NIR Lasers Research Articles

Photon diagnostics at the FLASH THz beamline.

The THz beamline at FLASH, DESY, provides both tunable (1-300 THz) narrow-bandwidth (∼10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.

Optical properties of Er3+/Yb3+ co-doped phosphate glass system for NIR lasers and fiber amplifiers

In this research, the optical properties of Er3+/Yb3+ co-doped phosphate glass have been studied to explore the potential of this glass system in laser and electronic amplifiers. The Judd–Ofelt (J-O) intensity parameter (Ωt) in the J-O model was established to determine the absorption intensity of the glass. The optical properties of the glass can be evaluated by various radiation parameters such as the radiative transition probabilities (Arad), stimulated emission cross sections (σe), branching ratios (βJJ'), maximum half-width values (Δλp), and the radiation lifetime (τrad) of the glass. It was found that in the case of Yb3+ as a sensitizer, the spectral properties of the Er3+ doped glass can be maximized. The data of Arad, βJJ', τrad, σe and Δλp obtained by Er3+/Yb3+ co-doping can find that the Er3+-doped sample undergoes 4I13/2–4I15/2 transition at 1.56 µm, and the stimulated emission cross section is greatly improved. The application prospects of the glass in solid near-infrared laser and electronic communication was discussed. According to the comprehensive discussion and analysis, the glass has great application potential.

Manipulating Light in Coupled Asymmetric Nanostructures Induced by a Visible–NIR Laser

We design an asymmetric nanostructure in the longitudinal direction at the visible–NIR range, which enables high enhancement factor and has the properties of Fano resonance induced by a visible–NIR laser. By simulating and analyzing the resonance frequency spectra of various nanorods, nanodipoles, and combined nanoantennas, we optimize the resonant spectra and enhanced factor of such nanoantennas. It has broad-band resonant spectra with a FWHM from 800 to 1,100 nm and possesses two resonant peaks at 870 and 1,000 nm, with an enhancement factor of 24. The current density distribution in such nanoantennas with different phases is also simulated in order to investigate its resonant mode. This theoretical study paves the way towards nanoscale lightwave control and spectral splitting. The designed nanodevices provide great potential for applications in ultrasensitive color sorters and biosensors induced by visible–NIR lasers.

Nd3+-doped heavy metal oxide based multicomponent borate glasses for 1.06 μm solid-state NIR laser and O-band optical amplification applications

Nd3+-doped glasses in the composition (50-x) B2O3-10 PbO-10 BaO-10 Al2O3-10 ZnO-10 Na2O-(x) Nd2O3 (x = 0.0, 0.1, 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 mol %) were fabricated using melt quenching method. Upon 592 nm visible and 808 nm LD excitations, the luminescence spectra show a strong 4F3/2 → 4I11/2 (1.06 μm) emission transition, and two less intense 4F3/2 → 4I9/2 (0.89 μm) and 4F3/2 → 4I13/2 (1.331 μm) emission transitions. The intensity of such emissions increases up to 0.5 mol % Nd3+, and above this doping level, quenching occurs. For 0.5 mol % Nd3+-doped glass, following Judd–Ofelt intensity parameters and emission spectrum, AR, τR, βR and βexp, including Δλeff,σem(λp), (σem × (Δλeff)) and (σem × (τrad)), are derived for Nd3+ ion 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 fluorescence transitions. The highest σem(λp) for the 1.06 and 1.331 μm fluorescence bands are found to be 6.216 × 10−20 and 2.295 × 10−20cm2, respectively. The 4F3/2 level lifetimes are found to decrease with an increase in Nd2O3 content and the decay curves of the glass up to 1.5 mol % Nd3+ exhibit single exponential nature. From ‘τexp’ of the Nd3+: 4F3/2 level, quantum efficiency (η), (σem × (τexp)), and saturation intensity (IS) are 48.87%, 51.09 × 10−25 cm2s and 3.67 × 108 W/m2, respectively, for the 0.5 mol % Nd3+-doped glass. Higher thermal stability, very low χ, high AR, large βexp., moderate τR, large gain bandwidth and high optical gain values indicate that 0.5 mol % Nd3+-doped glass could be a potential gain medium for solid-state NIR lasers at 1.06 μm. Moreover, for the 1.331 μm emission, large Δλeff and the theoretical gain coefficient value of 1.579 dB/cm, evaluated with an excited Nd3+ ion fractional factor of 0.6, indicate that this glass might be a promising candidate in developing O-band optical fiber amplifiers.

Optical properties of Er3+/Yb3+ co-doped bismuth calcium borate glass system for NIR lasers and fiber amplifiers

An Er3+/Yb3+ co-doped bismuthate (Bi2O3-B2O3-CaO) glass was prepared by melt quenching method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), absorption and emission spectroscopy. The Judd-Ofelt parameters (Ωλ) were determined from the intensity of the absorption band to calculate the radiation parameters, such as the radiation lifetime (τrad), radiation transition probability (Arad) and branching ratio (βJJ′) of 4I13/2 laser conversion of Er3+ ions. The effective emission bandwidth (ΔλP), stimulated emission cross section (σse) and gain bandwidth (σse × Δλp) were determined on the emission spectra, and the optimum doping concentration of Er2O3 was 0.5mol%. The present work indicates that Er3+/Yb3+ co-doped bismuth calcium borate glass can be promising materials for solid state NIR lasers and fiber amplifiers.

Combined Raman and autofluorescence ex vivo diagnostics of skin cancer in near-infrared and visible regions.

The differentiation of skin melanomas and basal cell carcinomas (BCCs) was demonstrated based on combined analysis of Raman and autofluorescence spectra stimulated by visible and NIR lasers. It was ex vivo tested on 39 melanomas and 40 BCCs. Six spectroscopic criteria utilizing information about alteration of melanin, porphyrins, flavins, lipids, and collagen content in tumor with a comparison to healthy skin were proposed. The measured correlation between the proposed criteria makes it possible to define weakly correlated criteria groups for discriminant analysis and principal components analysis application. It was shown that the accuracy of cancerous tissues classification reaches 97.3% for a combined 6-criteria multimodal algorithm, while the accuracy determined separately for each modality does not exceed 79%. The combined 6-D method is a rapid and reliable tool for malignant skin detection and classification.

Photochemical Treatment of Powder Coatings and VOC‐Free Coatings with NIR Lasers Exhibiting Line‐Shaped Focus: Physical and Chemical Solidification

AbstractNIR‐sensitized (NIR=near‐infrared) radical photopolymerization can be employed to chemically cure VOC‐free coatings; that is, either a powder coating or liquid monomer coating system with no significant components of volatile organic compounds (VOC). A NIR laser with line‐shaped focus was applied to cure the coatings. This system operated in multi‐wavelength mode where preferentially the emission wavelengths λ=808 nm and 980 nm of the laser system could be employed to solidify and crosslink the starting components as a transparent film; that is, chemical drying by photonic events. Cyanines absorbing at λ=980 nm and 808 nm functioned as heat generators to melt the powder and as sensitizers (Sens) to generate initiating radicals in combination with a radical initiator (RI). The radical initiator was either the iodonium salt RI‐1 ([(t‐C4H9‐Ph)2I+][(CF3SO2)2N−]) or triazine A (RI‐2). Photoinduced electron transfer between the excited states of Sens and RI was found to control the efficiency of initiating radicals. Line‐shape‐focused laser experiments demonstrated that both liquid VOC‐free coatings and solid powder coatings can be cured. Curing of solid powder coatings occurs with a curing rate of 3.6 m min−1, opening the possibility to introduce NIR laser curing as a new technology in coating sciences. Finally, rheological measurements and differential scanning calorimetry (DSC) were applied to characterize the flow properties of the molten powder and the glass transition temperatures of the crosslinked materials, respectively. The molten powder coating behaved like a liquid up to 160 °C as concluded from the complex shear modulus (G*), while the phase shift (∂) documents crosslinking above this temperature.

Spectroscopic investigations of Nd3+ doped gadolinium calcium silica borate glasses for the NIR emission at 1059 nm

The Nd3+-doped gadolinium calcium silica borate (BSGdCaNd) glasses of composition (55-x) B2O3 - 10 SiO2 - 25 Gd2O3 -10 CaO -x Nd2O3, where x = 0.0, 0.05, 0.5, 1.0, 1.5, 2.0 and 2.5 mol %, have been prepared by conventional melt quenching technique and are characterized through structural, thermal, absorption, emission and decay time measurements. Based on the Judd-Ofelt intensity parameters and radiative properties were determined from the absorption spectrum. The emission spectra recorded for BSGdCaNd glasses gives three emission transitions 4F3/2 → 4I9/2 (903 nm), 4F3/2 → 4I11/2 (1059 nm) and 4F3/2 → 4I13/2 (1334 nm) for which effective bandwidths (Δλeff) and stimulated emission cross-section (σ(λp)) are evaluated. Branching ratios (βR) measured for BSGdCaNd0.5 glass show that 4F3/2 → 4I11/2 transition is quite suitable for lasing applications. The intensity of emission spectra increases with increase in the concentration of Nd3+ ion up to 1.0 mol% and beyond that concentration, quenching is observed. The decay from 4F3/2 level is found to be non-exponential nature for concentrations of Nd3+ ions. The non-exponential curve has been fitted to the Inokuti-Hirayama model to understand the nature of energy transfer process. Hence, the high emission cross-section (1.39 × 10−20 cm2), branching ratio (0.58) and long lifetime (342 μs) indicate that the BSGdCaNd0.5 glass system could be considered as a good candidate for strong NIR lasers at 1059 nm.

The mechanism underlying calcium phosphate precipitation on titanium via ultraviolet, visible, and near infrared laser-assisted biomimetic process

We recently developed a rapid single-step calcium phosphate (CaP) precipitation technique on several substrates using a laser-assisted biomimetic process (LAB process). In this process, ultraviolet (UV, λ = 355 nm) pulsed laser irradiation has been applied to a substrate that is immersed in a supersaturated CaP solution. In the present study, the LAB process for CaP precipitation on a titanium substrate was successfully expanded to include not only UV but also visible (VIS, λ = 532 nm) and near infrared (NIR, λ = 1064 nm) lasers. Surface heating and plasma-mediated surface reactions (micro-deformation, oxidization, photoexcitation, and wetting) generated by UV, VIS, or NIR lasers are considered to be involved in the CaP precipitation on the titanium surface in the LAB process. The kinetics of these reactions and consequently of CaP precipitation were dependent on the laser wavelength and fluence. The higher laser fluence did not always accelerate CaP precipitation on the substrate; rather, it was found that an optimal range of fluence exists for each laser wavelength. These results suggest that for efficient CaP precipitation, a suitable laser wavelength should be selected according to the optical absorption properties of the substrate material and the laser fluence should also be adjusted to induce surface heating and plasma-mediated surface reactions that are favorable for CaP precipitation.

Energetic Chromophores: Low-Energy Laser Initiation in Explosive Fe(II) Tetrazine Complexes.

The synthesis and characterization of air stable Fe(II) coordination complexes with tetrazine and triazolo-tetrazine ligands and perchlorate counteranions have been achieved. Time-dependent density functional theory (TD-DFT) was used to model the structural, electrochemical, and optical properties of these materials. These compounds are secondary explosives that can be initiated with Nd:YAG laser light at lower energy thresholds than those of PETN. Furthermore, these Fe(II) tetrazine complexes have significantly lower sensitivity than PETN toward mechanical stimuli such as impact and friction. The lower threshold for laser initiation was achieved by altering the electronic properties of the ligand scaffold to tune the metal ligand charge transfer (MLCT) bands of these materials from the visible into the near-infrared region of the electromagnetic spectrum. Unprecedented decrease in both the laser initiation threshold and the mechanical sensitivity makes these materials the first explosives that are both safer to handle and easier to initiate than PETN with NIR lasers.

Luminescence spectral studies of Tm3+ ions doped Lead Tungsten Tellurite glasses for visible Red and NIR applications

Lead Tungsten Tellurite (LTT) glasses doped with different concentrations of Tm3+ ions of composition (60−x) TeO2+25WO3+15PbF2+xTm2O3 (Here x=0.1, 0.5, 1.0, 1.5, 2.0, 2.5mol%) were prepared by using melt quenching technique and characterized through optical absorption, photoluminescence and decay spectral studies to know the feasibility of using these glasses as luminescent devices in visible Red and NIR regions. Judd–Ofelt (J–O) theory has been applied to the optical absorption spectral profiles to calculate the J–O intensity parameters Ωλ (λ=2, 4 and 6) and consecutively used to evaluate various radiative properties such as radiative transition probability (AR), radiative lifetimes (τR) and branching ratios (βR) for the prominent luminescent levels. The luminescence spectra for all the LTT glass samples have two intense peaks in bright red and near Infrared regions at 650nm (1G4→3F4) and 800nm (3H4→3H6) respectively for which effective band widths (ΔλP), experimental branching ratios (βexp) and stimulated emission cross-sections (σse) are evaluated. The decay profiles for all the glasses are recorded to measure the quantum efficiency by coupling the radiative with experimental lifetimes. From the measured emission cross-sections, quantum efficiency and CIE chromaticity co-ordinates, it was found that 0.5mol% of Tm3+ ions doped LTT glass is most suitable for generating bright visible Red and NIR lasers to operate at 650 and 800nm respectively.

Optical properties of Nd3+-doped and Er3+–Yb3+ codoped borotellurite glass for use in NIR lasers and fiber amplifiers

The optical properties of borotellurite glasses doped with Nd3+ ions or codoped with Er3+–Yb3+ ions are investigated, in order to evaluate the potential application of these types of glass in laser systems and amplifier materials. The Judd–Ofelt (JO) model is used to determine the absorption intensities of both types of glass so as to establish the J–O intensity parameters (Ωλ). The J–O intensity parameters are then used to determine the various radiative parameters viz., the radiative transition probabilities (AR), branching ratios (βR), stimulated emission cross-sections (σe), full width half maxima (Δλp) and radiative lifetimes (τR) of both types of glass, which are also compared to the equivalent parameters for other host glasses. It has been shown that Yb3+ acts as an Er3+ sensitizer and contributes largely to the improvement of the spectroscopic properties of the glasses that is codoped with Er3+–Yb3+. The obtained values ofAR, βR, τR, σe and Δλp for the Nd3+- and Er3+-doped glass show that both the 4F3/2→4I11/2 transition at 1.06μm in the Nd3+ case and the 4I13/2→4I15/2 transition at 1.56μm for the Er3+ case exhibit better NIR luminescence at a level suitable for photonic device applications. The potential of the glasses examined in this study, due to their promising gain media, is also discussed in terms of the development of solid state NIR lasers and optical amplification for telecommunication applications.

High contrast laser marking of alumina

Alumina serves as raw material for a broad range of advanced ceramic products. These elements should usually be identified by some characters or symbols printed directly on them. In this sense, laser marking is an efficient, reliable and widely implemented process in industry. However, laser marking of alumina still leads to poor results since the process is not able to produce a dark mark, yielding bad contrast.In this paper, we present an experimental study on the process of marking alumina by three different lasers working in two wavelengths: 1064nm (Near-infrared) and 532nm (visible, green radiation). A colorimetric analysis has been carried out in order to compare the resulting marks and its contrast. The most suitable laser operating conditions were also defined and are reported here. Moreover, the physical process of marking by NIR lasers is discussed in detail. Field Emission Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy were also employed to analyze the results. Finally, we propose an explanation for the differences of the coloration induced under different atmospheres and laser parameters. We concluded that the atmosphere is the key parameter, being the inert one the best choice to produce the darkest marks.

Gold Nanorods: Near-Infrared Plasmonic Photothermal Conversion and Surface Coating

In this paper, AuNRs colloids with SPRL located at ~810 nm and ~1100 nm were synthesized using an improved seed method. Based on the NIR lasers available, photothermal conversion of AuNRs were systematically studied compared with that of water. Under low power irradiation, the highest temperature is obtained when the SPRL wavelength of AuNRs is equal to the laser wavelength, and temperature of colloid increases from ~20°C to ~65°C. With increasing laser power (such as 6 W), the AuNRs colloid boils within a few minutes, and nanorods undergo a shape deformation from rod to spherical particle and even fusion, and the SPRL disappears. For further investigation, the obtained AuNRs were coated with SiO2 shell to form a core-shell nanostructure (Au@SiO2). The surface coating can be used not only in keeping the stability of AuNRs for further treatment, but also in increasing plasmonic property and biocompatibility. This work will be useful for designing plasmonic photothermal properties and further applications in nanomedicine.

The Discrimination of Colored Acrylic, Cotton, and Wool Textile Fibers Using Micro‐Raman Spectroscopy. Part 1: In situ Detection and Characterization of Dyes

Raman spectroscopy has been applied to characterize fiber dyes and determine the discriminating ability of the method. Black, blue, and red acrylic, cotton, and wool samples were analyzed. Four excitation sources were used to obtain complementary responses in the case of fluorescent samples. Fibers that did not provide informative spectra using a given laser were usually detected using another wavelength. For any colored acrylic, the 633-nm laser did not provide Raman information. The 514-nm laser provided the highest discrimination for blue and black cotton, but half of the blue cottons produced noninformative spectra. The 830-nm laser exhibited the highest discrimination for red cotton. Both visible lasers provided the highest discrimination for black and blue wool, and NIR lasers produced remarkable separation for red and black wool. This study shows that the discriminating ability of Raman spectroscopy depends on the fiber type, color, and the laser wavelength.

Microstructure and Transport Properties of Bi-2212 Prepared by CO2 Laser Line Scanning

A novel Laser Line Scanning method has been applied to process rectangular cross-section Bi-2212 monoliths containing 2.9 % Ag using a CO2 Laser. Although previous work has suggested the use of nIR lasers (≈0.8–1.1 μm) for melt-processing metal oxide superconductors, the results obtained here demonstrate that mid-IR radiation from a CO2 laser (10.6 μm) may be just as convenient for such a purpose while it enables processing large surface areas. The samples described here were processed at traverse rates ranging between 15 and 60 mm/h, exhibited a complex textured microstructure and yielded highest Ic values of 71 A at 77 K.

Effects of γ-ray irradiation and thermal annealing on structural, optical and electrical properties of vacuum deposited vanadyl 2,3-naphthalocyanine thin films

Vacuum deposited vanadyl naphthalocyanine (VONc) crystalline thin films were produced. The films showed a completely different structural and growth pattern on thermal annealing and γ-ray irradiation. The XRD spectra revealed polycrystalline nature for both annealed and γ-ray irradiated films. Raman spectra observes that the γ-irradiated films had a higher disorder producing broad and diffuse peaks in comparison to its annealed samples. In the absorption spectra, the γ-irradiated films shows a broad Q-band with a shift of 50 nm towards the IR region enabling VONc to be used in a lot of applications using the commercially available semiconductor NIR lasers. Films on 97.9 krad γ-ray irradiation showed some interesting properties with a better conductivity compared to either it’s higher γ-ray irradiated counterpart (195.8 krad) or the annealed films. Also the activation energy values, which is the minimum amount of energy required to liberate charge carriers from traps or to ionize levels within the band gap, was found to be lowered to half of its value for the films irradiated at 97.9 krad promising its performance in optical data recording, photo-sensitizer in photodynamic therapy, etc.

Study The effect of central ion to the dithene complexes on spectral shifting of saturable absorber band

In this work dithine complexes prepared from dithiol benzil ligand and central ion to the Ni,Pd,Pt, element the ligand and complexes have been investigated using FTIR spectrophotometer and uv-vis-NIR spectral reigns show higher intensity represents the ?-?* transition in the chromopher cycle .These absorption which appear in visible and near IR spectral regions ,According to the complexes of one group ,the spectral shifting due to the change of central ion has been found to be related to atomic number of central ion .This shifting is increased while decreasing the central ion atom number These complexes have been implemented in Nd+2:YAG cavity because each posses resonant absorption band near Nd+2:YAG, Nd+2:Glass emitting at (1060nm). pulse duration measured to complexes dissolved in dioxin(2*10-3M) is very short compared with free running pulse duration ,therefore the complexes work as Q-switch to the NIR lasers.

Study The effect of central ion to the dithene complexes on spectral shifting of saturable absorber band

In this work dithine complexes prepared from dithiol benzil ligand and central ion to the Ni,Pd,Pt, element the ligand and complexes have been investigated using FTIR spectrophotometer and uv-vis-NIR spectral reigns show higher intensity represents the ?-?* transition in the chromopher cycle .These absorption which appear in visible and near IR spectral regions ,According to the complexes of one group ,the spectral shifting due to the change of central ion has been found to be related to atomic number of central ion .This shifting is increased while decreasing the central ion atom number These complexes have been implemented in Nd+2:YAG cavity because each posses resonant absorption band near Nd+2:YAG, Nd+2:Glass emitting at (1060nm). pulse duration measured to complexes dissolved in dioxin(2*10-3M) is very short compared with free running pulse duration ,therefore the complexes work as Q-switch to the NIR lasers.

Core@shell nanostructures for photothermal conversion: Tunable noble metal nanoshells on cross-linked polymer submicrospheres

Highly cross-linked and monodispersed poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) submicrospheres were synthesized by one-step polycondesation. The spheres are enriched in N, P, and S atoms, and phenolic hydroxyl groups, and exhibit good water dispersion. These properties facilitate initial growth of gold nanoseeds on the PZS surface and subsequent growth of gold nanoshells. This facile fabrication method can also be used for the preparation of silver and gold–silver bimetallic nanoshells with tunable thickness by varying the mass ratio of metal salt to PZS. The core@shell structures were investigated by transmission electron microscopy, energy-dispersive X-ray spectrometry, selected-area electron diffraction and X-ray diffraction analysis. PZS@gold nanoshells showed very strong surface plasmon resonance absorption in the near infrared region (700–1100 nm), where blood and biological tissues are nearly transparent. Furthermore, PZS@gold nanoshells effectively induced photothermal conversion under laser irradiation of 808 nm and rapidly killed tumor cells, suggesting potential application in photothermal imaging and therapies using NIR lasers.