Sapphire Laser Research Articles

Probing nonperturbative third and fifth harmonic generation on silicon without and with thermal oxide layer

We examine Si with and without additional SiO2 thin film coating as a candidate for producing powerful 3rd and 5th harmonics of Ti:sapphire laser pulses for future spectroscopic application. Polarization rotation experiments have been performed at different incident angles to determine the origin of the generated harmonics and a strong polarization-dependency of the harmonic signals was observed. A simplified tensor formalism is introduced to reproduce the measurements with high accuracy. Comparing the measurements with the Oh symmetry of the bulk crystal, the C2v structural symmetry for the uncoated Si sample and a C4v symmetry for the SiO2 coated sample, we conclude that the polarization anisotropies are determined by the surface/interface symmetries.

Hong-Ou-Mandel interference with a diode-pumped 1-GHz Ti:sapphire laser

Correlated photon pairs generated through spontaneous parametric down-conversion (SPDC) are a key resource in quantum optics. In many quantum optics applications, such as satellite quantum key distribution (QKD), a compact, high repetition rate pump laser is required. Here we demonstrate the use of a compact, GHz-rate diode-pumped three-element Kerr-lens-modelocked Ti:sapphire laser for the generation of correlated photon pairs at 790 nm. We verify the presence of indistinguishable photons produced via SPDC using Hong-Ou-Mandel (HOM) interferometry and observe a dip in coincidence counts with a visibility of 81.8%.

High-intensity single-pulse extraction using a laser-activated GaAs reflective switch for a terahertz free-electron laser

Single-pulse extraction from a terahertz (THz) pulse train is demonstrated for a free-electron laser oscillator using the laser-activated semiconductor switching technique with gallium arsenide (GaAs). Using a GaAs wafer as the switching substrate and a titanium sapphire laser (Ti:sapphire laser), a single THz pulse can be extracted with a high contrast from the pulse train at intervals of 37 ns in a simple experimental setup due to a short decay time of the electron–hole plasma. For a single THz pulse with a duration of a few to a few tens of picoseconds and a nominal wavelength of 70μm, we achieve an extracted single pulse energy of 76 μJ.

High-Power and High-repetition-rate widely tunable Narrow-Linewidth low-gain-band Ti: Sapphire laser

High-Power and High-repetition-rate widely tunable Narrow-Linewidth low-gain-band Ti: Sapphire laser

Stimulated Raman scattering of chirped Ti:sapphire laser pulse in BaWO4, SrMoO4 and Ca3(VO4)2 crystals

Transient stimulated Raman scattering (SRS) of chirped, temporally stretched up to 45 ps, Ti:sapphire laser pulses was studied in three different Raman-active crystals (BaWO4, SrMoO4 and Ca3(VO4)2) at the same experimental conditions. BaWO4 and SrMoO4 crystals had the same SRS “threshold” energy/intensity, which was associated with their similar integrated cross sections for spontaneous Raman scattering. The highest energy SRS efficiency was obtained in SrMoO4 crystal and reached 8%, which was two-times higher than one in BaWO4. Higher SRS efficiency in SrMoO4 was observed due to lower nonlinear absorption. The Ca3(VO4)2 crystal had significantly higher SRS “threshold” and lower efficiency despite the lowest nonlinear absorption losses. A simple expression of exponential gain for transient SRS of chirped laser pulses was proposed and verified by comparison with experimental results. This expression was used to estimate dephasing time T2 of Ca3(VO4)2 crystal which was 8.5 ± 1.0 ps.

Nonlinear Refraction, Excited State Absorption, and Multiphoton Absorption of 1,3-Thiazolium-5-thiolate Mesoionic Compound.

We synthesized the mesoionic compound 2-(4-chlorophenyl)-3-methyl-4-(4-methylphenyl)-1,3-thiazole-5-thiolate and measured its refractive and absorptive nonlinear optical response in different temporal and spectral regimes. The experiments were performed by using the Z-scan technique with two pulsed light sources: the second harmonic (at 532 nm) of a mode-locked and Q-switched Nd-YAG laser (100 ps, 10 Hz) and a Ti: Sapphire laser system (100 fs, 1 kHz) operating at 800 nm. The observation and characterization of nonlinear refraction, two- and three-photon absorption, and excited state absorption of the mesoionic compound dissolved in dimethyl sulfoxide, in different concentrations, are presented and discussed with basis on the population redistribution in a three-energy-level model that allows the determination of the parameters which characterize the nonlinear response.

Polymorphism and up-conversion photoluminescence properties of Y2WO6 doped with Yb3+/Er3+ under excitation at 975 nm

This article reports the synthesis and luminescent properties (up-conversion and down-shifting) of the tetragonal and orthorhombic polymorphs of Y2WO6 doped with Erbium (Er3+) and Ytterbium (Yb3+) cations. The syntheses were carried out by a high temperature solid state reaction. The orthorhombic phase was prepared by pressing the parent compounds into pellets of 13 mm diameter. The samples were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Luminescence up-conversion measurements were analyzed using a tunable continuous wave (CW) Ti:sapphire laser system tuned at 975 nm. The results show that the green up-conversion emission is more intense than the red one in both polymorphs. To gain further clarity on this matter, we have also conducted a study on down-shifting emission spectra measured at 378 nm, where only the strong green emission is observed. The pump power dependence and the decay curves of the (4S3/2 → 4I15/2) transition were also evaluated.

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.

High-power, low-phase-noise, frequency-agile laser system for delivering fiber-noise-canceled pulses for strontium clock atom interferometry.

We present a laser system for performing single-photon atom interferometry on the 698 nm clock transition in ultracold strontium. We coherently combine the power of two titanium:sapphire lasers and demonstrate chirps of 200 MHz in 2.5 ms while phase-locked to an optical reference. Moreover, we demonstrate a novel, to the best of our knowledge, scheme to deliver 4 W pulsed beams to the atoms via a mode-cleaning optical fiber using active noise cancellation.

Dynamics of laser-induced formation of color centers in a lithium fluoride crystal

The dynamics of the laser-induced formation of aggregate color centers under the action of the first (950 nm) and second (475 nm) harmonics of a femtosecond Ti:sapphire laser has been studied. During the irradiation of the samples with laser radiation, the photoluminescence spectra of the induced centers were repeatedly measured. It was found that intensity of the spectral luminescence band of F3+ centers exceeds intensity of the band of F2 centers in samples with color centers induced by the first harmonic. At the same time, the opposite ratio of the intensities of these bands was observed in the luminescence spectra of color centers produced by second harmonic radiation for the same energy of laser pulses. It has been established that the observed effect is caused by different degree of heating of the crystalline medium in the regions of passage of laser filaments. Heating accelerates the migration of kinetic particles that carry out the aggregation process. The ratio of the concentrations of F2 and F3+ centers depends on the ratio of the duration of irradiation and the lifetime of kinetic particles, which significantly depends on temperature. A multiphoton-tunneling mode of interband ionization of a crystalline substance was implemented in the experiment. It is shown that the identity of the absorption spectra of color centers induced by the first and second harmonics of femtosecond laser radiation is a new distinguishing characteristic of experimental implementation of the tunneling ionization mechanism in experiment.

Caries affected disinfection using Phycocyanin activated by PDT, Holy Basil, and Ti-sapphire laser on adhesive bond strength, microleakage, and bond failure

AIMTo investigate the effect of different cavity disinfectants, Phycocyanin (PC), Ocimum Sanctum (OS), and Ti Sapphire Laser, on the bond integrity and microleakage of resin restorations. Material and method60 human mandibular molars were extracted and prepared based on ICDAS scores of 4 and 5. To obtain the CAD surface, a visual examination was supported by tactile sensation and a dye for caries detection. Samples were randomly allocated into 4 groups based on cavity disinfectants applied (n = 15). Group 1: Specimens disinfected with CHX, Group 2: Specimens disinfected with Ti sapphire laser, Group 3: Specimens disinfected with Phycocyanin activated by Photodynamic therapy, and Group 4: Specimens disinfected with OS. Following the disinfection of the CAD surfaces, composite bulk-fill restorative material was bonded to each specimen and all samples were subjected to thermocycling. Ten samples from each group underwent SBS testing performed on a universal testing machine. Five samples were subjected to a microleakage analysis. ResultThe maximum microleakage scores were displayed by Group 3: PC (0.521 nm) treated specimens. Whereas, and minimum microleakage was exhibited by Group 4: OS (0.471 nm). Group 4: OS (23.06±0.21 MPa) treated group displayed the maximum bond scores of resin adhesive to the CAD surface. However, Group 3: PC (21.67±0.24 MPa) treated specimens exhibited the lowest bond scores. Failure mode analysis revealed that among all the investigated groups the predominant type of failure was cohesive failure i.e., Group 1 (80%), Group 2 (80%), Group 3 (70%), and Group 4 (90%). ConclusionOcimum Sanctum, Phycocyanin activated by Photodynamic therapy, and Ti-sapphire laser for disinfection of caries-affected dentin have shown promise in terms of improved bond strength and reduced microleakage

Efficacy of Er.Cr.YSGG Laser, Ti Sapphire Laser and Zinc Pthalocyanine (TM ZnPc) Apical Root Canal Treatment on Smear Layer Removal. A Scanning Electron Microscopy Study

Aims: Comparison of the smear layer-removing capacity of several final irrigants (Er, Cr: YSGG laser (ECL), zinc phthalocyanine (TM-ZnPc), titanium: sapphire laser (Ti)) employed in the apical third of radicular dentin to and ethylenediamine tetraacetic acid (EDTA). Material and Methods: The chamber was opened, and 15 K file established canal patency. TruNatomy prime shaping files treated root canals. Root canal disinfectant was 3 mL of 2.25 NaOCl between each file. After disinfection, the teeth were randomly divided into four groups (n = 10). Groups 1–4:17% EDTA, ECL, Ti: sapphire laser, and TM-ZnPc. The root was separated by chiseling longitudinal grooves on the mesial and distal surfaces. SEM magnification at 5000X was used to evaluate smear layer removal based on dentinal tubule patency in the apical one-third of root canals using Gutman et al. grading system. IBM-SPSS 23.0 analyzed data. One-way ANOVA and Tukey’s post hoc test compared groups. p =0.05. Results: Group-2 (NaOCl+ECL) specimens removed the most smear layer. Group-4 (NaOCl+TM-ZnPc) removed the least smear layer. Group-1 (NaOCl+EDTA), Group-2, and Group-3 (NaOCl+Ti sapphire laser) showed equivalent smear layer removal efficacy. Conclusion: Er: Cr, YSGG, and Ti: sapphire laser with sodium hypochlorite has the potential to remove the apical third smear layer.

Evidence of Yb3+ band broadening and continuous wave laser operation in bismuth modified KY1-x-yBixYby(WO4)2 mixed single crystals

To increase the Yb3+ optical bandwidths in highly anisotropic β:KY(WO4)2 (KYW) type laser single crystals, the simultaneous contributions of the Bi3+ 6 s2 lone electron pair and Y3+/Bi3+ ionic radii mismatch is proposed. The top seeded solution growth method with K2W2O7 as solvent was used to grow Yb doped single crystals of the KY(WO4)2/KBi(WO4)2 (KYBiW) solid solution. Crystals obtained across the used KY1xBixW solid solution range show always the low temperature β phase, with the monoclinic C2/c crystalline structure, but important differences between the Y/Bi composition of the starting solute and that of the crystal grown are found. The incorporation of Y and Yb into the crystal is preferential, resulting in a low Bi segregation coefficient, SBi= 13%, on the KYW side but near SBi= 90% in the KBiW side (Yb is still strongly incorporated filling the remaining 10%). The saturation temperature of the melt decreases as the Bi concentration in the precursor KY1-x-yBixYby(WO4)2/K2W2O7 mixture increases. Evidence of optical absorption and photoluminescence broadening of the Yb3+ bands with Bi3+ incorporation is derived from 6 K and 300 K measurements. Laser operation of KY1-x-yBixYby(WO4)2 crystals is shown to be comparable to that of KY1−yYby(WO4)2 ones. Up to ≈ 0.5 W of output power is obtained pumping in continuous wave regime with a Ti sapphire laser with slope efficiency η ≈ 65% and pump threshold< 200 mW, which is within the usual performance of KYW:Yb crystals, but the spectral distribution of the laser output in KYBiW:Yb crystals is larger than that for KYW:Yb. This spectral broadening may help in the reduction of ultrashort (fs) laser pulse duration generated by modelocking.

Generation of sub-MV/cm terahertz fields with large-size Cherenkov-type optical-to-terahertz converters.

It is known that a structure comprising a tens of microns thick, and ∼1 × 1 cm2 in size, layer of LiNbO3 attached to a Si prism can serve as an efficient Cherenkov-type converter of tens of microjoules-energy femtosecond laser pulses to broadband terahertz radiation. Here we experimentally demonstrate scaling up the terahertz energy and field strength by extending the width of the converter to several centimeters, expanding appropriately the pump laser beam, and increasing the pump pulse energy to hundreds of microjoules. In particular, chirped Ti:sapphire laser pulses of 450 fs duration and 600 µJ energy were converted to 1.2 µJ terahertz pulses, and 0.5 MV/cm peak terahertz field was obtained when pumping by unchirped laser pulses of 60 fs duration and 200 µJ energy.

Micro-Photoluminescence spectroscopy of two distinct types of WS2 monolayers using fs-Ti: Sapphire laser under vacuum and ambient conditions and multivariate calibration models

We utilized Micro-Photoluminescence (μPL) and time-resolved photoluminescence (TRPL) spectroscopies with a femtosecond laser (440 nm) to assess the optical properties of two types of WS2 monolayers (MLs) obtained through mechanical exfoliation of different crystals. Based on cryogenic μPL spectra (4 K), the monolayers were classified as low-defect-concentration (LDC) and high-defect-concentration (HDC). By subjecting the MLs to laser excitation at various photon fluxes under ambient and vacuum conditions at room temperature, we characterized their optical properties. The spectra exhibited two main regions corresponding to optical transitions of neutral excitons (X) and trions (T). Notably, two distinct regimes were observed for quasi-particle decay: X-X annihilation at low photon fluxes and Mott transition at high photon fluxes. The photoluminescence quantum yield (PLQY) was measured under ambient and vacuum conditions, with the presence of physisorbed O2 on the ML surface influencing the results. Additionally, we employed a novel analytical approach combining PL and TRPL spectra with chemometric methods for the regression analysis of the two types of WS2 MLs. Utilizing partial least squares regression and principal component regression models, we estimated the decay times of X and T quasi-particles based on the spectral datasets.

Er, Cr: YSGG, Nd: YVO4, and Ti: Sapphire Lasers for Surface Treatment of Hybrid Ceramics on Bond Durability, Surface Texture, and Debonding to Resin Cement: A Scanning Electron Microscopy (SEM) Analysis

Aims: To assess composite ceramics treated with Er, Cr: YSGG (ECL), Nd: YVO4, and Ti: Sapphire lasers to samples treated with hydrofluoric acid (HF) and silane (S) for shear bond strength (SBS) and surface roughness (Ra). Material and Methods: 60 disc-shaped HRC specimens. Surface conditioning techniques divided HRC-prepared discs into four groups. Samples in Group 1: HRC pretreated with normal 9.5% HF, Group 2: ECL, Group 3: Ti-Sapphire, Group 4: Nd: YVO4. The profilometer measured all ceramic discs’ average surface Ra. Universal testing machines tested the resin-ceramic interface SBS. Surface topography was assessed using SEM. Shear bond scores and Ra were compared using a one-way ANOVA. A Tukey’s post hoc test assessed several group comparisons. Results: Group 2 (Ti Sapphire Laser+S) samples scored highest in Ra and SBS. Group 4 Nd: YVO4+S had the lowest Ra and SBS values. HF 20 sec+S, (Ti Sapphire Laser+S), (ECL+S), and (Nd: YVO4+S) had comparable SBS and Ra values (p&gt;0.05). Conclusion: Laser-conditioned hybrid ceramics Er, Cr: YSGG, Nd: YVO4, and Ti-Sapphire lasers have shear bond strength and surface roughness comparable to 9.6% hydrofluoric acid.

Investigation of thermal decomposition of nitrobenzene: An energetic material

Oxidation and pyrolysis mechanisms of energetic materials shape their macro properties such as autoignition and detonation. The high reaction-enthalpy, microsecond order reaction time, and toxicity necessitate investigation of their detailed chemical kinetics. A shock tube combined with laser absorption diagnostic provides time-resolved, high-sensitivity, and homogeneous environment to study thermal degradation of energetic and hazardous materials. In this work, we investigated the thermal fragmentation of nitrobenzene (C6H5NO2), a prototypical energetic material and nitro-aromatic representative, behind reflected shock waves. We studied its pyrolysis and decomposition branching channels over temperatures of 1155–1434 K and pressures of 0.82–1.78 bar. Channel-specific branching ratio was determined by employing a two-color laser absorption diagnostic. Two decomposition pathways are found to be significant under our experimental conditions. The first channel (k1) produces phenyl radical (C6H5) and NO2 while the second channel (k2) generates phenoxy radical (C6H5O) and NO. We monitored the reaction progress by tracing channel-specific products, i.e., phenyl radical (C6H5) and NO, using ultraviolet–visible (UV–vis) and infrared (IR) absorption diagnostics. UV–vis light at 445 nm for phenyl radical detection came from the frequency doubling of 890 nm light, generated by a titanium–sapphire laser, which was pumped by a green (532 nm) Nd:YAG laser. IR light at 5.517 μm for NO detection was generated by an external-cavity quantum cascade laser. We extracted the rate coefficients of the two decomposition channels and fitted them in Arrhenius form (units of s−1):k1=8.49×1014exp(−30476KT)k2=2.31×1013exp(−27618KT)Rate coefficients of both channels show positive temperature dependence while we did not observe discernible pressure dependence over 0.82–1.78 bar. Our measurements agree with a previous theoretical work qualitatively that, under these high-temperature conditions, the decomposition channel producing phenyl radicals and NO2 (k1) prevails over the NO-producing channel. Quantitatively, however, the theoretical work overestimates the importance of k1 channel, particularly at low temperatures. Our rate of production analysis shows that most of the phenyl radicals are consumed through their self-recombination while N atoms are mainly converted to NO2. This work benefits high-fidelity chemical modeling of the relevant safety and ignition aspects of nitrogen-containing energetic/hazardous materials.

Facile Suzuki Coupling Strategy toward New Nile Red Derivatives with Improved Two‐Photon Brightness

AbstractChemical fine‐tuning of fluorophores is a pivotal step towards development of next generation fluorescent dyes for microscopy. With the advent of high‐resolution two‐photon excitation fluorescence imaging, there is a growing demand for very sensitive laser dyes that can be efficiently excited using commercial Ti:sapphire laser sources in the first near‐infrared window (NIR‐I, 780–1020 nm). Using the fluorescent dye Nile Red as the lead structure, we report a robust and concise Suzuki coupling approach for the synthesis of 14 new Nile Red analogues that feature extended π ring systems and diverse functionalities. For this set, we gauged their two‐photon excitation efficiency in NIR‐I as well as evaluated their general fluorescent properties (emission wavelength, Stokes shift, quantum yield and solvatochromism). Several of the new fluorophores were found to display very favorable characteristics. In particular, the derivative featuring a 4‐aminophenyl group in the 2‐position of Nile Red exhibited extreme solvent sensitivity, and the thien‐2‐yl substituted Nile Red derivative showed significantly redshifted emission, large Stokes shift and high two‐photon brightness.

Frequency Locking of the Titanium–Sapphire Laser by Resonant Absorption Lines of a Cesium-Vapor Cell in a Cavity

Frequency Locking of the Titanium–Sapphire Laser by Resonant Absorption Lines of a Cesium-Vapor Cell in a Cavity

Sub-pm linewidth, high pulse energy, high beam quality microsecond-pulse Ti:sapphire laser at 766.699 nm.

In this letter, a sub-pm linewidth, high pulse energy and high beam quality microsecond-pulse 766.699 nm Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. At an incident pump energy of 824 mJ, the maximum output energy of 132.5 mJ at 766.699 nm with linewidth of 0.66 pm and a pulse width of 100 µs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, this is the highest pulse energy at 766.699 nm with pulse width of hundred micro-seconds for a Ti:sapphire laser. The beam quality factor M2 is measured to be 1.21. It could be precisely tuned from 766.623 to 766.755 nm with a tuning resolution of 0.8 pm. The wavelength stability is measured to be less than ±0.7 pm over 30 min. The sub-pm linewidth, high pulse energy and high beam quality Ti:sapphire laser at 766.699 nm can be used to create a polychromatic laser guide star together with a home-made 589 nm laser in the mesospheric sodium and potassium layer for the tip-tilt correction resulting in the near-diffraction limited imagery on a large telescope.