Continuous Wave Semiconductor Laser Research Articles

Enhanced UV photodetector using Mg-doped ZnO sub-micro tube films synthesized through laser-assisted chemical bath growth

This study presents the fabrication of MgxZn(100-X)O thin films (TFs) with Mg concentration levels (x) of 0.5 at%, 1.0 at%, 1.5 at%, and 2.0 at% on glass substrates using the novel laser-assisted chemical bath growth (LACBG) method, aimed at investigating their photo-response for potential UV photodetector applications. Utilizing a continuous wave semiconductor laser with a 444.5 nm wavelength, 1 W power, and 6 min of irradiation, the LACBG method successfully produced high-quality Mg-doped ZnO TFs. These films were deposited on glass substrates coated with silver (Ag) to serve as electrode contacts for constructing a metal-semiconductor-metal (MSM) UV photodetector. The structural, optical, and electrical properties of the TFs were thoroughly analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to examine the crystal microstructures and surface morphologies, revealing vertically aligned hexagonal symmetrical sub-micro tubes. In contrast, energy dispersive X-ray (EDX) analysis confirmed successful Mg incorporation into the ZnO lattice. UV–visible absorbance spectra indicated a blue shift in the absorption edge and increased band gap energy from 3.24 eV to 3.67 eV with rising Mg content. The UV photodetectors, particularly those with 2.0 at% Mg-doped ZnO TFs, demonstrated significantly enhanced UV responsiveness attributed to optical confinement, high surface-to-volume ratio, and superior structural quality. Performance metrics for the 2.0 at% Mg-doped ZnO TFs included a responsivity of 10.60 A/W, external quantum efficiency of 34.10, specific detectivity of 2.25 × 107 Jones, noise equivalent power of 5.34 × 10−11 W, rise time of 86.9 ms, and decay time of 324.4 ms. These findings underscore the potential of Mg-doped ZnO TFs for high-performance UV photodetection applications. The novelty of this study lies in utilizing LACBG to achieve high-quality Mg-doped ZnO TFs, offering a cost-effective, low-temperature method that enhances UV photodetector performance.

Investigating the role of Ag-doped ZnO thin films in UV photodetectors produced via laser assisted chemical bath growth technique

This study introduces the innovative fabrication of Ag-doped ZnO thin films (AgxZnO(100−x) TFs) with varying silver (Ag) concentrations (x) of 0.5, 1.0, 1.5, and 2.0 at% on glass substrates using a simple and cost-effective method known as laser-assisted chemical bath growth (LACBG). This process aims to create metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors. A continuous wave semiconductor laser with a 444.5 nm wavelength, 5 W power, and 6 min irradiation time was employed to synthesize high-quality Ag-doped ZnO TFs on the glass substrate. Ag electrodes were utilized as Schottky contacts to form MSM UV photodetectors. Structural and morphological analyses conducted using XRD and SEM revealed vertically aligned nanorods and nanoflowers with a high c-axis orientation and hexagonal wurtzite facets, while EDX confirmed Ag incorporation into the ZnO lattice. The UV–Visible absorbance spectra indicated a decrease in bandgap from 3.28 to 2.84 eV with increased Ag content. The current-voltage (I–V) characteristics of the Ag-doped ZnO TFs UV photodetector showed significantly enhanced conductivity at a 2.0 at% concentration level, achieving a responsivity of 10.78 A/W, an external quantum efficiency of 34.67 % at −3 V bias voltage. Finally, the modified device exhibited a sensitivity of 14661.9 %, a gain of 147.62, and a detectivity of 2.25 ×107 Jones, demonstrating its suitability for optoelectronic applications.

Detection of lead ions in aqueous solutions using laser-induced fluorescence from their chelates with YZS60 resins

Lead ions in aqueous solutions were detected by laser-induced fluorescence spectroscopy (LIFS) after the ions were removed from the solutions by YZS60 resin-based chelating reaction, and excited by a continuous wave semiconductor laser at 447 nm. Significant enhancement of fluorescence emission was observed, resulting in improving the detecting sensitivity of heavy metal ions in aqueous solutions. The limit of detection was 0.0011 mg/L, which was lower than the permissible level of drinking water 0.01 mg/L. The results indicate that the laser-induced fluorescence spectroscopy combined with the ion removing technique could be applied for effectively detecting lead ions in aqueous solutions, and this method has the characteristics of low device cost, simple operation and nondestructive testing of samples.

Synthesis ZnO nanoclusters micro active area using continues wave blue laser-assisted chemical bath deposition based on UV photodetector

In this study, zinc oxide (ZnO) thin films were utilized to create metal–semiconductor–metal (MSM) structured ultraviolet (UV) photodetectors using laser assisted chemical bath deposition (LACBD). For the first time, LACBD has successfully manufactured zinc oxide (ZnO) nanoclusters (NCs) with high-quality structural, optical, and electrical properties on a glass substrate coated with iron (Fe) to construct an MSM UV photodetector with high responsivity. The thin film was created by irradiating the chemical bath in situ using a continuous wave semiconductor laser with wavelength(460 nm), output power (1 W), and irradiation laser time (30 min). The thin film was characterized using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) analyses, and X-ray diffractometry (XRD). Our findings revealed that LACBD promoted the development of a high-crystallinity ZnO thin film. The effectiveness of ZnO NCs in UV detection has also been examined to account for the potential of these nanostructures. The device's current-voltage (I-V) characteristics were tested in dark and light situations, confirming the UV photodetector's excellent responsiveness and stability. Optical confinement, a high surface-to-volume ratio, and the superior structural quality of the NCs, as confirmed by time-resolved spectroscopy, are all factors in the great photodetector performance.

Micro spot ZnO nanotubes using laser assisted chemical bath deposition: A low-cost approach to UV photodetector fabrication

Due to its outstanding characteristics across a wide variety of applications, such as electrical, photonic, electrochemical, and electromechanical devices, one-dimensional Zinc oxide (ZnO) is one of the most promising nanostructures. Using a continuous wave semiconductor laser with a wavelength of 460 nm and a power of 1 W, functional ZnO nanostructures known as nanotubes (NTs) with high-quality structural, optical, and electrical properties on a glass substrate coated with iron (Fe) to construct a UV photoconductive detector with high responsivity were produced for first time by using a simple and quick laser assisted chemical bath deposition (LACBD). X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray (EDX)analyses were used to investigate the evolution of the material's physical and structural characteristics. Our findings revealed that laser-assisted in-situ irradiation of the chemical solution resulted in faster growth of ZnO thin films. To account for the potential of these nanostructures, the effectiveness of ZnO nanotubes (NTs) in ultraviolet (UV) detection has also been investigated. The NT-based photodetector has outstanding stability and responsiveness in both dark and light conditions. Exciton confinement is identified using time-resolved spectroscopy, suggesting that the high surface-to-volume ratio, optical confinement, and high structural quality of the NTs are responsible.

Classification of IQ-Modulated Signals Based on Reservoir Computing With Narrowband Optoelectronic Oscillators

We numerically perform the classification of IQ-modulated radiofrequency signals using reservoir computing based on narrowband optoelectronic oscillators (OEOs) driven by a continuous-wave semiconductor laser. In general, the OEOs used for reservoir computing are wideband and are processing analog signals in the baseband. However, their hardware architecture is inherently inadequate to directly process radiotelecom or radar signals, which are modulated carriers. On the other hand, the high- Q OEOs that have been developed for ultra-low phase noise microwave generation have the adequate hardware architecture to process such multi-GHz modulated signals, but they have never been investigated as possible reservoir computing platforms. In this article, we show that these high- Q OEOs are indeed suitable for reservoir computing with modulated carriers. Our dataset (DeepSig RadioML) is composed with 11 analog and digital formats of IQ-modulated radio signals (BPSK, QAM64, WBFM, etc.), and the task of the high- Q OEO reservoir computer is to recognize and classify them. Our numerical simulations show that with a simpler architecture, a smaller training set, fewer nodes and fewer layers than their neural network counterparts, high- Q OEO-based reservoir computers perform this classification task with an accuracy better than the state-of-the-art, for a wide range of parameters. We also investigate in detail the effects of reducing the size of the training sets on the classification performance.

Semiconductor laser cladding of an Fe-based alloy on nodular cast iron

Coatings on the surface of nodular cast iron were prepared using a continuous wave semiconductor laser as a function of laser power. The cross-sections were etched by aqua regia to reveal the microstructure, and then the surfaces were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The phase composition was analyzed by X-ray diffraction (XRD), and the hardness was measured using a Vickers hardness tester. The wear behaviors were examined using a microscopic wear test machine. The results revealed that the microstructure of the coatings was mainly composed of martensite and austenite. As the laser power increased, a wider columnar dendrite zone and an equiaxed dendrite zone can be observed, and the proportion of martensite decreased and retained austenite increased. The hardness first increased and then decreased with the increasing laser power. Solidification cracking was detected at higher laser power. All the worn surfaces at different laser powers exhibited typical adhesive wear, and the coatings with more martensite had better wear resistance.

Synthesis, growth, crystal structure, thermal, linear and nonlinear opticalanalysis of new extended π-conjugated organic material based on methyl pyridinium compound of 4-(4-(4-(dimethylamino) phenyl)buta-1,3-dienyl)-1-methylpyridinium p-styrenesulfonate hydrate

In this research work, a new extended π-conjugated chromophore of 4-[4-(4-dimethylamino-phenyl) buta-1,3-dienyl]-1-methyl pyridinium p-styrenesulfonate (DCSSS) is synthesized. The present work demonstrates that 4-[4-(4-dimethylamino-phenyl) buta-1,3-dienyl]-1-methyl pyridiniump-styrene sulfonate hydrate (DCSSS·H2O) crystallizes with centrosymmetric space group (P1¯). The asymmetric structure comprises of 4-((1E,3E)-4-(4-(dimethylamino)phenyl)buta-1,3-dien-1-yl)-1-methylpyridinium cation (C18H21N2+), 4-vinylbenzenesulfonate (C8H7O3S−) anion and a water molecule. The crystal structure is stabilized by C–H⋯O, O–H⋯O, O–H⋯S types of H-bonding interactions along with π–π stacking interaction and C–H···π interactions. In DCSSS, the anion, cation and water molecule are connected by four Owater–H···Owater and Ccation–H···Osulfonate hydrogen bonds, generating R66 (18) graph-set notation. This ring motif is sandwiched between two another R44 (12) ring motif, which are generated by four O–H⋯O bonds between anion, cation and water molecules, forming laddar lying parallel to the ab plane. The material was characterized by single crystal XRD method, CHN, NMR, FTIR, FT-Raman, TG-DSC and UV-Vis and luminescence studies. To the best of author's knowledge, all these characterizations were made for the first time. We have also emphasized the role of hydrogen bonding on molecular packing to obtain perfectly aligned cations. Third harmonic generation efficiency of the compound is measured by Z-scan technique with continuous wave semiconductor laser of wavelength 532 nm to realize the nonlinear optical properties DCSSS molecule.

Distributed Temperature Sensing Using Cyclic Pseudorandom Sequences

An alternative for commercial Raman-Optical Time Domain Reflectometry (OTDR) distributed temperature sensors is presented, where a pseudorandom pulse sequence is used to increase the signal to noise ratio. Additionally, a deconvolution algorithm is proposed to eliminate distortions in the reconstruction arising from the real correlation properties of the sensing signal. An improvement in SNR of a factor 11 respect to the Raman-OTDR method at the same peak power was achieved, allowing 2 m and 1.5 °C resolution in a 6 s measurement using a 90-mW Continuous wave semiconductor laser.

Continuous-wave mid-infrared photonic crystal light emitters at room temperature

Mid-infrared photonic crystal enhanced lead-salt light emitters operating under continuous-wave mode at room temperature were investigated in this work. For the device, an active region consisting of 9 pairs of PbSe/Pb0.96Sr0.04Se quantum wells was grown by molecular beam epitaxy method on top of a Si(111) substrate which was initially dry-etched with a two-dimensional photonic crystal structure in a pattern of hexagonal holes. Because of the photonic crystal structure, an optical band gap between 3.49 and 3.58 µm was formed, which matched with the light emission spectrum of the quantum wells at room temperature. As a result, under optical pumping, using a near-infrared continuous-wave semiconductor laser, the device exhibited strong photonic crystal band-edge mode emissions and delivered over 26.5 times higher emission efficiency compared to the one without photonic crystal structure. The output power obtained was up to 7.68 mW (the corresponding power density was ~363 mW/cm2), and a maximum quantum efficiency reached to 1.2%. Such photonic crystal emitters can be used as promising light sources for novel miniaturized gas-sensing systems.

Dual optical frequency comb architecture with capabilities from visible to mid-infrared.

In this paper, a new approach to dual comb generation based on well-known optical techniques (Gain-Switching and Optical Injection Locking) is presented. The architecture can be implemented using virtually every kind of continuous-wave semiconductor laser source (DFB, VCSEL, QCL) and without the necessity of electro-optic modulators. This way, a frequency-agile and adaptive dual-comb architecture is provided with potential implementation capabilities from mid-infrared to near ultraviolet. With a RF comb comprising around 70 teeth, the system is validated in the 1.5 μm region measuring the absorption feature of H13CN at 1538.523 nm with a minimum integration time of 10 μs.

Compact 405-nm random-modulation continuous wave lidar for standoff biological warfare detection

A compact bioaerosol standoff system was developed and tested for bio warfare agent stimulant aerosol detection. It used a continuous-wave semiconductor laser diode with an output power of 100 mW and a wavelength of 405 nm. It was modulated with a pseudorandom code at 100 MHz to provide the 1.5 m range resolution for both scattering and fluorescence detection. A 200-mm-diameter Cassegrain telescope and four photon-counting detection channels centered at 405 nm (two polarization detection channels), 450 nm, and 530 nm constituted the optical receiver. A field-programmable gate array chip was controlled to generate the laser driver signal and record four synchronized channel signals. Field tests were performed with stimulant aerosols of Bacillus subtilis, Staphylococcus aureus, and yeast. The detected biological warfare stimulant aerosol lidar was released at ranges of several hundred meters. The preliminary result showed that the fluorescence channel detected the stimulants at ranges up to 90 m and the elastic scattering channel up to 200 m.

Technique for measuring laser radiation intensity in biological tissues

AbstractLaser methods, such as laser-induced fluorescence diagnostics, photodynamic therapy (PDT), and hyperthermia, are finding increasing use in medicine. Irradiation can be performed both with and without contact on the tissue surface. In the case of contact irradiation, especially when laser radiation is introduced into biological tissue through an optical fiber, it is important to know the processes taking place at the irradiation fiber end. These processes affect diffusely reflected radiation which returns to the fiber. By analyzing backscattered radiation, we can evaluate the quality of the radiation procedure and the state of the fiber end. The objectives of this study were to develop a method and device for measuring backscattered radiation power and using this method, to determine the time and temperature ranges realized in PDT and hyperthermia.Light propagation is discussed in bent optical fibers. A technique is proposed for measuring laser radiation intensity in the optical fiber bend. Based on this technique, a system was developed for monitoring the laser radiation dose absorbed in biological tissues. We studied samples of bovine liver, muscle and brain tissues. Experiments were performed using a 675 nm, 100–2200 mW continuous wave semi-conductor laser. Laser radiation was delivered through a silica/polymer optical fiber. Data concerning the temperature and transmitted radiation intensity was acquired.Modeling of the light propagation in a bent optical fiber showed that the sensitivity of the method depends on the position of the photodetectors, but is independent of the loop number of the optical fiber. The results of experiments are presented using different types of biological tissues. We obtained the experimental dependencies of backward and transmitted radiation intensities and the temperature of the tissue surface in the irradiated region on the irradiation time measured with a flat-end fiber. The characteristic ranges of tissue heating caused by irradiation were determined for use in clinical practice.The optical parameters of biological tissues change with increasing temperature. This affects the intensity of transmitting radiation and diffuse radiation entering the fiber. The change in the backscattered radiation intensity greatly depend on the temperature of the irradiated area. The control of the irradiation of biological objects provides an efficient delivery of laser radiation to biological tissues and increases hyperthermia and PDT treatment effect.

Two-channel opto-electronic chaotic communication system

We propose and implement experimentally an opto-electronic chaotic communication system based on chaos synchronization, which uses two channels: the electronic channel for synchronization and the optical channel for information transmission. Both the transmitter and the receiver contain identical chaotic Rössler-like electronic circuits and identical continuous wave semiconductor lasers. The circuit in the receiver is synchronized with the circuit in the transmitter by one of the variables via the electronic channel, while another variable serves to drive the laser pump current chaotically. Due to the functional dependence of the circuit variables, the signals transmitted through the electronic and optical channels are also functionally dependent. A message is encrypted into the laser output in the transmitter and sent to the receiver via the optical channel, where the received waveform is compared with the laser output in the receiver. Since the lasers in the transmitter and in the receiver are completely synchronized, the message is retrieved with a very good precision.

Antiinflammatory effect of low-level laser therapy on Staphylococcus epidermidis endophthalmitis in rabbits

A rabbit model of endophthalmitis was established to evaluate the antiinflammatory effect of low-level laser therapy (LLLT) as an adjunct to treatment for Staphylococcus epidermidis endophthalmitis. Rabbits were randomly divided into three groups to receive intravitreal injections into their left eye: group A received 0.5mg vancomycin (100μl), group B received 0.5mg vancomycin + 0.2mg dexamethasone (100μl), and group C received 0.5mg vancomycin (100μl) and continuous wave semiconductor laser irradiation (10mW, λ = 632nm) focused on the pupil. Slit lamp examination and B-mode ultrasonography were conducted to evaluate the symptoms of endophthalmitis. Polymorphonuclear cells and tumour necrosis factor alpha (TNF-α) in aqueous fluid were measured at 0h, and 1, 2, 3, 7 and 15days. A histology test was conducted at 15days. B-mode ultrasonography and histology revealed that groups B and C had less inflammation than group A at 15days. Groups B and C had fewer polymorphonuclear cells and lower levels of TNF-α in aqueous fluid than group A at 2, 3 and 7days (P < 0.05). There was no significant difference between groups B and C (P > 0.05). There was no significant difference between groups A, B and C at 15days (P > 0.05). As an adjunct to vancomycin therapy to treat S. epidermidis endophthalmitis, LLLT has an antiinflammatory effect similar to that of dexamethasone.

Energy transition between Y b3+ - Tm3+ - Gd3+ in Gd3+, Y b3+ and Tm3+ Co-doped fluoride nanocrystals

YF3: 20% Gd3+, 20% Y b3+, 0.5% Tm3+ nanocrystal has been synthesized by a hydrothermal method. The upconversion (UC) emission and energy transfer progresses between Gd3+- Y b3+- Tm3+ under a 980-nm continuous wave semiconductor laser diode excitation have been explored. The experimental results show that the violet and ultraviolet (UV) enhancement with Tm3+ upconversion emission occurs in the nanocrystal, and in the same time the UC emissions of Gd3+ from 6D9/2, 6IJ, 6P5/2, and 6P7/2 states to the ground state 8S7/2 are obtained, too. The dynamic analysis implies that, under 980-nm excitation, the nanocrystal dimension plays a key role in the efficient energy transfer processes between Gd3+- Y b3+- Tm3tt based on the energy matching conditions.

Evaluation of Oxygen Consumption of Culture Medium andIn VitroPhotodynamic Effect of Talaporfin Sodium in Lung Tumor Cells

Successful photodynamic therapy (PDT) requires high production of radical ions and singlet oxygen to kill target cells. However, PDT also induces angiogenesis through production of vascular endothelial growth factor (VEGF), which promotes cell regrowth and vascularization. In this study, we evaluated the importance of oxygen in PDT by measuring oxygen consumption, photosensitizer bleaching, and reactive oxygen species (ROS) production in the culture medium, and VEGF secretion either during or after PDT treatment using mouse Lewis lung carcinoma (LLC) cells. Local hypoxia is induced under a low oxygen environment. Oxygen is consumed when ROS and singlet oxygen are produced during PDT. The effect of oxygen consumption on cytotoxicity and VEGF secretion has not been clarified. Mouse Lewis lung carcinoma (LLC) cells treated with the photosensitizer talaporfin sodium were irradiated by a continuous wave semiconductor laser (wavelength, 664 +/- 1 nm). We used oxygen microelectrode for oxygen measurement, a fluorescent probe to detect ROS, MTT assay to evaluate the PDT efficacy, and enzyme-linked immunosorbent assay to measure VEGF concentration. During PDT, oxygen consumption was higher with high doses of talaporfin sodium solution compared with low doses. In addition, the fluorescence of 2-[6-(4'-amino)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid, a probe for highly reactive oxygen species such as hydroxyl radicals (*OH), dramatically increased when the dose of talaporfin sodium solution was high. Moreover, VEGF concentration increased after PDT due to hypoxia in a manner dependent on photosensitizer concentration. These results indicate that the efficiency of PDT might be improved by sustaining a replete oxygen environment during PDT, not only for ROS and singlet oxygen production, but also for inhibiting neoangiogenesis.

Measurement of second-order nonlinear optical susceptibility of cBN crystal synthesized at high pressure and high temperature

We demonstrate a transverse electro-optical modulator based on a tiny and irregular octahedral wafer of cubic boron nitride (cBN) crystal that is prepared by hexagonal boron nitride at high pressure and high temperature using nitride as the catalyst. A continuous wave semiconductor laser at the wavelength of 650nm is used as a light source. A novel electrode fabrication is designed, a developed method different from the conventional transverse electro-optical modulator is introduced and the expression of the intensity of output beam is thought over. We obtain the half-wave voltage based on experiments of transverse electro-optical modulation. The second-order nonlinear optical susceptibility χijk(2)(ω,0)=1.919×10−12m/V of cBN crystal is calculated by means of the half-wave voltage.

Low-resistance p-type ohmic contacts for high-power InGaAs/GaAs-980 nm CW semiconductor lasers

In this paper, the optimization of ohmic contacts for semiconductor lasers based on InGaAs/GaAs/GaAlAs layers is reported. Transmission electron microscopy (TEM) and electrical methods were used to study extensively the Pt/Ti/Pt/Au metallization system. The contact fabrication technology was optimized towards achieving the lowest electrical resistance. The technological control and optimization concerned the contact annealing temperature and thickness of metallic layers that form the contact. The average specific contact resistance was below 5×10 −6 Ω cm 2 (with the record value of 8×10 −7 Ω cm 2) for the 10 nm Pt/20 nm Ti/30 nm Pt/150 nm Au system. The presented system was used in fabrication of continuous wave (CW) operated laser diodes. The chips mounted on passively cooled copper block achieved optical powers over 1 W, threshold current density values of 140–160 A/cm 2 and differential efficiencies above 1 W/A. The value of the characteristic temperature T 0 for discussed lasers varied in the range of 180–200 K.

Optical Phase Locking techniques: an overview and a novel method based on Single Side Sub-Carrier modulation

A short overview on Optical Phase locking techniques and a detailed description of the Phase Locking technique based on Sub-Carriers modulation is presented. Furthermore, a novel Single Side Sub-Carrier-based Optical Phase Locked Loop (SS-SC-OPLL), with off the shelf optical components, is also presented and experimentally demonstrated. Our new method, based on continuous wave semiconductor lasers and optical single side sub-carrier modulation using QPSK LiNbO(3) modulator, allows a practical implementation with better performance with respect to the previously proposed OPLL circuits, and permits an easy use in real time WDM signal coherent demodulation.