Laser Excitation Research Articles

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.

Development of a cost-effective confocal Raman microscopy with high sensitivity

Confocal Raman microscopy is a powerful technique for identifying materials and molecular species; however, the signal from Raman scattering is extremely weak. Typically, handheld Raman instruments are cost-effective but less sensitive, while high-end scientific-grade Raman instruments are highly sensitive but extremely expensive. This limits the widespread use of Raman technique in our daily life. To bridge this gap, we explored and developed a cost-effective yet highly sensitive confocal Raman microscopy system. The key components of the system include an excitation laser based on readily available laser diode, a lens-grating-lens type spectrometer with high throughput and image quality, and a sensitive detector based on a linear charge-coupled device (CCD) that can be cooled down to −30 °C. The developed compact Raman instrument can provide high-quality Raman spectra with good spectral resolution. The 3rd order 1450 cm−1 peak of Si (111) wafer shows a signal-to-noise ratio (SNR) better than 10:1, demonstrating high sensitivity comparable to high-end scientific-grade Raman instruments. We also tested a wide range of different samples (organic molecules, minerals and polymers) to demonstrate its universal application capability.

Raman spectroscopy for classification of neoplastic and non-neoplastic CAM colon tumors

This paper demonstrates the potential of Raman spectroscopy for differentiating neoplastic from non-neoplastic colon tumors, obtained with the CAM (chicken chorioallantoic membrane) model. For the CAM model two human cell lines were used to generate two types of tumors, the RKO cell line for neoplastic colon tumors and the NCM460 cell line for non-neoplastic colon tumors. The Raman spectra were acquired with a 785 nm excitation laser. The measured Raman spectra from the CAM samples (n = 14) were processed with several methods for baseline correction and to remove artifacts. The corrected spectra were analyzed with PCA (principal component analysis). Additionally, machine learning based algorithms were used to create a model capable of classifying neoplastic and non-neoplastic tumors. The principal component scores showed a clear differentiation between neoplastic and non-neoplastic colon tumors. The classification model had an accuracy of 93 %. Thus, a complete methodology to process and analyze Raman spectra was validated, using a rapid, accessible, and well-established tumor model that mimics the human tumor pathology with minor ethical concerns.

Demonstration of Capture, Cooling, Tagging, and Spectroscopic Characterization of UV Photoproduct Ions in a Cryogenic Ion Trap: Application to 266 nm Photofragment Ions from Rhodamine 6G.

We demonstrate a method to determine the structures of the primary photodissociation products from a cryogenically cooled parent ion. In this approach, a target ion is cooled by a pulse of buffer gas and tagged in a 20 K Paul trap. The cold ion is then photodissociated by pulsed (∼5 ns) UV laser excitation, and the ionic products are trapped, cooled, and tagged by introduction of a second buffer gas pulse in the same trap. The tagged fragments are then ejected into a triple focusing, UV/vis/IR time-of-flight photofragmentation mass spectrometer which yields vibrational and electronic spectra of the mass-selected photofragments. These methods are demonstrated by application to the 266 nm photodissociation of the Rhodamine 6G cation to yield the R575 fragment ion based on loss of ethene as well as to a weaker secondary fragment arising from loss of m/z 43.

Topological Optical Waveguiding of Exciton‐Polariton Condensates

Abstract1D models with topological non‐trivial band structures are a simple and effective way to study novel and exciting concepts in topological photonics. In this work, the propagation of light‐matter quasi‐particles, so‐called exciton‐polaritons, is studied in waveguide arrays. Specifically, topological states are being investigated at the interface between dimer chains, characterized by a non‐zero winding number. In order to exercise precise control over the polariton propagation, non‐resonant laser excitation, as well as resonant excitation, are studied in transmission geometry. The results highlight a new platform for the study of quantum fluids of light and non‐linear optical propagation effects in coupled semiconductor waveguides.

Near-zero distortion in TCSPC at more than one photon per excitation period: experimental validation.

The time-correlated single-photon counting (TCSPC) technique is widely renowned for its capability of reconstructing rapid and weak light signals with exceptional sensitivity and sub-picosecond timing resolution. Unfortunately, the speed of TCSPC has been historically severely limited to avoid a phenomenon known as pileup distortion. For this reason, the count rate of a classic TCSPC acquisition channel is kept below a few percent of the laser excitation rate (usually 1%-5%). In this work, we experimentally validate a novel, to our knowledge, TCSPC theory recently reported that effectively overcomes such a limitation and finally achieves high-speed operation without distortion. Exploiting a single-photon avalanche diode (SPAD), in this paper we show how to acquire additional information about the status of the system at run time, and by combining it with the classic TCSPC data histogram, we report how a count rate of approximately 60% of the excitation frequency with near-zero distortion can indeed be achieved with a commercial system.

Laser enrichment of the 62Ni isotope for betavoltaic devices

We have studied the laser isotope separation of the 62Ni isotope using a three-step ladder type photoionization scheme. Using density matrix formalism, optimum conditions for the efficient separation of the 62Ni isotope have been derived. The optimum bandwidth of the excitation lasers has been found to be 200 MHz, 1200 MHz, and 1200 MHz for the enrichment of the 62Ni isotope. It has also been shown that it is possible to produce 75 mg/day of 90% enriched 62Ni using the optimized experimental operating parameters derived in this work. Upon irradiation of this enriched 62Ni isotopic mixture, it is possible to produce ∼19mg/day of the 63Ni isotope, which is sufficient to manufacture a 100 µW betavoltaic device each day.

Vector magnetometry in zero bias magnetic field using nitrogen-vacancy ensembles

Abstract The application of the vector magnetometry based on Nitrogen-Vacancy (NV) ensembles has been widely investigated in multiple areas. It has the superiority of high sensitivity and high stability in ambient conditions with microscale spatial resolution. However, a bias magnetic field is necessary to fully separate the resonance lines of optically detected magnetic resonance (ODMR) spectrum of NV ensembles. This brings disturbances in samples being detected and limits the range of application. Here, we demonstrate a method of vector magnetometry in zero bias magnetic field using NV ensembles. By utilizing the anisotropy property of fluorescence excited from NV centers, we analyzed the ODMR spectrum of NV ensembles under various polarized angles of excitation laser in zero bias magnetic field with a quantitative numerical model and reconstructed the magnetic field vector. The minimum magnetic field modulus that can be resolved accurately is down to ~0.64 G theoretically depending on the ODMR spectral line width (1.8MHz), and ~2 G experimentally due to noises in fluorescence signals and errors in calibration. By using 13C purified and low Nitrogen concentration diamond combined with improving calibration of unknown parameters, the ODMR spectral line width can be further decreased below 0.5 MHz corresponding to ~0.18 G minimum resolvable magnetic field modulus.

Super-Spectral-Resolution Raman spectroscopy using angle-tuning of a Fabry-Pérot etalon with application to diamond characterization

Raman spectroscopy is an extremely powerful laser-based method for characterizing materials based on their unique inelastic scattering spectrum. Ultimately, the power of the technique is limited by the resolution of the spectrometer. Here we introduce a new method for achieving Super-Spectral-Resolution Raman Spectroscopy (SSR-RS), by angle-tuning a Fabry–Pérot (F-P) etalon filter that we incorporated in a micro-Raman setup. A monolithically coated F-P etalon structure, only 1.686 mm in thickness, was mounted onto an angle-tunable motorized stage, and Raman spectra were automatically acquired for many different angles of the etalon. Using a low-resolution grating of 150 g/mm by itself, without the F-P etalon, we obtained a best-case regular Raman spectral linewidth of 44 cm−1 for the characteristic Raman peak from a diamond sample. When we applied the SSR-RS technique to diamond, we obtained a super-spectral resolution peak that was 27x narrower, namely 1.63 cm−1, and a Raman shift of 1331.3 cm−1. To baseline SSR-RS, we applied the super-spectral-resolution method to extract the linewidth and peak wavelength of the laser excitation itself and obtained a laser linewidth of better than 0.014 cm−1, with a laser wavelength centered at 531.962 nm, close to the stated wavelength of 532 nm. This extracted laser linewidth is 3300x times narrower compared to its measured linewidth of 46 cm−1. Thus, our work suggests that SSR-RS can be very generally applied to greatly improve the resolution and precision of Raman instrumentation, and potentially lower the cost of obtaining high-resolution Raman spectroscopic capabilities.

Unveiling Elegant In-Situ Properties: Structure and Vibrations of the Polymer Solution Synthesised BaFe12O19

The discovery of hexagonal ferrites has significantly contributed to various technological applications due to their unique ferromagnetic characteristics. This article employs the polymer solution technique for the first time in the synthesis of M-type hexaferrite, specifically BaFe12O19 (BaM). The polycrystalline nature of the BaM nanoparticles (NPs) is confirmed through X-ray diffraction (XRD) analysis, revealing a hexagonal structure within the P63/mmc space group. The study utilized the Scherrer method to assess the average crystallite size while utilizing the Williamson-Hall (W-H), Halder-Wagner (H-W), and Wagner-Auga (W-A) methods for a thorough analysis of XRD peak broadening, aiming to understand the relationship between crystallite size and intrinsic strain, demonstrating a high intercorrelation among the obtained results. In this work, XRD peak broadening analysis has been carried out by different models for the first time on BaM NPs. Fourier-transform infrared (FT-IR) spectroscopy was employed to designate the vibration behavior of chemical bonds, which confirms the formation of the hexagonal structure of BaM NPs. To assess the impact of excitation laser power in Raman spectroscopy, a study conducted a comprehensive analysis, comparing Raman spectra across excitation powers varied at 0.1 %, 0.5 %, 1 %, 5 %, and 10 %, maintaining a constant exposure time of 30 s throughout the experiment. Examination through Transmission Electron Microscopy (TEM) reveals a hexagonal rod-shaped morphology, with an average particle size falling within the range of 100 to 240 nanometers. The present study provides detailed insights about the structural, morphological, and compositional characteristics of BaM NPs for their utilization in high-frequency application. It shows a reflection loss (RL) of -13.68 dB at frequency of 10.3 GHz, with an absorption bandwidth of -10 dB spanning 0.42 GHz having 5 mm sample thickness.

Optical Characterization of the Interband Cascade LWIR Detectors with Type-II InAs/InAsSb Superlattice Absorber.

The long-wave infrared (LWIR) interband cascade detector with type-II superlattices (T2SLs) and a gallium-free ("Ga-free") InAs/InAsSb (x = 0.39) absorber was characterized by photoluminescence (PL) and spectral response (SR) methods. Heterostructures were grown by molecular beam epitaxy (MBE) on a GaAs substrate (001) orientation. The crystallographic quality was confirmed by high-resolution X-Ray diffraction (HRXRD). Two independent methods, combined with theoretical calculations, were able to determine the transitions between the superlattice minibands. Moreover, transitions from the trap states were determined. Studies of the PL intensity as a function of the excitation laser power allowed the identification of optical transitions. The determined effective energy gap (Eg) of the tested absorber layer was 116 meV at 300 K. The transition from the first light hole miniband to the first electron miniband was red-shifted by 76 meV. The detected defects' energy states were constant versus temperature. Their values were 85 meV and 112 meV, respectively. Moreover, two additional transitions from acceptor levels in cryogenic temperature were determined by being shifted from blue to Eg by 6 meV and 16 meV, respectively.

An Investigation of the Photonic Application of TeO2-K2TeO3-Nb2O5-BaF2 Glass Co-Doped with Er2O3/Ho2O3 and Er2O3/Yb2O3 at 1.54 μm Based on Its Thermal and Luminescence Properties.

A glass composition using TeO2-K2TeO3-Nb2O5-BaF2 co-doped with Er2O3/Ho2O3 and Er2O3/Yb2O3 was successfully fabricated. Its thermal stability and physical parameters were studied, and luminescence spectroscopy of the fabricated glasses was conducted. The optical band gap, Eopt, decreased from 2.689 to 2.663 eV following the substitution of Ho2O3 with Yb2O3. The values of the refractive index, third-order nonlinear optical susceptibility (χ(3)), and nonlinear refractive index (n2) of the fabricated glasses were estimated. Furthermore, the Judd-Ofelt intensity parameters Ωt (t=2,4,6), radiative properties such as transition probabilities (Aed), magnetic dipole-type transition probabilities (Amd), branching ratios (β), and radiative lifetime (τ) of the fabricated glasses were evaluated. The emission cross-section and FWHM of the 4I13/2→4I15/2 transition around 1.54 μm of the glass were reported, and the emission intensity of the visible signal was studied under 980 nm laser excitation. The material might be a useful candidate for solid lasers and nonlinear amplifier devices, especially in the communications bands.

Photoluminescence Confocal Mapping of a Novel Nd3+/Yb3+: Zn2SiO4 Composite thin film on Si (100) Substrate Utilizing a 980nm Pumping Source.

A fixed Nd3+ and varied Yb3+ ion concentration were incorporated in a Zinc-Silicate (SZNYX) composite solution using ex-situ sol-gel solution to fabricate a novel thin film (TF) on Si (100)-substrate. The upconversion luminescence (UCL) spectra of the thin films were measured under 980nm laser excitation, with the most optimized result for Yb3+ ion concentration of 1.5mol%. Additionally, a 2-D photoluminescence (PL) confocal mapping of the SZNY15-TF material confirmed uniform PL distribution throughout the space under the same excitation wavelength. Structural characterization via XRD revealed the tetragonal Zn2SiO4 nano-crystalline nature of the film at three distinct annealing temperatures. Morphological characterization using the Field-emission scanning electron Microscope (FESEM) coupled with energy dispersion spectrometer (EDS) affirmed the nanoflower structure and the purity of doping purity in the samples, respectively. These findings collectively confirm the promising UCL properties of the SZNYX-TF samples, suggesting potential applications in photonic.

Antibody-Based Array for Tacrolimus Immunosuppressant Monitoring with Planar Plastic Waveguides Activated with an Aminodextran-Lipase Conjugate.

Cyclic olefin copolymers (COC; e.g., Zeonor, Topas, Arton, etc.) are materials with outstanding properties for developing point-of-care systems; however, the lack of functional groups in their native form makes their application challenging. This work evaluates different strategies to functionalize commercially available Zeonor substrates, including oxygen plasma treatment, photochemical grafting, and direct surface amination using an amino dextran-lipase conjugate (ADLC). The modified surfaces were characterized by contact angle measurements, Fourier transform infrared-attenuated total reflection analysis, and fluorescence assays based on evanescent wave excitation. The bioaffinity activation through the ADLC approach results in a fast, simple, and reproducible approach that can be used further to conjugate carboxylated small molecules (e.g., haptens). The usefulness of this approach has been demonstrated by the development of a heterogeneous fluorescence immunoassay to detect tacrolimus (FK506) immunosuppressant drug using an array biosensor platform based on evanescence wave laser excitation and Zeonor-ADLC substrates. Surface modification with ADLC-bearing FK506 provides a 3D layer that efficiently leads to a remarkably low limit of detection (0.02 ng/mL) and IC50 (0.9 ng/mL) together with a wide dynamic range (0.07-11.3 ng/mL).

Study of SiGeAsTe and SiGeAsSe chalcogenide thin films by Raman spectroscopy and understanding of their OTS properties

In this paper, a range of sputtered ternary and quaternary (Si)(Ge)AsxTe3 layers (x: 2 or 5) and (Si)(Ge)As2Se3 layers are examined using Raman spectroscopy. The results are linked to the Ovonic Threshold Switching properties of these materials when incorporated in selector devices, as observed in separate studies. In case of both the As-rich and As-poor tellurides, a large amount of homopolar bonds are present as the spectra are dominated by peaks associated with As–As and Te–Te bonds. Such homopolar bonds are commonly linked with drift in OTS properties. In the case of the selenides the spectra are dominated by modes associated with heteropolar As–Se bond vibrations. Adding Ge as an alloying element has a significant impact on the bond structure for both material systems. In contrast, Si has a much less pronounced impact and will mostly bond with itself. Time-resolved Raman measurements were also performed to determine the stability of the layers under micro-Raman laser excitation. At the regular exposure settings, no significant changes in the spectra were observed during the measurement. At elevated exposure settings, however, persistent changes in the bond structure can be induced for certain compositions.

Stable optical response during electron–phonon equilibration in laser-excited gold

We study the optical response of solid gold driven by ultrashort pulses of visible light by tracking the conduction band density and damping rates. While we find rapid changes in optical properties during and shortly after the laser excitation, we obtain an almost unchanged reflectivity during the stage of electron–phonon temperature equilibration. These predictions are in good agreement with experimental data and exhibit a strong compensation of damping mechanisms as a source for the stable response, although electron and ion temperatures change significantly. Considering the complex interplay of damping processes in solid gold, our model gives a more fundamental interpretation of optical measurements than existing approaches.

Effect of wavelength and liquid on formation of Ag, Au, Ag/Au nanoparticles via picosecond laser ablation and SERS-based detection of DMMP.

The present study investigates the effects of input wavelength (1064, 532, and 355 nm) and surrounding liquid environment (distilled water and aqueous NaCl solution) on the picosecond laser ablation on silver (Ag), gold (Au), and Ag/Au alloy targets. The efficacy of the laser ablation technique was meticulously evaluated by analyzing the ablation rates, surface plasmon resonance peak positions, and particle size distributions of the obtained colloids. The nanoparticles (NPs) were characterized using the techniques of UV-visible absorption, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Furthermore, NPs of various sizes ranging from 6 to 35 nm were loaded onto a filter paper by a simple and effective drop-casting approach to achieve flexible surface-enhanced Raman spectroscopy (SERS) substrates/sensors. These substrates were tested using a simple, portable Raman device to identify various hazardous chemicals (malachite green, methyl salicylate, and thiram). The stability of the substrates was also systematically investigated by determining the decay percentages in the SERS signals over 60 days. The optimized SERS substrate was subsequently employed to detect chemical warfare agent (CWA) simulants such as methyl salicylate (a CWA simulant for sulfur mustard) and dimethyl methyl phosphonate (has some structural similarities to the G-series nerve agents) at different laser excitations (325, 532, and 633 nm). A notably higher SERS efficiency for CWA simulants was observed at a 325 nm Raman excitation. Our findings reveal that a higher ablation yield was observed at IR irradiation than those obtained at the other wavelengths. A size decrease of the NPs was noticed by changing the liquid environment to an electrolyte. These findings have significant implications for developing more efficient and stable SERS substrates for chemical detection applications.

Raman enhancement via double optical resonances in all-dielectric photonic crystal slabs

All-dielectric photonic structures are an important class of substrates in surface-enhanced Raman spectroscopy (SERS), utilizing optical resonant modes to significantly enhance the electromagnetic field and amplify the Raman signals. In this study, we demonstrate the double-resonance approach to realize significant Raman enhancement using all-dielectric photonic crystal (PhC) slab. The double-resonance condition is satisfied by designing optical resonant modes in photonic bands to match frequencies of both excitation laser and Raman signals. By the fabricated PhC slab, the significant enhancement for the Raman signal of silicon is demonstrated. The enhanced Raman signals exhibit a uniform distribution on the PhC slab. The method of Raman enhancement via double optical resonances can advance the field of all-dielectric SERS and holds potential for future SERS applications.

Microwave assisted preparation of ternary scheelite CaMoO4: Er3+/Yb3+ nano-phosphors for up/down-conversion photoluminescence, temperature sensing and antibacterial properties

Due to their exceptional intrinsic optical characteristics, molybdate compounds have aroused significant attention in recent years for their effective up and downconversion luminescence. In the present study, a series of xEr3+/Yb3+ (x = 0.5 %, 1 %, 2 %, 4 % and Yb3+ =15 %) doped CaMoO4 nanophosphors synthesized through a microwave assisted approach and subsequently the comprehensive analysis of the functionalities such as optical properties, antibacterial traits and their integration with temperature sensing, have been explored. Furthermore, the structural refinement confirms the occurrence of tetragonal scheelite phase of the prepared materials. The morphology of the material was identified by FE-SEM and HR-TEM analysis which reveals particles are in spherical shape. Up-conversion luminescence intensities were found to be dependent on doping concentration, laser excitation power and external temperature upon 980 nm light excitation. The temperature sensing response of the optimized sample was examined based on intensity ratio of two emission bands that involves thermally connected energy levels of Er3+ ion. The maximum absolute sensitivity of 10.74 × 10−3 K−1 (at 500 K) was found, demonstrating its potential application in high temperature thermometry. The comprehensive analysis and the outcome of the present study suggests the potential prospect of the as-synthesized material in food preservation, medical equipment, water treatment, and as an optical coating agent for solid state luminous devices.

Exceptional point sensing via energy loss profile in a non-Hermitian system

The heightened sensitivity observed in non-Hermitian systems at exceptional points (EPs) has garnered significant attention. Typical EP sensor implementations rely on precise measurements of spectra and importantly, for real time sensing measurements, the EP condition ceases to hold as the perturbation increases over time, thereby preventing the use of high sensitivity at the EP point. In this work, we present an new approach to EP sensing which goes beyond these two traditional constraints. Firstly, instead of measuring the spectra, our scheme of EP based sensing is based on the observation of decay length of the optical mode in finite size gratings, which is validated via coupled mode theory as well as full wave electrodynamic simulations. Secondly, for larger perturbation strengths, the EP is spectrally shifted instead of being destroyed — this spectral shift of the EP is calibrated and using this look-up table, we propose continuous real time detection by varying the excitation laser wavelength. As a proof of principle of our technique, we present an application to the sensing of coronavirus particles, which shows unprecedented limit of detection. Furthermore, our analysis includes calculation of the signal-to-noise ratio, revealing that EP sensors offer advantage when classical technical noise dominates over fundamental noise. These findings will contribute to the expanding field of exceptional point based sensing technologies for real time applications beyond spectral measurements.