Continuous Wave Diode Laser Research Articles

High-efficiency solar thermophotovoltaic system using a nanostructure-based selective emitter

In this work, we present the design, fabrication, optimization, and experimental results of a high-efficiency planar solar thermophotovoltaic (STPV) system utilizing a micro-textured absorber and a nanostructure multilayer metal-dielectric coated selective emitter fabricated on a tungsten (W) substrate. Light absorptance of more than 90% was achieved at visible and near-infrared wavelengths using the microtextured absorbing surface. The nanostructure selective emitter consists of two thin-film optical coatings of silicon nitride (Si3N4) and a layer of W in between to increase the surface emissivity in spectral regimes matching the quantum efficiency of the thermophotovoltaic (TPV) cells. Gallium antimonide (GaSb)-based TPV cells are used in our STPV design. The experiment was conducted at different operating temperatures using a high-power continuous wave laser diode stack as a simulated source of concentrated incident radiation. Our experimental setup measured a maximum electrical output power density of 1.71 W/cm2 at 1676 K STPV temperature, and the overall power conversion efficiency of 8.4% after normalizing the output power density to the emitter area. This is the highest STPV system efficiency reported so far for any experimental STPV device. The incident optical laser power on the absorber side was 131 W. This is equivalent to a solar concentration factor of ~2100, which is within the practical limit and readily achievable with Fresnel lens setup.

Dual Modality FeS Nanoparticles with Reactive Oxygen Species-Induced and Photothermal Toxicity toward Pathogenic Bacteria.

Bacterial infections pose a major threat to human health, primarily because of the evolution of mutated strains that are resistant to antibiotic treatment. As a viable alternative, several nanoparticles have emerged as attractive antibacterial agents. Herein, we report the development of iron sulfide (FeS) nanoparticles that show dual-modality therapy: namely reactive oxygen species (ROS)-induced toxicity and red-laser induced photothermal therapy. The aqueous synthesized nanoparticles have been characterized based on their size, shape, crystallinity, and magnetic and optical properties. These nanoparticles showed sustained release of Fe2+ ions in an aqueous dispersion. They also have a high absorption cross-section in the visible and near infra-red regions and could be excited by a continuous wave diode laser of wavelength 635 nm leading to significant hyperthermia. Nanoparticle treatment, followed by light irradiation, led to significant cell death in two ghastly pathogenic bacterial strains. Stepwise enhancement of intrabacterial ROS levels, as a result of nanoparticle treatment followed by light activation, has been identified as the primary antibacterial mechanism.

Optical Coherence Tomography/Angiography-Guided Tumor Ablation With a Continuous-Wave Laser Diode

Laser ablation can be an effective modality for treatment, but it is complicated to apply continuous-wave (CW) light sources for laser ablation because of the unpredictable photothermal damage. In this study, an integrated theranostic system combining a low-cost CW laser diode with optical coherence tomography (OCT)/angiography (OCTA) was utilized for the in vivo ablation of tumor tissues. To examine the effect of laser exposure on tissue scattering characteristics, the OCT backscattering intensities of non-ablated and ablated tissues were analyzed, and the effect on the skin microvasculature produced by laser ablation was quantitatively evaluated. Moreover, the integrated system and the proposed method were implemented for the treatment of skin tumor on the mouse model. The obtained results indicate that the developed laser ablation system can effectively remove tumor tissues with controllable photodamage under OCT/OCTA guidance and that the system cost may be significantly reduced by using the CW laser diode.

Effectiveness and Safety of Long Duration versus Short Duration Diode Laser Transscleral Cyclophotocoagulation.

PurposeTo compare the efficacy and safety of diode laser transscleral cyclophotocoagulation using either the long duration or short duration protocol.MethodsRetrospective series of 23 consecutive patients with glaucoma who underwent continuous-wave diode laser transscleral cyclophotocoagulation from August 2016 to July 2018 at a tertiary hospital in Hong Kong. Laser pulse duration for the long and short duration protocols was defined as 3.0–4.0 and 1.5–2.0 s, respectively.ResultsThere were 15 male and 8 female Chinese subjects (23 eyes), age 49–90 (71.3 ± 2.7), with 10 subjects that underwent long duration cyclophotocoagulation (power 1239.2 ± 78.3 mW, spots 13.9 ± 1.4) and 13 subjects that had short duration cyclophotocoagulation (mean power 1817.3 ± 85.7 mW, spots 14.4 ± 1.0). Six months after long and short duration cyclophotocoagulation, intraocular pressure decreased significantly from 29.9 ± 7.8 to 21.1 ± 6.5 (p < 0.01), and from 35.4 ± 2.7 to 24.1 ± 3.4 (p = 0.04), respectively, while glaucoma medications decreased significantly by 1.4 ± 0.5 (p = 0.02) in the long duration group only. Reduction of medications after short duration cyclophotocoagulation was less and did not reach statistical significance (0.9 ± 0.9, p = 0.15). There was no significant difference of visual deterioration and complication rates.ConclusionBoth types of cyclophotocoagulation were equally effective in lowering intraocular pressure by 6 months, but the short duration protocol, using higher laser power, was able to achieve a greater and earlier reduction, at 3 months. However, the long duration protocol, using less laser power, appears better at reducing medication requirement by 6 months.

Colloidal (Gd0.98Nd0.02)2O3 nanothermometers operating in a cell culture medium within the first and second biological windows

Non-contact, self-referenced and near-infrared luminescent nanothermometers have been recognized as emerging tools in the fields of nanomedicine and nanotechnology due to their great capability of precise temperature readout at the nanoscale and real-time deep-tissue imaging. However, the development of multifunctional and biocompatible luminescent nanothermometers operating within the optically transparent biological windows with high thermal sensitivity (>2.0%/K) remains challenging. Here, we present (Gd0.98Nd0.02)2O3 nanothermometers operated effectively within the first and second biological windows upon continuous-wave laser diode excitation at 808 nm. Ratiometric thermometric parameters are defined by the relative changes in the emission intensities originating from the two Stark components of the 4F3/2 level (R2 and R1) to the 4I9/2 (900–1000 nm), 4I11/2 (1035–1155 nm) and 4I13/2 (1300–1450 nm) multiplets. The thermometric parameters are evaluated for colloidal samples in a cell culture medium and powder samples, and the highest thermal sensitivity (2.18%/K at 298 K) is attained for the former in the first biological window (both the excitation and emission in the 800–965 nm range). The repeatability and temperature uncertainty are 99% and 1.2 K, respectively. The nanothermometers are biocompatible with human MNT-1 melanoma and HaCaT cells for 24 h of exposure and nanoparticle concentration up to 0.400 mg/mL, showing their potential for applications in nanomedicine, e.g., intracellular imaging and temperature mapping.

Highly efficient tunable picosecond deep ultraviolet laser system for Raman spectroscopy.

We present a narrowband laser system tunable from 219 to 236 nm for deep ultraviolet (DUV) Raman spectroscopy. The demonstrated laser system produces 6.7 ps nearly transform-limited pulses with energy up to 0.36 µJ at 100 kHz repetition rate. The system consists of a two-stage optical parametric amplifier (OPA) of a narrowband continuous wave diode laser and subsequent frequency conversion to the DUV radiation. We achieve more than 300 mW in the signal wave using ${{\rm LiB}_3}{{\rm O}_5}$LiB3O5 (LBO) and ${{\rm BaB}_2}{{\rm O}_4}$BaB2O4 (BBO) crystals, with the total 2.7 W pump after the two-stage OPA. We reach 12% conversion efficiency of the OPA signal wave into the DUV radiation using type-I phase matching in the BBO crystal. Finally, we demonstrate the applicability of the system for DUV Raman spectroscopy by collecting a high dynamic range, high spectral resolution spontaneous Raman spectrum of air.

QAM Transmission over RoF Using Fabry Perot Laser Diode and Continuous Wave Laser Diode

This paper introduces the Quadrature Amplitude Modulation (QAM) Radio over Fiber (RoF) framework dependent on Optical Frequency Comb (OFC) generation utilizing Fabry-Perot Laser Diode (FPLD) and Continuous Wave Laser Diode (CWLD). In this, optical Millimeter-Wave (MMW) can be created ether utilizing ease FPLD with an outside optical infusion or a continuous wave laser diode. At the base, optical MMW can be recognized by utilizing photodetector in the two transmissions. The experimental results are explained by using the constellation and eye diagram.

Delivery Strategies for Skin: Comparison of Nanoliter Jets, Needles and Topical Solutions

Drug diffusion within the skin with a needle-free micro-jet injection (NFI) device was compared with two well-established delivery methods: topical application and solid needle injection. A permanent make-up (PMU) machine, normally used for dermal pigmentation, was utilized as a solid needle injection method. For NFIs a continuous wave (CW) laser diode was used to create a bubble inside a microfluidic device containing a light absorbing solution. Each method delivered two different solutions into ex vivo porcine skin. The first solution consisted of a red dye (direct red 81) and rhodamine B in water. The second solution was direct red 81 and rhodamine B in water and glycerol. We measured the diffusion depth, width and surface area of the solutions in all the injected skin samples. The NFI has a higher vertical dispersion velocity of 3 × 105μm/s compared to topical (0.1 μm/s) and needle injection (53 μm/s). The limitations and advantages of each method are discussed, and we conclude that the micro-jet injector represents a fast and minimally invasive injection method, while the solid needle injector causes notable tissue damage. In contrast, the topical method had the slowest diffusion rate but causes no visible damage to the skin.

946 nm 25 mJ/3 ns Nd:YAG laser based on regenerative amplification of pulses

Regenerative amplification of 946 nm pulses which are sliced from 12 mW continuous wave laser diode is reported. Near-transform-limited 2.9 ns pulses with highly stable and smooth temporal shape were obtained with the energy of 25 mJ/50 Hz and M 2 < 1.2.

Continuous-wave laser diodes based on epitaxially integrated InGaAs/AlGaAs/GaAs heterostructures

We report the results of the development and investigation of the main characteristics of integrated laser emitters for the spectral range from 1040 to 1080 nm. These devices are fabricated using epitaxially integrated InGaAs/AlGaAs/GaAs heterostructures with one or two emitting regions, and measurements are performed in pulsed, quasi-continuous, and continuous-wave pump regimes. It is found that along with the obvious advantage of integrated emitters − an increase in the output optical power, they also have a significant limitation, which consists in increasing the amount of released heat. Despite this, it is shown that such integrated double laser diodes operate efficiently in the continuous-wave generation regime (P max ∼ 6 W), demonstrating a 1.7-fold increase in the differential quantum efficiency as compared to single laser diodes.

Third-order nonlinear optical properties of three chlorinated thienyl chalcones derivatives: synthesis, structural determination and Hirshfeld surface analysis

AbstractThree chlorinated theinyl chalcone derivatives, namely (E)-1-(5-chlorothiophen-2-yl)-3-(4-(methylthio)phenyl)prop-2-en-1-one (I), (E)-1-(5-chlorothiophen-2-yl)-3-(4-(dimethylamino)phenyl)prop-2-en-1-one (II) and (E)-1-(5-chlorothiophen-2-yl)-3-(2,3-dihydrobenzofuran-5-yl)prop-2-en-1-one (III), were synthesized and their crystal structures were determined by single-crystal X-ray diffraction analysis. CompoundsI,IIandIIIcrystallize in the monoclinic space groupsP 21/c(centrosymmetric),P 21/n(centrosymmetric) andPc(non-centrosymmetric), respectively. In all three compounds, the molecules are in a relatively planar conformation and adopt atransconfiguration with respect to the C=C double bond. The crystal packings are stabilized by weak hydrogen-bonds, π · · · π, C–H · · · π and C–Cl · · · π interactions. The intermolecular contacts and lattice energies were further analyzed by Hirshfeld surface analysis. The third-order nonlinear optical properties of these chalcone derivatives were investigated using the single beam Z-scan technique with a 5 mW continuous wave diode laser operating at 635 nm, where compoundIshowed the highest potential for optical application with its exclusive nonlinear refractive index and nonlinear susceptibility.

An experimental investigation of the effects of diode laser surface hardening of AISI 410 stainless steel and comparison with furnace hardening heat treatment

This study investigated the ability of the continuous wave diode laser surface hardening of AISI 410 martensitic stainless steel with a maximum power of 1600 W. Variable process parameters scanning speed (4–7 mm/s), laser power (1200–1600 W) and stand-off distance (65–75 mm) were considered in this study. Microhardness, the geometry of hardened layer (depth and width), microhardness deviation from the base metal microhardness (MHD), microstructure analysis of the laser-hardened zone through optical microscopy and field emission scanning electron microscopy and percentage of the ferrite phase in AISI 410 microstructure by using Clemex software were considered as process output responses. Results confirmed that by increasing the laser power and reducing the scanning speed, the surface hardness and the depth of hardness increase. It is also revealed the width of the hardened area increases by enhancing stand-off distance and reducing the laser power. Maximum hardness of 630 HV0.3 with 2.2 mm depth is obtained. Also, the furnace hardening heat treatment is compared with the laser hardening process. Microstructure, microhardness, and impact tests of the two processes are compared. Results showed that the hardness of the diode laser is 1.4 times the hardness of the furnace hardening heat treatment.

Toward Wearable Healthcare: A Miniaturized 3D Imager With Coherent Frequency-Domain Photoacoustics.

Medical monitoring is undergoing a translation from the hospital-based system to the personalized home-based system. With the aim of wearable application of photoacoustic technique, we propose a miniaturized photoacoustic 3D imager for superficial medical imaging. By employing the compact continuous-wave laser diode based optical irradiation and an ultrathin 2D matrix array based photoacoustic detection in the coherent frequency domain, a wearable imaging probe with a size of about 80 × 25 × 24mm3 and a weight of 21 g is developed. At the backend, an FPGA controlled Howland current source drives the laser diodes to excite linear frequency modulated optical irradiation. Recorded by a portable multichannel data acquisition system, the generated photoacoustic responses are firstly compressed with the coherent frequency domain photoacoustic method and then extrapolated in the wavenumber-frequency domain for fast image reconstruction. With three-wavelength (450nm, 638nm, and 808nm) laser irradiation, photoacoustic imaging can be operated multispectrally, endowing the developed imager with functional imaging capability in 3D space. With the imager worn on the human forearm, hemoglobin oxygen saturation level in superficial arm vasculature can be long-term monitored with high stability. When the imager is applied for imaging in a relatively large area (e.g., early melanoma detection in the human breast), flexible scanning in a handheld manner can be performed. This work opens the application potential of photoacoustic technique in a broad range of areas, including personalized healthcare, home health monitoring, and long-term physiologic monitoring.

Interference-free Detection of Lipid-laden Atherosclerotic Plaques by 3D Co-registration of Frequency-Domain Differential Photoacoustic and Ultrasound Radar Imaging

As lipid composition of atherosclerotic plaques is considered to be one of the primary indicators for plaque vulnerability, a diagnostic modality that can sensitively evaluate their necrotic core is highly desirable in atherosclerosis imaging. In this regard, intravascular photoacoustic (IVPA) imaging is an emerging plaque detection modality that provides lipid-specific chemical information of arterial walls. Within the near-infrared window, a 1210-nm optical source is usually chosen for IVPA applications because lipid exhibits a strong absorption peak at that wavelength. However, other arterial tissues also show some degree of absorption near 1210 nm and generate undesirable interfering PA signals. In this study, a novel wavelength-modulated Intravascular Differential Photoacoustic Radar (IV-DPAR) modality was introduced as an interference-free detection technique for a more accurate and reliable diagnosis of plaque progression. By using two low-power continuous-wave laser diodes in a differential manner, IV-DPAR could efficiently suppress undesirable absorptions and system noise, while dramatically improving system sensitivity and specificity to cholesterol, the primary ingredient of plaque necrotic core. When co-registered with intravascular ultrasound imaging, IV-DPAR could sensitively locate and characterize the lipid contents of plaques in human atherosclerotic arteries, regardless of their size and depth.

A Sensitive Carbon Monoxide Sensor Based on Photoacoustic Spectroscopy with a 2.3 μm Mid-Infrared High-Power Laser and Enhanced Gas Absorption.

A photoacoustic spectroscopy (PAS)-based carbon monoxide (CO) gas sensor with a high-power laser and an enhanced gas absorption was demonstrated. The light source was a distributed feedback (DFB), continuous wave (CW) diode laser with a high output power of ~8 mW to give a strong excitation. The target gas received optical absorption enhanced two times by using a right-angle prism reflecting the laser beam. In order to reduce the noise from the background, wavelength modulation spectroscopy (WMS) and second-harmonic detection techniques were used. The modulation frequency and modulation depth were optimized theoretically and experimentally. Water vapor was added in the PAS sensor system to increase the vibrational–translational (V–T) relaxation rate of the CO molecule, which resulted in an ~8 times signal enhancement compared with the using of a dry CO/N2 gas mixture. The amplitude of the 2f signal had a 1.52-fold improvement compared to the one with only one time absorption. The experimental results showed that such a sensor had an excellent linear response to the optical power and gas concentration. At 1 s integration time, a minimum detection limit (MDL) for CO detection of 9.8 ppm was achieved. The long-term stability of the sensor system was evaluated with an Allan deviation analysis. When the integration time was 1100 s, the MDL improved to be 530 ppb. The detection performance of such a PAS-based CO sensor can be further improved when a laser with a higher output power and increasing optical absorption times is used.

Numerical study of the effect of diode laser-induced optical, thermal, and residual stresses on CZTS thin-films

This paper presents a numerical study of the continuous wave (CW) diode laser processing of Cu2ZnSnS4 (CZTS) thin-film. The CZTS film’s structural, optical, surface morphological, and electrical properties improvement due to the localized and instantaneous heating provided by the diode laser mandates a detailed understanding of how laser processing affects the CZTS thin-film during thermal treatment to ensure a high-quality processing result as well as optimization and characterization. However, understanding of such process suffers from the restricted accessibility as most of the important phenomena occur inside the film during a very short duration time, where numerical simulations can serve as a valuable alternative to gain accessibility. This contribution, therefore, presents a numerical approach to examine the CW diode laser-induced thermal effect on the CZTS thin-film. A numerical model in OpenFOAM has been developed to elucidate the influence of laser processing parameters on the optical, heat transfer, and residual stress, as well as design architecture, of the CZTS thin-films. The model results predicted that the inappropriate settings of the laser parameters, as well as the thickness of the CZTS films, generate thermal gradient within the film and hence induce delamination and propagation of crack at the interfaces. The developed model helped in understanding the laser-induced thermal behavior of the CTZS thin-film and can be utilized as a guide to using lasers as an effective tool for fabricating the high-efficiency CZTS thin-film based solar cells.

Novel High-Power, High Repetition Rate Laser Diode Pump Modules Suitable for High-Energy Class Laser Facilities

The latest generation of high-energy-class pulsed laser facilities, under construction or planned, such as EuPRAXIA, require reliable pump sources with high power (many kW), brightness (&gt;1 MW/cm2/sr) and electro-optical conversion efficiency (&gt;50%). These new facilities will be operated at high repetition rates (around 100 Hz) and only diode lasers are capable of delivering the necessary performance. Commercial (quasi-continuous wave, QCW) diode laser pulse-pump sources are, however, constructed as low-cost passively cooled stacked arrays that are limited either in brightness, efficiency or repetition rate. Commercial continuous wave diode laser pumps constructed using microchannel coolers (as used in high-value industrial machine tools) can fulfil all requirements, but are typically not preferred, due to their cost and complexity and the challenges of preventing cooler degradation. A custom solution is shown here to fill this gap, using advanced diode lasers in a novel passive side-cooling geometry to realize 100 … 200 Hz pump modules (10%–20% duty cycle) that emit peak power of 6 kW at wavelength = 940 nm. The latest performance of these modules is summarized and compared to literature. We show that a brightness &gt;1 MW/cm2/sr can be efficiently delivered across a wide range of laser pulse conditions with 10% duty cycle (pulse width: 100 µs … 100 ms … cw, repetition rate up to 1 kHz). Furthermore, we describe how these pumps have been used to construct and reliably operate (&gt;109 pulses without degradation) in high-energy-class regenerative and ring amplifiers at the Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (MBI). We also show first results on 100 Hz pumping of cryogenically cooled solid-state Yb:YAG slab amplifiers, as anticipated for use in the EuPRAXIA laser, and note that peak temperature is disproportionately increased, indicating that improved cooling and more detailed studies are needed.

Wavelength, repetition rate, and pulse width tunable high average power narrow linewidth 1.5 μm fiber amplifier

Abstract Here, a wavelength, repetition rate, and pulse width tunable high average power narrow linewidth 1.5 μm all-fiber amplifier has been achieved by directly modulating a continuous-wave single-frequency diode laser using an acousto-optic modulator. The laser wavelength can be precisely tuned from 1530 nm to 1570 nm. The repetition rate and pulse width are also conveniently tunable. The maximum output average power is more than 2.5 W and the laser linewidth is at the range of 150–500 MHz. It has wide applications in tunable mid-infrared hollow-core fiber gas lasers, mid-infrared laser generation by nonlinear frequency conversion, fiber radar, coherent combination, and so on.

Laser ablation synthesis of silver nanoparticles in water and dependence on laser nature

Silver nanoparticles have been synthesized by a one step, easy, fast and green method. The nanoparticles were prepared in de-ionized water by laser ablation method using two lasers, a continuous wave (CW) diode laser and a pulsed Nd:YAG laser. The purpose of the experiment is to compare the role of nature of the laser for production of better NPs. The prepared silver nanoparticles were characterized for their, structural, physical and optical properties. The structural properties of the synthesized nanoparticles were characterized by X-ray Diffraction and the nanoparticles were found to be crystalline. The physical properties were analyzed by Atomic Force Microscopy which confirmed spherical and nanometer sized nanoparticles. The average size was 20 nm and 9 nm for continuous and pulsed laser respectively. The optical properties were analyzed by UV–Visible spectroscopy where band gap energy was investigated and increase in band gap energy as compared to bulk was observed. The green nature of laser ablation method, surface chemistry and chemical contamination of the surface of prepared nanoparticles were analyzed by Fourier Transform Infrared Spectroscopy. The thermal conductivity of the nanoparticles colloidal solutions (nanofluids) was calculated and an enhancement of 16% and 27% was observed for CW and pulsed laser prepared nanofluids respectively as compared to base liquid (de-ionized water).

Multiple luminescence spanning the UV to NIR regions of Tm3+-doped silica glass microspheres pumped by 1527 nm

Fluorescence spectra of Tm3+-doped silica glass microspheres under excitation of a continuous wave diode laser at 1527 nm were investigated. It showed rich upconversion emissions from the high-energy states of Tm3+ ions, which spanned from the ultraviolet (UV) to near-infrared (NIR). Analysis indicated that the purple light emission came from a six-photon upconversion process. What's more, a broadband fluorescence emission was observed in a wavelength range of 620–935 nm. The high power density was a main advantage by confining the light in the microsphere cavities. The multiple fluorescence upconversion emissions of Tm3+-doped silica glasses under ∼1550 nm excitation may open a new door to explore the future visible light communication technology.