CW Diode Laser Research Articles

Spectral Separation of Up-Conversion Luminescence Processes

Here, we present a novel method for the separation of overlapping emission spectral lines corresponding to nonlinear processes, which differ by effective nonlinearity with respect to the pump field power. The method exploits the factorization of wavelength and pumping power dependencies of the components processes contributions to the total luminescence. The advantage of our method is an ability to be self-testing and robust with respect to noise and experimental imperfections. We successfully demonstrate functionality of the method in the experiment with up-conversion luminescence of the fluorophosphate glass doped with rare-earth ions Yb3+ and Tm3+ pumped by 975 nm CW diode laser.

Luminescent and magnetic Y2O3: Er3+-Yb3+@γ-Fe2O3 bifunctional broadband emitting nanocomposites

The development of novel nanocomposites containing upconverting luminescent materials and magnetic nanoparticles have shown their potential applications in the hyperthermia and bio-imaging. In this regards, the search for new class of nanocomposites, which is responsive to magnetic and optical guiding in medical fields are in demand. To resolve the problem, bifunctional upconverting Y2O3: Er3+-Yb3+@γ-Fe2O3 nanocomposites have been synthesized through ball milling approach. Nanocomposites are able to upconvert NIR photons into overall yellowish-white colour broadband visible emission in 400–900 nm wavelength range at room temperature under 980 nm CW laser diode excitation. Thermal conductivity study shows an improved phonon scattering process in the Y2O3: Er3+-Yb3+@γ-Fe2O3 (∼ 0.0681 W/mK) nanocomposites as compared to Y2O3: Er3+-Yb3+ (∼ 0.0750 W/mK) phosphors due to grain boundary expansion. Broadband UC emission is originated via Yb-Yb dimer formation and heat associated continuum emission is reported due to photon avalanche (∼ 6 NIR photons) phenomenon. Besides, it also exhibits the attraction ability towards the magnet. Therefore, the developed nanocomposites can be used in converting the NIR radiation into broadband upconversion emission and luminescence imaging applications.

Electromagnetically induced transparency with magnetically induced ΔF=0,mF=0→mF=0 probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to |Fg=F,mF=0⟩→|Fe=F,mF=0⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.

Laser Produced Hydrophilic and Hydrophobic Silicon Surfaces

Two lasers were utilized for silicon processing using photoelectrochemical etching and laser texturing in order to produce nano/micro structures, respectively. Photoelectrochemical etching process utilizes a CW diode laser of 532 nm wavelength was used to support electrochemical etching for both n-type and p-type conductivity. While laser texturing process was employed using pulsed fiber laser of 1064 nm wavelength. Various characterization methods were devoted to examine silicon micro/nanostructures surfaces produced by lasers. These methods include AFM, SEM and Raman scattering to provide clear evidence about formation of micro/nanostructures abundant at silicon surfaces. Moreover, FTIR analysis for the laser produced silicon surfaces could emphasize whether the resultant silicon surface is hydrophilic or hydrophobic. Image analysis software adopted a side view micro image was used to measure the contact angle between the water droplet and silicon micro/nano-surfaces. It is found that the laser produced silicon nanostructure by photoelectrochemical etching creates a hydrophobic surface and even super hydrophobic with contact angle of 130 degrees for 50 nm average size. In addition, utilizing fiber laser of high repetition rate for laser texturing produces microstructures that are super hydrophilic with contact angle could reach 8 degrees for a surface dimension of 50 μm.

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode.

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages.

A new vision of photothermal therapy assisted with gold nanorods for the treatment of mammary cancers in adult female rats.

Over the past decade, the therapeutic landscape has markedly changed for patients with breast cancers (BCs), yet few studies have evaluated the power of the photothermal therapy (PTT) technique. The present study aimed to assess the potency of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary cancer treatment with this technique. In total, forty-two adult virgin female Wistar rats were categorized into seven groups, negative control, polyvinylpyrrolidone-capped gold nanorods (PVP-AuNRs) positive control (400 μL per rat ∼ 78 ppm), NIR laser irradiation 808 nm positive control with an intensity of (808 nm NIR CW diode laser, 200 mW cm-2 for 5 min), DMBA-treatment, DMBA-induced mammary cancer group treated with polyvinylpyrrolidone-capped gold nanorods, DMBA-induced mammary cancer group treated with NIR laser irradiation, and DMBA-induced mammary cancer group treated with polyvinylpyrrolidone-capped gold nanorods and NIR laser irradiation. Treatment with polyvinylpyrrolidone-capped gold nanorods and/or NIR laser irradiation was performed after three weeks of DMBA-induced mammary cancer. The mammary tumor lesions in the rat model induced with DMBA are highly invasive. Synthesis and characterization of gold nanorods (AuNRs) with an aspect ratio ranging from 2.8 to 3 were employed to validate the nanostructure and polyvinylpyrrolidone capping and their stability in absorbing near-infrared light. As a result, the therapy strategy, DMBA + PVP-AuNRs + NIR, effectively treated the tumor and halted its growth. The mammary glands were dissected and subjected to biochemical analysis for serum and tissue. Our treatment technique improved the histological aspects of mammary cancer in various forms of mammary cancer detected. Immuno-histochemical localization and TEM images supported these results reflecting the efficacy of this technique. Finally, our findings uncover for the first time the revolutionary effect of the PTT strategy using PVP-capped AuNRs in selectively destroying mammary cancer cells in rats.

A distributed-feedback grating excited by a CW laser diode for portable detection of explosive vapors with high sensitivity and stability

The practicality of non-contact detection of explosive vapors has always faced challenges in miniaturization, sensitivity, and stability.

Deciphering ethynyl single crystal for NLO applications: Synergistic studies on the structural, Hirshfeld surface, photophysical and DFT assessment

In this contribution, we have integrated multiple approaches in investigating the profiles and behaviour of simple ethynyl derivative, 1-[4-(4-(dimethylaminophenyl)ethynyl)phenyl]ethanone (4DME) tolane which is known to be integrated widely in molecular electronics as conjugated building block in functional molecules. Prepared via simplified aerobic Sonogashira cross-couping reaction, symmetrical chromophore of 4DME crystallizes in monoclinic with complex framework containing the space group of P21/n and includes four molecules within a unit cell. The fingerprint plots and Hirshfeld surface analyses demonstrate the presence of synergism between molecules supporting nonlinear optical response of the compound. It was shown that C⋯H contact (44.5 %) is the major contribution of intermolecular interaction executed by Hirshfeld surface area. The investigation on their spectroscopic, thermal analysis and density functional theory (DFT) analysis operating under B3LYP/6-31G (d,p) were conducted to determine the energies of the LUMO and HOMO level, NLO behaviour, intermolecular charge transport facilitated by global chemical reactivity descriptors, molecular electrostatic potentials (MEP) and hyperpolarizability analyses. From the simulated DFT calculation, it shows that 4DME has good polarizability properties with HOMO-LUMO energy gap of 3.89 eV. Calculated total first hyperpolarizability βtot of 4DME were 1261.40 × 10−30 esu which can be potentially applied as good nonlinear optical materials. The preliminary outcomes prove that this simple ethynyl derivative is capable of being used in optoelectronic industry as NLO-based products. A CW diode laser operating at 532 nm wavelength was used to perform the Z-scan measurements and 4DME showed an effective value of χ(3) in order of 10−6, indicating good nonlinear properties.

High-resolution 3D nanoprinting based on two-step absorption via an integrated fiber-coupled laser diode.

Three-dimensional (3D) laser nanoprinting with high resolution and low cost is highly desirable for fabricating arbitrary 3D structures with fine feature size. In this work, we use a 405-nm integrated fiber-coupled continuous wave (cw) laser diode to establish an easy-to-build 3D nanoprinting system based on two-step absorption. Two-dimensional (2D) gratings with a sub-150-nm period and 3D woodpile nanostructures with a lateral period of 350 nm have been printed at a low speed. At a faster scan velocity of 1000 µm/s, 2D gratings with sub-200-nm resolution and sub-50-nm linewidth can still be fabricated with laser power less than 1 mW. The two-step absorption of the used benzil initiator enables us to use a second cw laser with 532-nm wavelength to enhance the polymerization with sub-100-nm feature size when starting with insufficient 405-nm laser power, which possess the potential to find applications in high-speed high-resolution parallel-writing and in situ manipulation.

Temperature sensing based on upconversion properties of Yb3+/Ho3+/Tm3+ tri-doped Y2O3 micro particles phosphors obtained by conventional precipitation method

Upconverter materials based on Y0.983-xYb0.012Ho0.005TmxO3, x = 0.000 – 0.012, were synthesized by conventional coprecipitation method followed by calcination process at different temperatures: 900, 1000, and 1100 °C for 4 h under air atmosphere. The materials were characterized by XRD, SEM, and PL. The effects of the dopant concentration and calcination temperature on the upconversion emission quantum yield were investigated upon excitation with CW laser diode at 980 nm, with tunable laser power pump. Predominant emission narrow bands arising from Ho3+ transitions (5F4,5S2→5I8) in the green region and Tm3+ (1G4→3H6) in the blue spectral region, and (3H4 → 4H6) in the infrared region, were observed. The material containing Yb3+, Ho3+ presented values of relative sensitivity (SR) from 1.3 K−1 (13 K) to 0.00119 K−1 (450 K) while the presence of the Yb3+, Ho3+, and Tm3+ in material exhibited 1.2 K−1 (13 K) to 0.00097 K−1 (450 K). The system showed emission via upconversion mechanism, even suspended in aqueous medium. Furthermore, the concentration of Tm3+ showed to be crucial for the change in the upconversion intensity of the present materials. These outcomes strongly suggest that the tri-doped Ho3+, Yb3+, and Tm3+ materials discussed here may be suitable for optical temperature sensing and PDT.

High-flux, high-visibility entangled photon source obtained with a non-collinear type-II PPKTP crystal pumped by a broadband continuous-wave diode laser

We demonstrated a high-brightness, polarization-entangled bi-photon source generated in a type-II phase-matched non-collinear PPKTP crystal pumped by a 405 nm continuous-wave (cw) broadband diode laser. Basing on the single-pass configuration, we investigated the distribution characteristics of the bi-photon cone and the wavelength tunability with crystal temperatures. Overcoming the degradation of the bi-photon generation rate and the spectral correlation induced by the broadband pump laser, we obtained a bi-photon generation rate of 7.48×103/s/mW/nm and an interference visibility over 95% via a Hong–Ou–Mandel (HOM) configuration. We established a theoretical model to address the bi-photon time-delayed HOM dip pumped by the broadband cw diode laser in spontaneous parametric down-conversion and obtained the complete analytic solution of the bi-photon coincidence counting rates.

Direct frequency domain fluorescence lifetime imaging using simultaneous ultraviolet and visible excitation.

Due to the complexity, limited practicality, and cost of conventional fluorescence lifetime imaging/microscopy (FLIM) instrumentation, FLIM adoption has been mostly limited to academic settings. We present a novel point scanning frequency-domain (FD) FLIM instrumentation design capable of simultaneous multi-wavelength excitation, simultaneous multispectral detection, and sub-nanosecond to nanosecond fluorescence lifetime estimation. Fluorescence excitation is implemented using intensity-modulated CW diode lasers that are available in a selection of wavelengths spanning the UV-VI-NIR range (375-1064 nm). Digital laser intensity modulation was adopted to enable simultaneous frequency interrogation at the fundamental frequency and corresponding harmonics. Time-resolved fluorescence detection is implemented using low-cost, fixed-gain, narrow bandwidth (100 MHz) avalanche photodiodes, thus, enabling cost-effective fluorescence lifetime measurements at multiple emission spectral bands simultaneously. Synchronized laser modulation and fluorescence signal digitization (250 MHz) is implemented using a common field-programmable gate array (FPGA). This synchronization reduces temporal jitter, which simplifies instrumentation, system calibration, and data processing. The FPGA also allows for the implementation of the real-time processing of the fluorescence emission phase and modulation at up to 13 modulation frequencies (processing rate matching the sampling rate of 250 MHz). Rigorous validation experiments have demonstrated the capabilities of this novel FD-FLIM implementation to accurately measure fluorescence lifetimes in the range of 0.5-12 ns. In vivo endogenous, dual-excitation (375nm/445nm), multispectral (four bands) FD-FLIM imaging of human skin and oral mucosa at 12.5 kHz pixel rate and room-light conditions was also successfully demonstrated. This versatile, simple, compact, and cost-effective FD-FLIM implementation will facilitate the clinical translation of FLIM imaging and microscopy.

Low-power laser manufacturing of copper tracks on 3D printed geometry using liquid polyimide coating.

Silver nanoparticle photoreduction synthesis by direct laser writing is a process that enables copper micro-track production on very specific polymers. However, some important 3D printing polymers, such as acrylonitrile butadiene styrene (ABS) and acrylates, do not accept this treatment on their surface. This work presents an approach to produce copper microcircuitry on 3D substrates from these materials by using direct laser writing at low power (32 mW CW diode laser). We show that by coating a thin layer of polyimide (PI) on a 3D-printed geometry, followed by a sequence of chemical treatments and low-power laser-induced photoreduction, copper tracks can be produced using silver as catalyst. The surface chemistry of the layer through the different stages of the process is monitored by FTIR and X-ray photoelectron spectroscopy. The copper tracks are selectively grown on the laser-patterned areas by electroless copper deposition, with conductivity (1.2 ± 0.7) × 107 S m-1 and a width as small as 28 μm. The patterns can be written on 3D structures and even inside cavities. The technique is demonstrated by integrating different circuits, including a LED circuit on 3D printed photopolymer acrylate and a perovskite solar cell on an ABS 3D curved geometry.

Effect of thermoelastic stresses on radiation spectra of CW laser diode bars

Detailed measurements of radiation spectra of individual emitters in CW laser diode bars (LDBs) were done. For the first time, the anomalies in the measured spectral distributions over the emitting apertures were observed, which can not be explained through consideration of measured and modeled relatively smooth temperature distributions over the LDBs. Explanation of these spectral features in the measured spectral distributions along LDBs has been achieved with numerical modeling of not only the temperature profiles but also thermo-elastic stress in LDBs that can strongly affect the radiation characteristics of emitters. Three main mechanisms of the thermo-elastic stresses occurrence in operating LDBs have been considered: “initial” stresses in an unbounded bar, stresses as a result of the assembling process, and stresses as results of working regime of LDB. Understanding of demonstrated experimentally and theoretically effect of thermo-elastic stresses on spectral behavior of emitters in LDBs will promote development of new generation of high-power laser systems, in particular, with beam summation via spectral combining method.

Aggregation-induced upconversion enhancement and application based on rhodamine derivatives

In this work, we firstly report that one-photon absorption-based upconversion (oPUC) exhibits aggregation-induced emission enhancement (AIEE) based on rhodamine chromophores. Under excitation of 655 nm CW diode laser, the maximum upconversion intensity presents ∼27-fold increase in the concentration range of 1 μM–1 mM (while the Stokes fluorescence has already completely quenched at this moment). It was demonstrated that such AIEE feature is attributed to the upconversion radiative decay being activated in the more concentrated solution. A turn-on chemsensor rhodamine thiospirolactone (RhS) was synthesized for the application. The results demonstrated that the oPUC detection with AIEE feature can probe Hg2+ in the range as wide as 0–1.0 mM, showing the potential application of this upconversion detection in the large concentration and wide range ion probing.

Synthesis, crystal structure, characterization, Hirshfeld analysis, molecular docking and DFT calculations of 5-Phenylamino-isophthalic acid: A good NLO material

5-Phenylamino-isophthalic acid (H2L) (C15H13NO4) has been synthesized, characterized via single-crystal X-ray diffraction, spectroscopic techniques and also studied theoretically using DFT approach. The compound crystallizes in a monoclinic crystal system with a P21/c space group with Z = 2 and the following unit cell dimensions: a = 10.4415(14) Å, b = 16.472(2) Å, c = 7.5305(10) Å. DFT calculations were carried out by B3LYP/6–311++G(d,p) level and geometry optimization, vibrational analysis, MEP, ELF, NBO, NHO, and FMO analysis were also carried out. The calculated values showed excellent agreement with the experimental data. The vibrational frequencies were evaluated using density functional theory (DFT) with the complete PED analysis. The Molecular Frontiers Orbitals (FMO) or HOMO/LUMO energy values showed that there wasa satisfying interchange of charge occurring within the molecule. Hirshfeld surface analysis was carried out to study 3-D and 2-D interactions in crystal. Molecular docking was done with 4 protein receptors to find the best ligand-protein interactions. The nonlinear optical characteristics of the title compound have been evaluated using the Z-scan method with CW diode laser working at 520 nm. The third-order nonlinear refraction coefficient (n2), nonlinear absorption (β), nonlinear susceptibility χ(3), and second-order hyperpolarizability (γ) are of the order of 10−8 cm2/ W, 10−3 cm/ W, 10−7 esu, and 10−27 esu, respectively.

Synthesis and nonlinear optical study of the hybrid salt: [C12H14N2][Fe(CN)5(NO)]⋅5H2O

The new prepared hybrid salt 1,1’-(Ethylene-1,2-diyl)dipyridinium pentacyanidonitrosoferrate(II) pentahydrate was synthesized. Then, it was characterized using different spectroscopic methods. The nonlinear optical properties of the new compound were investigated using the simple [Formula: see text]-scan technique with a CW diode laser radiation ([Formula: see text][Formula: see text]nm). Also, the [Formula: see text]-scan technique with pump/probe configuration was utilized to observe the Cross Phase Modulation (XPM) phenomena. Theoretical fit to the new experimental data was performed to calculate the third order nonlinear optical parameters including the nonlinear refractive index, which is about [Formula: see text][Formula: see text]cm2/W. This kind of molecule is considered to be promising candidate for using in future optoelectronic devices.

Quantification of the effectivity of laser therapy shortly following brain injury via dual-wavelength laser imaging

Treatment of traumatic brain injury, within a few minutes and even before transportation to the nearest medical facility, can significantly curtail injury severity and even prevent death. The primary aim of this study was to evaluate the effect of laser irradiation as a therapeutic intervention tool immediately following brain injury. To this end, a dual-wavelength laser speckle contrast imaging (DW-LSCI) system based on two laser sources at two wavelengths 532 and 660 nm was employed to monitor changes in cerebral blood flow, tissue saturation and rate of oxygen consumption in a mouse model of intact head injury. In addition, structural changes of tissue were evaluated using linear approximation to Rayleigh-MIE scattering in the range between the two laser wavelengths. Furthermore, cerebral tissue temperature was imaged by a thermal camera providing additional information on physiological brain tissue condition. Experiments were conducted on anesthetized mice (n = 6, female) subjected to a closed head weight-drop model of focal brain injury. After 5 min of baseline measurement, focal brain injury was induced and measurements were conducted for 10 min. Low-level laser therapy (LLLT) was than administrated for a duration of 15 min with uniform exposure of 45 J/cm2 from a CW diode laser source (810 nm). Concurrently, measurements were carried out over the treatment time interval. Laser illumination was then blocked and measurements continued for another 20 min, followed by euthanasia. In comparison to baseline measurements, noticeable variations were revealed post-injury which indicate the severity of brain damage. The use of LLLT inhibited the development of complications in the injured mice by increasing blood flow and saturation and overall oxygen consumption level over the injured area which highlights its effectiveness as a neuroprotective agent immediately following brain injury. Different doses of low-level laser irradiation were also tested (n = 12) with less effectiveness on cerebral parameters. The results presented here support our hypothesis that a high dose of laser irradiation as a first aid can attenuate the injury and save the brain from further worse outcome. To the best of our knowledge, the implementation of the DW-LSCI system to monitor brain hemodynamic and metabolic response to LLLT shortly after head injury in intact mouse brain has not been previously reported.

Experimental and computational investigation of novel dihydrated organic single crystal of 2,4,6-triaminopyrimidine and 3,5-dintrobenzoic acid: Linear and nonlinear optical response with limiting performance

Newly synthesized dihydrated organic crystal (TAP+DNB−.2H2O) of 2,4,6-triaminopyrimidine (TAP) with 3,5-dinitrobenzoic acid (DNB) was grown by slow evaporation technique and this crystal belongs to monoclinic P-1 space group. Infrared spectroscopy combined with DFT calculation has been used to confirm the presence of the expected functional group of the titular crystal. Further, the UV–Vis absorption spectroscopy has been utilized to determine various optical parameters such as excitation wavelength, optical band gap, and extinction coefficient from the point of view of optical application. In addition to this, TD-DFT/B3LYP computational theory was also applied to simulate the UV–Vis absorption spectrum for supporting the experimental result. The effect of complex formation from its constituents has been explored using frontier molecular orbitals analysis. Furthermore, the mapping of the 3D Hirshfeld surface and its related fingerprint plots were used for qualitative and quantitative analysis of the intermolecular interactions which involve among different molecular moiety in the synthesized crystal. The third-order nonlinear optical response of this molecular complex (TAP+DNB−.2H2O) have been investigated in detail using the z-scan technique with CW diode laser (520 ​nm). Also, theoretical nonlinear optical parameters have been investigated by the DFT method. The thermal characteristic of the growth dihydrate crystal has been studied by thermal gravimetric-differential thermal analysis (TG-DTA).

Numerical simulation of a laser with a Q-switched cavity for production of ultrashort pulses

A theoretical model was developed to calculate lasing modes for giant pulses in solid-state lasers with Q-switched cavities. The lasing process begins with steady-state mode locking. Then, when a control pulse is fed to the cavity electro-optic modulator, the light propagating in the cavity is amplified. When the laser pulse reaches maximum energy, the cavity opens, producing a single ultrashort pulse. Simulations performed using a commercial 50 W Nd:YAG solid-state CW laser diode pump module indicated that, when the driver parameters for the electro-optical modulator are optimized, the cavity switching mode can be used for high-efficiency extraction of almost all the energy (up to 20 mJ) stored in the laser medium in steady-state mode in the form of a single pulse with a duration in the hundreds of picoseconds.