigated by the two-quantum etalon method and the z-scan method with excitation by a tunable femtosecond Ti-sapphire laser (3 W, 140 fs, and 80 MHz). The two-photon absorption (TPA) spectrum of the DCM molecule has been obtained here for the first time between 720 and 920 nm and has been related to the absorption bands under linear excitation. It has been shown that in measurements of nonlinear absorption by the z-scan method the main contribution to changes in the transmittance comes from the triplet − triplet absorption.