Green Laser Diodes Research Articles

Improving thermal stability of InGaN quantum wells by doping of GaN barrier layers

Thermal instability of InxGa1−x N quantum wells (QWs) is an obstacle to construct efficient blue and green LEDs and laser diodes. Structural degradation of QWs with indium content above 15% becomes severe at temperatures above 930 °C leading to formation of extended non-radiative areas within the active region. Our previous studies (Smalc-Koziorowska, 2021) indicated a relationship between the degradation process and metal vacancies present in the layers adjacent to the QWs. In this work, we show a method to overcome this problem by using heavy Si doping of the GaN barrier layers. In particular, such barrier layer grown on the top of n-type GaN layer below the InGaN QWs can act as a diffusion barrier for vacancies. The presence of silicon atoms increases the energy barrier for gallium vacancies migration. This effectively reduces possibility of diffusion of gallium vacancies from the n-type layer to the active region. As a result, improved thermal stability of QWs was achieved and significant degradation was not observed up to temperatures of 980 °C in comparison to 930 °C for the undoped structure.

A Study Protocol for Assessing the Effect of Diode Green Photocoagulation with Rose Bengal in Progressive Infectious Keratitis

Background: Infectious keratitis manifested as corneal ulcer can result in formation of pus in corneal tissue. The incidence has increased in recent years due to overuse of steroids. Infectious keratitis is the most common cause of blindness in India. Rose Bengal proves to be a promising option to treat this condition. Rose Bengal is topical ophthalmic dye which is mildly toxic. It is absorbed by damaged epithelial cells, mucus and fibrous cells. This stain is available in the form of 1% solution or impregnated filter strips. This study aims to assess the duration of resolution of corneal ulcer after Rose Bengal photodynamic therapy.
 Methodology: This will be an experimental study carried out at ophthalmology department of AVBRH, Wardha. Total 55 cases will be enrolled and examined on daily basis for one week. Pachymetry and specular microscopy will be done before Rose Bengal Photodynamic Therapy and at the end of three months of treatment.
 Results: Resistant infectious keratitis is expected to show complete healing of epithelial defect after receiving photodynamic therapy with green diode laser.

High-efficiency circularly polarized green light emission from GaN-based laser diodes integrated with GaN metasurface quarterwave plate

We demonstrated high efficient circularly polarized emission from the InGaN/GaN quantum well green laser diode (LD) integrated with GaN metasurface quarterwave plates. Optical properties of the nanoscale thin GaN nanograting metasurface were numerically studied and optimized for a quarter-wave plate. The fabricated nanogratings then were integrated on the emission facet of the LD. Both conversion efficiency and the polarization state of the device were measured, and the conversion efficiency is around 80% while the degree of circular polarization is maintained around 0.99. Our results of achieving a high degree of polarization and a high conversion efficiency at the integrated LD device pay the way for multi-functional applications in bio-imaging, submarine optical communication, quantum communication, and holographic display.

An injection‐locked green InGaN diode laser

AbstractWe designed a single‐frequency green laser system that can deliver a 60‐mW frequency‐tunable single‐longitudinal‐mode laser beam, having a 6.5 MHz linewidth at around 519 nm. An external cavity diode laser can provide a wavelength‐tunable single frequency laser beam, but its output power is limited. Therefore, an injection‐locked laser was designed with a Fabry–Perot type green InGaN laser diode in an external Littrow‐type cavity as the master laser and another laser diode of the same model as the slave laser. Injection locking can effectively enhance the output power and narrow the linewidth of the master laser. We found that the injection locking occurred at longitudinal mode matching between the master laser and slave laser diodes, which is located at a specific frequency for a periodical applied current. The side peaks of the injection locking due to the transverse mode mismatching were recorded and analyzed.

Greatly suppressed potential inhomogeneity and performance improvement of c-plane InGaN green laser diodes

激光显示、医疗设备及量子通信迫切需求高性能GaN基绿光激光二极管(LD). 研制绿光LD最大的挑战是生长高势能均匀性的InGaN/GaN多量子阱. 我们采用各种光学测量手段对绿光LD结构和芯片进行了表征. 在激发功率密度为7 W cm−2时, 300 K下光致发光半高宽为108 meV, 电流密度为20 A cm−2时, 电致发光半高宽为114 meV, 这些研究结果表明势能均匀性得到了显著改善. 同时, 由变温光致发光测试得到的表征局域态分布宽度的σ值和由时间分辨光致发光测试得到的表征激子局域带尾态的E0值都很小, 进一步表明势能均匀性很好. 由于势能均匀性的极大改善, 实现了斜率效率0.8W A −1, 输出光功率可以达到1.7W的绿光LD芯片.

Realization of 366 nm GaN/AlGaN single quantum well ultraviolet laser diodes with a reduction of carrier loss in the waveguide layers

The performance of ultraviolet (UV) laser diodes (LDs) with a low Al mole fraction AlGaN cladding layer was investigated by varying the thicknesses of the waveguide layer. It is found that (1) the loss of carriers in the waveguide layer is much larger than that in blue or green LDs due to the shallower quantum well and consequently a weaker carrier confinement of UV lasers. (2) Carrier loss in the waveguide layer can be suppressed by using a thinner waveguide layer. Therefore, the threshold current of LDs can be reduced. (3) The ultraviolet GaN/AlGaN single quantum well laser diodes lasing at 366 nm are fabricated by using relatively thin AlGaN waveguide layers and low Al mole fraction AlGaN cladding layers.

Epitaxial growth of 2.5-μm quaternary AlInGaN for n-cladding layer in GaN-based green laser diodes

The ridge morphology, which is related to random atomic step meandering, appears in thick AlInGaN films grown by metal organic chemical vapor deposition on both GaN templates and free-standing GaN substrates; this can be primarily attributed to the in-plane compressive strain in the thick layer. Therefore, a 2.5-μm Al0.08In0.0123GaN film with a slightly tensive strain was grown, with a regular and smooth step-flow morphology; the root mean square deviation of the film (with a size of 5 μm × 5 μm) was 0.56 nm.

Investigating the structural morphology, linear/nonlinear optical characteristics of Nd2O3 doped PVA polymeric composite films: Kramers-Kroning approach

This research presents a novel optical polymer of polyvinyl alcohol (PVA), as a host matrix, doped with various weight concentrations of Neodymium oxides (Nd2O3) metals, as a filler, where Nd2O3/PVA polymeric thin films were synthesized to be successfully utilized as a dynamic media for polymeric lasers. The solution casting method, simple and low-cost, was applied to homogeneously prepared composite films of Nd2O3-doped PVA. The crystallinity of the structures, the uniformity of the films, and the interactions among the Nd2O3 doping metals and the PVA matrix were approved via x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The remarkable effects of various weight concentrations of Nd2O3 doping on the optical parameters for Nd2O3/PVA composite polymeric thin films were determined using a UV–vis spectrophotometer. Kramers-Kroning’s approach was exploited to evaluate the linear refractive index (n), energy bandgap (E g ), and nonlinear optical effects for the proposed polymers.Moreover, a manual Z-scan method was applied to study the optical limiting effects using red He-Ne laser and green diode laser. This study illustrated some advantages of the outcome of the semi-crystalline structure, amazing linear optical parameters, including low optical energy bandgaps, brilliant dielectric constant, substantial optical limiting, as well as excellent nonlinear optical parameters of the proposed Nd2O3/PVA nanocomposite films. Thus, it is possible to conclude that the synthesized Nd2O3/PVA polymeric films play central roles in different promising, practical optoelectronic applications, such as lasers, optical filters, optical communication, light-emitting diodes, and optical switching.

Theoretical analysis of a high efficiency blue-laser-diode-pumped Ti:sapphire laser by high intensity pumping

We report on an efficiency increase for blue laser diode (LD) pumped continuous-wave (CW) Ti:sapphire lasers. We theoretically analyzed our experimental results and previous research and clarified the reliability of our theoretical model. Furthermore, we analyzed the optical-to-optical conversion efficiency of blue LD pumped CW Ti:sapphire lasers by using this theoretical model. As a result of the analysis, we found that the highest efficiency of 22.4% could be achieved with blue LD pumped CW Ti:sapphire lasers by using high intensity pumping and through our optimizations. To the best of our knowledge, this efficiency reaches the equivalent efficiency of the highest efficiency of green LD pumped CW Ti:sapphire lasers. According to previous research, improving blue LD pumped Ti:sapphire laser efficiency is challenging. Nevertheless, our analysis clarified that efficiency increases for blue LD pumped CW Ti:sapphire lasers can be achieved.

6.1: Invited Paper: Red, Green and Blue Laser Diodes and their Applications

In recent years, Laser Diode have been used in various applications. Initially, Infrared and Red Lasers began to be used for optical desks and optical communication applications. Blue‐Violet Laser was developed and adopted for Blu‐ray Disc. Since then, Blue and Green Lasers have been developed and Viable Laser Diode have begun to be used for various Display applications. This paper introduces the Laser Diode that have been developed so far, their applications, and various Display applications that are expected in the future.

Microstructure analysis and nonlin­ear/linear optical parameters of polymer­ic composite fil­ms based PVAL for wi­de optical applicati­ons

New proposed optical polymeric systems of PVAL/Cu particles have been synthesized by casting proceed to stand their NL (Nonlinear)/L (Linear) optical properties for various optical applications. Herein, the structure of the composites with various wt% of Cu was analyzed by the diffraction of X-ray (XRD) and FTIR. The semi-crystalline nature of PVAL has been influenced by Cu concentration as presented in XRD and Gaussian fitting. FTIR results confirm the strong interaction between Cu and polymer via the main hydroxyl group of the matrix. The morphological surfaces of pristine and doped PVAL have been measured. Optical measurement shows a redshift of the absorption edge. Moreover, the indirect transition bandgap decreased gradually with the Cu-level. This reflects the presence of localized states in the prohibited band facilities the electrons transition from HOMO to LUMO. The extinction coefficient and Urbach energy of the films have been enhanced. The ε o (static) and ε ∞ (high-frequency) dielectric variables are calculated. NL/L refractive index and susceptibility are estimated from the bandgap values. The optical limiting of the composite films has been tested using a green diode laser and He-Ne laser. The PVAL sample with high Cu wt% is an optical system capable of different technical applications, such as solar cells, optoelectronic devices, electronic apparatus, and optical filters.

Bidirectional White-Lighting WDM VLC–UWOC Converged Systems

A bidirectional white-lighting wavelength-division-multiplexing (WDM) visible light communication (VLC)-underwater wireless optical communication (UWOC) converged system with an office-level white light illumination of 514 lux and a symmetric downstream/upstream data rate of 150 Gb/s is demonstrated successfully. Red, green, and blue (RGB) laser diodes with two-stage light injection and optoelectronic feedback schemes are operated to provide bidirectional acceptable office-lighting and high-transmission-rate. White light is created/separated by combining/dispersing RGB lights utilizing two cascaded transmission gratings at the transmitting/receiving side. By employing PAM4 modulation and RGB triple-light WDM technique, the transmission rate is enhanced remarkably to 150 Gb/s for downlink/uplink transmission. Acceptable office-lighting (>500 lux) is attained through 3 m plastic optical fiber transport. Additionally, good bit error rate performance of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> and accepted PAM4 eye diagrams are obtained over 10 m free-space transmission with 5 m ocean underwater link. The bidirectional white-lighting WDM VLC-UWOC converged system demonstrated here is beneficial for the development of white-lighting with high-speed optical wireless communications.

Structural characterization and optical properties of nanostructured indium (III) phthalocyanine chloride/FTO thin films for photoelectric applications

In photoelectric applications, indium chloride phthalocyanine (InClPc) films are used. However, these films have not been extensively studied. The deposition of InClPc films on cleaned fluorine-doped tin oxide (FTO) substrates was achieved by the thermal vacuum evaporating technique. The structure and morphology of the InClPc/FTO sample were checked by X-ray diffraction and atomic force microscopy. It was found that the films consist of fine particles with spherical structures dispersed across the surface with the grain size increased from 79 to 126 nm as film thicknesses increase from 48 to 137 nm, respectively. The linear optical constants of InClPc films are extracted from spectroscopy of reflectance and transmittance in the wavelength range of 250−2500 nm. The InClPc films have two energy gaps with values of Eg1 = 1.37 eV and Eg2 = 2.84 eV, which slightly change with the effect of thickness. According to Miller's law, nonlinear optical parameters were evaluated. Two separate laser sources (red He-Ne laser and green diode laser) were used for the optical limiting testing. As well as the red He-Ne laser power intensity performance is high.

Rhodamine-6G organic films for optical limits: structural analysis, surface morphology, linear and nonlinear optical characteristics

Rhodamine dyes have been used as a sensor and nonlinear optical materials. Rhodamine 6G (Rh6G) film has been deposited onto glass substrates by the spin coater system. The structural investigation using X-ray diffraction displayed that Rh6G films have an amorphous structure. The surface morphology by atomic force microscopy showed that Rh6G films have nanostructure with a grain size of 159 nm for the thickness of 125 nm, which slightly increased to 166 nm for the thickness of 304 nm. The indirectly allowed transitions with three energy gaps were evaluated to be 1.91, 2.86, and 3.68 eV for the thickness of 125 nm, which changed to 2.02, 2.96, and 3.68 eV for the thickness of 304 nm. Also, the nonlinear refractive index and third-order nonlinear susceptibility were estimated. Two different types of laser stud the response of Rh6G films as optical limiters. The reaction of Rh6G films is highly influential for the laser power attenuating of the green diode laser at 533 nm, and He–Ne laser at 632.8 nm indicated that probably a member for diverse nonlinear optical applications such as CUT-OFF laser filters.

Effect of Photothermal Therapy with Indocyanine Green in Multispecies Biofilm

The purpose of this study is to investigate the antibacterial effects of indocyanine green (ICG) and near-infrared diode lasers on multispecies biofilms. Multispecies biofilms of &lt;i&gt;Streptococcus mutans&lt;/i&gt;, &lt;i&gt;Lactobacillus casei&lt;/i&gt; and &lt;i&gt;Candida albicans&lt;/i&gt; were treated with different irradiation time using photosensitizer ICG and 808 nm near-infrared diode laser. Colony forming unit (CFU) was measured, and qualitative evaluation of biofilm was performed with confocal laser scanning microscopy (CLSM). Temperature measurement was conducted to evaluate photothermal effect. In the groups using ICG and diode laser, reduction in CFU was statistically significant, but the difference in antibacterial effect on &lt;i&gt;L. casei&lt;/i&gt; and &lt;i&gt;C. albicans&lt;/i&gt; with irradiation time was not significant, and similar results were confirmed with CLSM. Groups with ICG and diode laser showed higher temperature elevation than groups without ICG, and results of measured temperature were similar to the range of hyperthermia. In conclusion, ICG and near-infrared diode laser showed antibacterial effects on multispecies biofilms, but studies on protocol are necessary for clinical application.

Structure analysis and nonlinear/linear optical properties of PVAOH/Si composites for low-cost optical technologies and limiting absorption

Optical limiting is considered one of the significant unusual applications that attract the attention of many scientists. In this study, we synthesized a novel flexible composite of silicon (Si)-doped polyvinyl alcohol (PVAOH) for this purpose. The preparation of the present polymeric film with different Si weight percentage was prepared by casting technique. The X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis spectroscopy of X-rays (EDX), and Fourier-transform infrared spectroscopy (FTIR) have been carried out. Also, UV–Vis–NIR spectroscopy has been used to test the optical interpretation of the as-prepared films. The analysis of the structure reveals substantial integration between the two current phases. The SEM images created to the samples indicate an increase in surface roughness with the Si- substantive. The addition of Si to the virgin PVAOH has an impact on the optical properties such as the indirect optical energy gap (Eg), the arrangement of the localized state (Eu), absorption coefficient, and optical conductivity response. Depending on different models like Moss, Herve–Vandamme, Ravindra, and Singh-Kumar, the relation between the refractive index and the energy gap has been explored. Besides, the linear together with nonlinear optical assets of PVAOH/xSi polymer composites were investigated. The limiting aspects of the sample absorption were explored by employing different wavelengths (635 and 532 nm) coming from the He–Ne and green diode laser sources. The PVAOH/0.1Si film revealed significant optical advantages along with high optical laser limitation, recommending this could be a petitioner for different nonlinear technological devices and laser shields.

Characteristics of InGaN-based green laser diodes with additional InGaN hole reservoir layer

The injection of holes has an important impact on the performance of InGaN-based green laser diodes (LDs). In this work, we propose a new structure with InGaN hole reservoir layer (HRL) inserted between the last quantum barrier and the upper waveguide to improve the hole injection. It is found that the hole injection current is significantly increased due to the reduction of the hole effective barrier height. Furthermore, lower threshold current and higher output power are obtained, and the optical field leakage is effectively suppressed. Besides, the influences of thickness and In composition of the HRL are also investigated. It is more favorable to improve the properties of LDs when the HRL has a quite low-In content and a thickness of only nearly 11 nm.

Mode Locking of Dye Laser Pumped by Current-Modulated Green Laser Diodes

We report the mode locking regime of dye laser pumped by 400 ns laser diode pulses. Three green laser diodes operating at 513 nm are used as the pump source. We obtain subnanosecond pulse trains using periodic 1 ns pulse modulation of the power-supply current through the pump diodes. The addition of a saturable absorber results in both a decrease in the pulse duration to 0.2 ns and a good reproducibility of the output radiation..

Effect of thickness on structural and optical characteristics of Indium Phthalocyanine Chloride thin films for photodiode devices

Indium phthalocyanine chloride, InPcCl, in the form of thin films were prepared with different thicknesses by thermal evaporation technique. X-ray diffraction showed a hump at 2θ = 28°, which identified that the prepared InPcCl films have an amorphous structure. The particle size increased from 56 to 357 nm with increased film thickness as indexed by Atomic Force Microscope technique. The transmittance and reflectance spectral distribution of InPcCl films was measured through a range of 250–2500 nm of wavelength. The optical transition is indirectly allowed with two optical energy gaps (Eg1 = 1.37 eV and Eg2 = 2.84 eV) for InPcCl thin films, which are smaller than other phthalocyanine films. The dispersion parameters were calculated for the different film thickness of InPcCl films from refractive index analysis in the region of normal dispersion. The linear, third-order, non-linear refractive index and non-linear susceptibility have also been measured. The optical limiting response was evaluated for the InPcCl films under the He–Ne laser and a green diode laser. The InPcCl film of thickness 95 nm exhibits the highest output power values and the normalized power. This advanced result will hopefully apply to the field of photodiode devices in an industrial approach.

Influence of indium composition of n waveguide layer on photoelectric performance of GaN-based green laser diode

Influence of indium composition of n waveguide layer on photoelectric performance of GaN-based green laser diode