Continuous Wave Diode Laser Research Articles

The Influence of Diode Laser Intensity Modulation on Photoacoustic Image Quality for Oral Soft Tissue Imaging.

Introduction: Imaging technologies have been developed to assist physicians and dentists in detecting various diseases. Photoacoustic imaging (PAI) is a new technique that shows great applicability to soft tissues. This study aimed to investigate the effect of diode laser intensity modulation on photoacoustic (PA) image quality. Methods: The prototype of the PAI system in this study utilized a non-ionizing 532 nm continuouswave (CW) diode laser illumination. Samples in this study were oral soft tissues of Sprague-Dawley rats fixed in 10% formalin solution. PA images were taken ex vivo by using the PAI system. The laser exposure for oral soft tissue imaging was set in various duty cycles (16%, 24%, 31%, 39%, and 47%). The samples were embedded in paraffin, and PA images were taken from the paraffinembedded tissue blocks in a similar method by using duty cycles of 40%, 45%, 50%, 55%, 60% respectively to reveal the influence of the laser duty cycle on PA image quality. Results: The oral soft tissue is clearly shown as a yellow to red area in PA images, whereas the nonbiological material appears as a blue background. The color of the PA image is determined by the PA intensity. Hence, the PA intensity of oral soft tissue was generally higher than that of the nonbiological material around it. The Kruskal-Wallis test followed by Mann-Whitney post-hoc analysis revealed significant differences (P<0.05) in the quality of PA images produced by using a 16%-47% duty cycle of laser intensity modulation for direct imaging of oral soft tissue fixed in 10% formalin solution. The PA image quality of paraffin-embedded tissue was higher than that of direct oral soft tissue images, but no significant differences in PA image quality were found between the groups. Conclusion: The PAI system built in this study can image oral soft tissue. The sample preparation and the diode laser intensity modulation may influence the PA image quality for oral soft tissue imaging. Nonetheless, the influence of diode laser intensity modulation is not significant for the PA image quality of paraffin-embedded tissue.

Smart YPO4:Er–Yb Nanophosphor for Optical Heating, Hyperthermia, Security Ink, Cancer Endoradiotherapy, and Uranyl Recovery

A YPO4:Er3+–Yb3+ nanophosphor has been synthesized by a facile coprecipitation method. The photon upconversion has been carried out at 980 nm continuous-wave laser diode excitation. Optical heating...

Low-cost single-point optoacoustic sensor for spectroscopic measurement of local vascular oxygenation.

Optical sensors developed for the assessment of oxygen in tissue microvasculature, such as those based on near-infrared spectroscopy, are limited in application by light scattering. Optoacoustic methods are insensitive to light scattering, and therefore, they can provide higher specificity and accuracy when quantifying local vascular oxygenation. However, currently, to the best of our knowledge, there is no low-cost, single point, optoacoustic sensor for the dedicated measurement of oxygen saturation in tissue microvasculature. This work introduces a spectroscopic optoacoustic sensor (SPOAS) for the non-invasive measurement of local vascular oxygenation in real time. SPOAS employs continuous wave laser diodes and measures at a single point, which makes it low-cost and portable. The SPOAS performance was benchmarked using blood phantoms, and it showed excellent linear correlation (R2=0.98) with a blood gas analyzer. Subsequent measurements of local vascular oxygenation in living mice during an oxygen stress test correlated well with simultaneous readings from a reference instrument.

A 27-W continuous-wave fiber-coupled green diode laser based on TO-can-packaged emitters

In this paper, we demonstrate a fiber-coupled green laser module based on multiple 1-W continuous-wave TO-can-packaged green laser diodes (LDs). Theoretically, we calculated the maximum number of the LDs that can be incoherently combined and effectively coupled into a given optical fiber using spatial and polarization beam combination technologies. Experimentally, we combined as many as 40 collimated green LDs and then coupled the combined beam into an optical fiber with a core diameter of 200-μm and a numerical aperture (NA) of 0.22. The coupling efficiency is as high as 94 % and a total output power of 27.6-W can be obtained, which corresponds to an electro-optic efficiency of 9.8 %.

Modelling Neural Dynamics with Optics: A New Approach to Simulate Spiking Neurons through an Asynchronous Laser

In this paper, we propose a novel approach for implementing spiking neurons through an optical system. Spiking neurons are a new approach to emulate the neural processes that occur in the brain, known as the third generation of artificial neural networks. They have been successfully used to build a new technology called neuromorphic engineering, which looks for a better performance than traditional computing in tasks usually performed by AI-based systems. Our optical system consists of a low-cost laser source, based on a microcontroller and a continuous-wave laser diode; the microcontroller allows producing synchronous or asynchronous pulses with complex time profiles. Here, through said system we have successfully reproduced most of the neural dynamics observed in biological neurons. These dynamics have been reproduced using a very simple optical array with a great potential for the development of neuromorphic systems. The optical system has been experimentally validated.

Vibrational spectroscopic, linear and nonlinear optical characteristics of Anthocyanin extracted from blueberry

A natural pigment Anthocyanin, extracted from blueberry, has been reported in this paper. The structure of blueberry powder was studied by X-ray diffraction (XRD) and it divulges that the prepared powder seems to be amorphous. Fourier transform infrared (FT-IR) and FT-Raman studies were carried out to recognize the functional groups present in Anthocyanin pigment. Third-order nonlinear optical characteristics of Anthocyanin have been measured using Z-scan technique with a continuous wave diode laser working at the excitation wavelength of 635 nm. Anthocyanin pigment exhibits a negative nonlinear index of refraction and absorption coefficient respectively due to self-defocusing and saturable absorption nature. The nonlinear index of refraction (n2) and nonlinear absorption coefficient (β) of Anthocyanin were measured to be −2.07 × 10−7 cm2/W and −2.19 × 10−3 cm/W respectively. Optical limiting (OL) of Anthocyanin was studied and this exhibits a low limiting threshold of 3.21 × 102 W/cm2. Figure of merit (FOM) conditions were verified for all-optical switching device applications. The present experimental results suggest that the natural pigment Anthocyanin may be a promising material for photonics and optoelectronics applications.

Influence of Al2O3 on the photoluminescence and optical gain performance of Nd3+ doped germanate and tellurite glasses

Abstract We investigated the influence of aluminum oxide, Al2O3, on the photoluminescence (PL) spectrum and optical gain (at 1064 m) of neodymium ion, Nd3+, doped tellurium and germanium oxide glasses with compositions TeO2 − ZnO and GeO2 − PbO, respectively. The PL properties of both materials were studied using a continuous-wave diode laser operating at 808 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. For samples containing Al2O3 it was observed PL intensity growth up to 30% in comparison with the samples without Al2O3. Luminescence decay (τm) from the 4F3/2 level was measured monitoring the 4F/32 → 4I11/2 transition. From calculations of the Judd–Ofelt parameters, the radiative lifetimes, the emission cross -section (σem) and the quantum efficiency of 4F3/2 → 4I11/2 transition were determined; the effective linewidth (Δλeff) was calculated to determine the gain bandwidth product (σem x Δeff), figure of merit (σem x τm) and saturation intensity (Is) parameters. Optical gain measurements were performed using a pump laser at 808 nm and a probe laser at 1064 nm. For the samples with Al2O3 the relative gain at 1064 nm reached ≈ 2.8 dB/cm (pump laser power: 400 mW) indicating an enhancement of about 65% for TeO2 − ZnO and 120% for GeO2 − PbO with respect to the samples without Al2O3. The optical gain enhancement is correlated to the PL intensity behavior and increases due to the presence of Al2O3 because the coordination environment of the Nd3+ changes and become more asymmetric leading to the growth of the emission cross-section. The present study shows that Nd3+ doped tellurium and germanium oxide glasses containing Al2O3 present particularly good prospects to be used as optical amplifiers at 1064 nm.

Solvent Dependent Linear and Nonlinear Optical Characteristics of Acid Blue 3 Dye.

The polar solvents dependent linear and third-order nonlinear optical (NLO) characteristics of acid blue 3 (AB 3) dye has beenreportedinthis paper. A low power continuous wave (CW) diode laser working at 635nm wavelength was used to perform the Z-scan experiments in the presentstudy. AB 3 dye was dissolved with different polar solvents of 1-propanol, ethanol, dimethyl sulfonate (DMSO) and water at a concentration of 0.01mM. The nonlinear index of refraction (n2) of AB 3 dye was ascribed to self-defocusing effect, and nonlinear coefficient of absorption (β) signifies the behaviors of saturable and reverse saturable absorption. The real and imaginary components of the third-orderNLO susceptibility of AB 3 dye in the presentpolar solvents have been measured to be ofthe order of 10─6 esu. The influence of polar solvents on third-orderNLO susceptibility of the dye sample studied has beendiscussed. The second-order hyperpolarizability (γ) of AB 3 dye has also been studied andestimated to be ofthe order of10─30 esu. The experimental results suggest that AB 3 dye may bea promising candidate for applications in nonlinear optics.

Formation of single-crystal Cu2O strips in non-single-crystal CuO thin films by continuous-wave laser diode with micro-chevron laser beam ($$\mu$$-CLB)

Crystallization of thin film materials by exploiting laser induced crystallization has been advancing for the past four decades. This unique thin film technique has been predominantly used in processing thin film materials made of a single chemical element; however, harnessing this technique to extend its use for thin film materials containing multiple chemical elements (e.g., metal oxides) unlocks applications currently not accessible. In this study, laser crystallization of a Cu2O strip was demonstrated. A continuous-wave laser diode with a micrometer-scale chevron-shaped beam profile (micro chevron laser beam) was used to crystallize CuO thin films covered with an amorphous carbon (a-C) cap layer, deposited on fused silica substrates. Electron backscatter diffraction, Raman spectroscopy, photoluminescence spectroscopy, and UV-Vis spectroscopy were used to investigate the crystallinity and optical properties of the Cu2O thin films revealing their unique characteristics associated with the crystallization process.

Effects of Rose Bengal‐ and Methylene Blue‐Mediated Potassium Iodide‐Potentiated Photodynamic Therapy on Enterococcus faecalis: A Comparative Study

This study was performed to compare the use of methylene blue (MB) and rose bengal (RB) in antimicrobial photodynamic therapy (PDT) targeting Enterococcus faecalis (E. faecalis) bacteria in planktonic and biofilm forms with potassium iodide (KI) potentiation. E. faecalis bacteria in planktonic form were exposed to antimicrobial PDT protocols activating MB and RB, with or without KI potentiation, following laser irradiation with different exposure times, 60 mW/cm2 laser power, and different photosensitizer agent (PS)/potentiator concentrations to observe relationships among the variables. Two continuous-wave diode lasers were used for irradiation (red light: λ = 660 nm and green light: λ = 565 nm). The pre-irradiation time was 10 minutes. The vitality of E. faecalis biofilm was assessed by confocal laser scanning microscopy, and the morphology was determined by scanning electron microscopy. The effects on the proliferation of stem cells from the apical papilla (SCAPs) were analyzed by cell counting kit-8 assay. The staining effect of antimicrobial PDT on dentin slices was investigated. Statistical analysis using a one-way analysis of variance was done. KI-potentiated RB and MB antimicrobial PDT both effectively eradicated E. faecalis bacteria in planktonic and biofilm forms. The minimum bactericidal concentrations of PSs (±100 mM KI) were obtained through PDT on planktonic E. faecalis, and the optimal light parameters were 60 mW/cm2 , 6 J/cm2 for 100 seconds. KI-potentiated PDT effectively strengthened the ability to inhibit E. faecalis biofilm with 86.50 ± 5.78% for MB (P = 0.0015 < 0.01) and 91.50 ± 1.75% for RB (P = 0.0418 < 0.05) of bactericidal rate, with less toxicity for SCAPs (P < 0.001) and less staining. KI could reduce the staining induced by antimicrobial PDT on dentin slices. A combination of KI and antimicrobial PDT may be a useful alternative to conventional disinfection methods in endodontic treatment. MB and RB antimicrobial PDT at much lower concentrations with KI could hopefully achieve disinfection effects comparable with those of 1.5% NaClO while causing few adverse effects on SCAPs. KI helps to avoid staining problems associated with high concentrations of photosensitizer agents. Lasers Surg. Med. © 2020 Wiley Periodicals, LLC.

Trivalent lanthanide doped orthovanadate phosphors for efficient upconversion

Lanthanide doped crystalline materials has gathered an immense impression to develop highly efficient upconverting phosphors for industrial as well as biomedical applications. The interaction between the electron cloud of the lanthanides and the crystal field of different host matrices affects the transition probabilities between the energy levels of lanthanide ions. Here, we have investigated the structural and optical properties of Er3+ doped YVO4 phosphors with the irradiation of 980 nm continuous wave diode laser. A twin efficient green band peaking at ∼ 525 nm and ∼ 554 nm has been observed along with a relatively low intense red band at ∼ 660 nm. The radiative/non radiative transitions between energy levels of Er3+ ions are well understood with the help of energy level diagram. The pump photons required to populate the green and red levels have been calculated. The colour coordinate of the prepared phosphors has been calculated by CIE chromaticity diagram. The present lanthanide-based phosphors have an efficient and bright upconversion emission, with applications spanning optical sensing, biological imaging, solid state lighting and LEDs.

Sub-ppb level detection of nitrogen dioxide based on an optimized H-type longitudinal acoustic resonator and a lock-in white-light interferometry demodulation algorithm

This paper presents an optimized H-type longitudinal resonant photoacoustic (PA) cell for nitrogen dioxide (NO2) gas detection. The PA field distributions of the H-type resonant PA cell have been evaluated to optimize the construction of the H-type resonant PA cell, using the finite element method and thermoviscous acoustic theory. The optimized H-type resonant PA cell, together with a high-power continuous-wave (CW) multimode laser diode emitting at around ~ 450 nm and a fiber-optic Fabry-Perot (F-P) acoustic sensor, constitutes a PAS system for NO2 detection. The dynamic cavity length of the fiber-optic acoustic sensor is demodulated by the lock-in white-light interferometry (WLI) demodulation algorithm. Experimental results show that the PA signals are proportional to the concentrations of NO2 for the range of 0-2 ppm (parts per million). The sensitivity is measured to be 0.652 nm/ppm and the minimum detectable limit of NO2 is calculated to be 1.26 ppb (parts per billion).

(Invited) Lanthanide Doped Nanoparticles and Their Applications

Since approximately 2000, lanthanide doped nanoparticles have received significant attention due to their interesting luminescent properties. At the core of this interest is their ability to convert near-infrared excitation light (typically 980 or 800 nm) to higher energies spanning the ultraviolet, visible and near-infrared regions of the spectrum through a multiphoton process known as upconversion. Upconversion differs from conventional multiphoton excitation in other materials where no real intermediate states are present necessitating the use of ultrafast lasers (in the femtosecond regime) for simultaneous excitation to the upper emitting state. The lanthanide ions possess a multitude of 4f electronic states that have long lifetimes (micro- to millisecond) thus act as population reservoirs in the upconversion process. Hence, upconversion occurs through real, long-lived intermediate states through a sequential photon absorption process. This eliminates the need for ultrafast excitation and as a result, upconversion can be observed using inexpensive, continuous wave diode lasers. Upconversion luminescence can be exploited for a number of applications in nanomedicine, theranostics, photovoltaics, photocatalysis, as well as many others.While their upconversion luminescence has been studied in great detail, lanthanide doped nanoparticles can also emit in the near-infrared through a direct Stokes (down-shifted) luminescence process. Of particular importance is that these near-infrared emissions lie within the biological windows where biological tissues are optically transparent. For obvious reasons, a great deal of the work on the nanomedicine and theranostics applications of lanthanide doped nanoparticles has shifted to their near-infrared luminescence properties.In this presentation, we will demonstrate the synthesis of these nanoparticles, establish how changing their nanoscale architecture can affect their luminescence properties (both upconversion and near-infrared), and discuss their potential applications, particularly in nanomedicine.

Temperature sensor based on IR-laser reduced Graphene Oxide

A simple, cost-effective approach to realize a sensitive temperature sensor based on IR laser reduced graphene oxide (IRLrGO) is reported. The sensor has been obtained by irradiating a graphene oxide (GO) film, placed between two thin glass substrates, with a continuous wave diode laser operating at 970 nm along its entire length. A conductive strip, 13 mm long, 300 μm wide and 7 μm thick, has been generated by moving the GO film on an X-Y translator stage with a given velocity with respect to the fixed laser fiber tip position. The laser treatment has given rise to the GO reduction confirmed by the resistance R measurements as well as from SEM, EDX, ATR-FTIR and Raman analyses. The temperature dependence of the conductive strip resistance has been measured in air from 30̂C to 80̂C and in high vacuum from 80 K to 300 K. The sample acts as a sensitive and low mass Resistance Temperature Detector (RTD). Such a sensor is biocompatible and requires a very low bias (<1 V). While the performances of the IRLrGO temperature sensor are stable under high vacuum conditions at room temperature, its behavior remains to be studied when it operates under different environmental conditions.

Characterisation and comparison of micropatterns written using a proton beam in Ag-activated glass and LiF crystal observed by single- and multi-photon microscopy

We investigate the characterisation and comparison of micro-scale patterns in silver-activated phosphate glass and lithium fluoride (LiF) single crystal written by a proton beam with an energy range of 1.7–4.5 MeV. A variety of micro-scale structures based on blue and orange luminescent Ag-related colour centres in Ag-activated glass and green and red luminescent F-aggregated colour centres in LiF are visualised by combining single- and two-photon confocal microscopes equipped with a blue continuous wave (cw) laser diode and a femtosecond (fs) laser in the near-infrared (NIR) region, respectively. Two- and three-dimensional (2D and 3D) reconstructed images are analytically evaluated using lateral/axial RPL intensity mapping. In addition, the origins of different RPL intensity profiles in a plateau region along the axial direction in both materials are examined and discussed.

Small-animal 360-deg fluorescence diffuse optical tomography using structural prior information from ultrasound imaging

.We demonstrate dual modality of free-space fluorescence diffuse optical tomography (FDOT) and handheld ultrasound (US) imaging to reveal both functional and structural information in small animals. FDOT is a noninvasive method for examining the fluorophore inside an object from the light distribution of the surface. In FDOT, a 660-nm continuous wave diode laser was used as an excitation source and an electron-multiplying charge-coupled device (EMCCD) was used for fluorescence data acquisition. Both the laser and EMCCD were mounted on a 360-deg rotation gantry for the transmission optical data collection. The structural information is obtained from a 6- to 17-MHz handheld US linear transducer by single-side access and conducts in the reconstruction as soft priors. The rotation ranges from 0 deg to 360 deg; different rotation degrees, object positions, and parameters were determined for comparison. Both phantom and tissue phantom results demonstrate that fluorophore distribution can be recovered accurately and quantitatively using this imaging system. Finally, an animal study confirms that the system can extract a dual-modality image, validating its feasibility for further in vivo experiments. In all experiments, the error and standard deviation decrease as the rotation degree is increased and the error was reduced to 10% when the rotation degree was increased over 135 deg.

Photobiomodulation therapy improves human dental pulp stem cell viability and migration in vitro associated to upregulation of histone acetylation.

This in vitro study evaluated the role of photobiomodulation therapy (PBMT) on viability and migration of human dental pulp stem cells (hDPSCs) and its association to epigenetic mechanisms such as histone acetylation. The hDPSCs were characterized and assigned into control and PBMT groups. For the PBMT, five laser irradiations at 6-h intervals were performed using a continuous-wave InGaAlP diode laser. Viability (MTT), migration (scratch), and histone acetylation H3 (H3K9ac immunofluorescence) were evaluated immediately after the last irradiation. PBMT significantly increased the viability (P = 0.004). Also, PBMT group showed significantly increased migration of cells in the wound compared to the control in 6h (P = 0.002), 12h (P = 0.014) and 18h (P = 0.083) being faster than the control, which only finished the process at 24h. PBMT induced epigenetic modifications in hDPSC due to increased histone acetylation (P = 0.001). PBMT increased viability and migration of hDPSCs, which are related with the upregulation of histone acetylation and could be considered a promising adjuvant therapy for regenerative endodontic treatment.

Effects of pulsed and continuous-wave laser radiation on the fabrication of tissue-engineered composite structures

We studied the formation of a composite from an aqueous dispersed medium with albumin and carbon nanotubes under the action of laser radiation in continuous wave (CW) mode and pulsed mode with a repetition rate of 10 Hz and pulse duration of 16 ns. During the experiments, the temperature was monitored at the site of exposure, as well as its distribution in the liquid. Pulsed solid-state Nd:YAG laser and CW diode laser with an irradiation power of ∼500 mW were used as radiation sources. However, a three-dimensional composite was formed only with constant exposure. The effect of pulsed laser radiation with an intensity corresponding to nonlinear interaction with water dispersion led only to its enlightenment. Thus, it is important not only the energy parameters of radiation but also the frequency of energy portions exposure for the fabrication of tissue-engineered structures (composites). As a result, it was found that the curing of the dispersion and the composite formation occurs under the action of continuous or pulsed (with a high pulse repetition rate) laser radiation at a temperature in the range from 45°C to 50°C; in case the pulse repetition rate is insufficient, composite formation is not observed even under the action of high intensity radiation and heating occurs only to a temperature of ∼40 ° C. This formation process can be generated both in the visible 532 nm and in the infrared 810-nm wavelength ranges. In this case, one of the main conditions is the absence of albumin or cells absorption at these wavelengths so that absorption occurs mainly with single-walled carbon nanotubes. Studies of the surface and internal structure of the composite made it possible to demonstrate the binding of nanotubes to each other. This happened under the influence of laser radiation. This led to high hardness values of the composites. The average value of hardness was 0.26 ± 0.02 GPa.

Micropulse transscleral cyclophotocoagulation: initial results using a reduced energy protocol in refractory glaucoma.

This study evaluates the 6-month safety and efficacy of micropulse transscleral cyclophotocoagulation (MP-TSCPC) in cases of uncontrolled glaucoma/ocular hypertension using a reduced energy protocol. Retrospective analysis of patients undergoing MP-TSCPC from January-April 2018 was carried out. Patients received up to 90s of laser with settings of 2000mW/Cm2 and a duty cycle of 31.3%. A total of 29 patients were included, with a mean age of 64.7 ± 15.1years. The most common diagnosis was primary open angle glaucoma (41.4%) with a mean Logmar visual acuity of 1.5 ± 1.2. All subjects had either undergone intraocular surgery (58.6% filtration surgery) or continuous wave diode laser prior to micropulse treatment. Mean pre-laser IOP was 26.2 ± 11.1mmHg. There was a significant reduction (p < 0.05) in IOP at 1month to 15.8 ± 5.4mmHg (39.7% reduction), at 3months to 15.04 ± 5.25mmHg (42.6% reduction) and at 6months to 18.19 ± 7.47mmHg (30.6% reduction). There was also a corresponding reduction (p < 0.05) in the number of topical agents required to control pressure from a baseline of 3.31 ± 0.97, to 2.72 ± 0.88 at 1month, 2.76 ± 0.91 at 3months and 2.90 ± 1.08 at 6months. Requirements for oral acetazolamide reduced from 41.3% (1/29) at baseline to 3.4% (1/29) at 6months. Success rates were 75.9% at 1month, 79.3% at 3months and 58.6% at 6months. There was no drop in the visual acuity, no change in central retinal thickness and no cases of intraocular inflammation. MP-TSCPC at a decreased duration is effective at reducing intraocular pressure in ethnically diverse glaucoma patients refractory to previous glaucoma laser or surgeries at 6months follow-up, with no significant complications. Further work is needed to confirm efficacy in the long term and to determine optimal settings.

Microwave photonic notch filter based on polarisation multiplexing and cross gain modulation in a semiconductor optical amplifier

A coherent interference-free tunable microwave photonic notch filter with a pair of negative and positive coefficients generated by employing polarisation multiplexing and cross gain modulation in a semiconductor optical amplifier is proposed and demonstrated through simulation results. The negative and positive coefficients of the notch filter are realised through two orthogonal polarisation states of a single continuous wave laser diode. The free spectral range of microwave photonic filter is tuned by varying the differential group delay of a birefringent single-mode fibre. The proposed filter shows good tunability, easy implementation and is cost-effective.