Blue Laser Diodes Research Articles

67‐2: Adoption of Blue Light Semiconductor Laser Diode (BLDA) in LTPS TFT Manufacturing

We have investigated adoption of CW blue laser diode annealing (BLDA) in manufacturing process of LTPS TFT backplane. Our experiments have shown that except crystallization annealing, BLDA can be adopted in dehydrogenation of precursor amorphous silicon film, and also can be used in the activation after ion implantation. By using BLDA dehydrogenation of H2 content as high as 20% can be implemented. In the activation, BLDA can achieve surface resistance much lower than using conventional RTA.

Speckle- and interference fringes-free illumination system with a multi-retarder plate.

Our study proposes a novel method for obtaining speckle-free homogeneous illumination using a combination of a multi-retarder plate, a microlens array, a Fourier lens, and a diffraction optical element (DOE) based on pseudorandom binary sequences. The proof-of-concept multi-retarder plate is introduced to generate multiple uncorrelated laser beams, while a mathematical model was developed to explain the method's mechanism and evaluate its effectiveness. In the DOE passive (stationary) mode, the method was found to reduce speckle contrast to 0.167, 0.108, and 0.053 for red, green, and blue laser diodes, respectively. In active mode, the speckle contrast was further reduced to 0.011, 0.0147, and 0.008. The observed differences in speckle contrast in the stationary mode were attributed to variations in the coherence lengths of the RGB lasers. By implementing the proposed method, we successfully generated a square-shaped illumination spot that was free from interference artifacts. The spot obtained exhibited a slow, weak variation in intensity across the screen, attributable to the multi-retarder plate's suboptimal quality. However, this limitation can be readily addressed in future studies through the adoption of more advanced fabrication techniques.

Simple and compact high-power continuous-wave deep ultraviolet source at 261 nm based on diode-pumped intra-cavity frequency doubled Pr:LiYF4 green laser.

We report the recent progress on diode-pumped high-power continuous-wave Pr:LiYF4 (YLF) green laser and deep ultraviolet (DUV) laser generation via intracavity frequency doubling. Using two InGaN blue diode lasers as pump source to form a double-end pumping geometry, in this work, we have demonstrated a green laser at 522 nm with a maximum output power of 3.42 W, which is believed to be the highest power ever achieved in all-solid-state Pr3+ lasers in this specific spectral region. Moreover, by intracavity frequency doubling of the achieved green laser, we have further obtained a DUV laser at about 261 nm with a maximum output power of 1.42 W, which is far higher than previous results. The watt-level 261-nm laser paves the way towards the realization of simple and compact DUV source for a variety of applications.

Effectiveness of katuk leaf chlorophyll (Sauropus androgynus (L) Merr) with blue and red laser a ctivation to reduce Aggregatibacter actinomycetemcomitans and Enterococcus faecalis biofilm

In this study, the efficacy of using Sauropus androgynus (L) Merr, a katuk leaf chlorophyll photosensitizer, to reduce Aggregatibacter actinomycetemcomitans and Enterococcus faecalis biofilm was investigated. A red and blue diode laser is used as the light source. The sample was split into four groups: a negative control group, a positive control group, a blue laser treatment group (B), and a red laser treatment group (R), both with and without the addition of katuk leaf chlorophyll 1.6 mg/ml, and with varying densities of laser energy exposure of 2.5 J/cm2, 5 J/cm2, 7.5 J/cm2, and 10 J/cm2. Laser exposure and chlorophyll photosensitizer were tested using ELISA and ANOVA. At an energy density of 10 J/cm2, the optimal bacterial mortality rate was obtained in each treatment group. Namely, in the Aggregatibacter actinomycetemcomitans biofilm, the negative group, the number of deaths was 73.30% using a blue diode laser and 63.25% using a red diode laser. In the positive group, the number of deaths was 86.12% using a blue diode laser and 83.29% using a red diode laser. In the Enterococcus faecalis biofilm, in the negative group, the number of deaths was 67.78% using the blue diode laser and 75.33% using the red diode laser, and in the positive group, the number of deaths was 71.71% using the blue diode laser and 86.41 using a red diode laser. Exposure to blue and red diode lasers activates chlorophyll in katuk leaves, killing bacteria and reducing biofilms.

A new smart laser photoluminescent light (LPL) technology for the optimization of the on-street lighting performance and the maximum energy saving: development of a prototype and field tests

Lighting demand in built environments corresponds to more than 10% of the global energy use, with great potential for energy saving thanks to innovative smart materials and combination of passive–active strategies. This paper focuses on an innovative smart lighting system based on a blue-diode laser technology combined with photoluminescent pavements, to obtain a self-lighting surface with a substantial reduction in electricity consumption. A laser variable angle scanner prototype was developed and operated through a dedicated management software. The prototype was installed in lab to measure the emitted luminance/illuminance of the pavement, its time decay, and the electricity consumption. This application is yet a prototype, the scanning area and the investigated pavement are more compatible with pedestrian street and sidewalk because of the lower illuminances to be maintained. The results were compared to standard solutions installed in typical roads. The results presented promising benefits in terms of electricity saving (about 40% compared to standard LEDs) and luminance uniformity (higher than 0.9 compared to standard systems, i.e. 0.17÷0.33). Important future ideas derive from preliminary experimental campaigns to improve the smart laser system, and the coupled pavement properties to reduce the consumptions and improve the lighting conditions for pedestrians and vehicles, within potential self-lighting streets.

Laser-induced in situ synthesis of nano-composite Co–Co3O4–rGO on paper: miniaturized biosensor for alkaline phosphatase detection

Recent progress in the in situ synthesise of various nanomaterials has gained tremendous interest and wide applications in various fields. For the first time to the best of our knowledge, this work reports a methodology of ultra-fast in situ synthesis of cobalt–cobalt oxide-reduced graphene oxide (Co−Co3O4−rGO (CC–rGO)) composite by laser ablation. The photothermal reduction technique was leveraged to develop the CC–rGO. For this, a low-cost 450 nm blue diode laser was irradiated onto a grade 1 filter paper in the presence of cobalt ions readily patterns the carbon matrix of paper to the composite material. Moreover, the variation of cobalt concentrations from 0.1–0.5 M led to structural and morphological changes. Standard techniques were adopted for thorough characterizations of developed sensor material for conductivity analysis, specific surface area, crystal-structural information, surface morphology, and chemical composition. The observed results were highly promoting towards the electrochemical sensing applications. Further, the developed sensor was found to be highly selective toward detecting a vital bio analyte alkaline phosphatase (ALP). The sensors performance was highly significant in the linear range of 10–800 mU l−1 with a detection limit of 10.13 mU l−1. The sensors applicability was further validated in actual human serum samples via a recovery-based approach. In the future, the developed in situ material methodology can begin a rapid composite material synthesis at a larger scale.

Electron Trapping Optical Storage Using A Single‐Wavelength Light Source for Both Information Write‐In and Read‐Out

AbstractIn conventional electron trapping optical storage phosphor, both short‐ and long‐wavelength light are needed for information write‐in and read‐out, respectively, complicating the optical storage system. Here, a Y3Al2Ga3O12:Pr3+,Eu3+ optical storage phosphor with Pr3+ as an electron donor and Eu3+ as an electron trap is designed, and a single wavelength write‐read scheme is demonstrated, which employs the same blue laser diode (LD) light source for both optical write‐in through two‐photon up‐conversion charging and for read‐out based on photostimulated luminescence (PSL), originated from 4f15d1→4f2 transition of Pr3+ peaked at 315 nm in UV region. A deep electron trap with the mean depth of 1.42 eV and a narrow distribution of 0.3 eV is observed in the presence of Eu3+ in Y3Al2Ga3O12:Pr3+, implying its long‐term storage potential. The write‐in and read‐out experiments are conducted using 450 nm blue LD light with the power density of 1 W cm−2 for write‐in and that with a low power density of 0.02 W cm−2 for read‐out in order to avoid the effect of up‐conversion luminescence on PSL signal. These results will advance the electron trapping optical storage scheme.

20.4: Activation of Doped Silicon Film Using Semiconductor Blue Light Diode Laser Annealing

We have investigated activation annealing of the doped poly silicon film of LTPS TFT by using CW semiconductor blue light diode laser. It has been found that by full melting and re‐crystallization, the sheet resistance can be reduced significantly to 1/3 of which can be realized by using conventional RTA treatment. We will report the experiment results in the paper.

Pump Excited-State Absorption at 442 ± 1 nm for Efficient Visible Fluoride Fiber Lasers

In the well-known excited-state absorption (ESA) process, population inversion of the laser transition can be achieved by a strong pump ESA involving a lower laser level. The exploitation of pump ESA has expanded from the visible to the near-infrared spectral range, based on various laser sources. Extending the operating wavelength of the pump ESA is greatly significant for the development of rare-earth-doped fluoride fiber lasers. Herein, we report, presumably, the shortest operating wavelength of pump ESA at 442 ± 1 nm for an efficient continuous-wave visible fluoride fiber laser. A novel scheme for direct blue diode pumping was proposed and demonstrated in an Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped fluoride fiber. Utilizing a 442 ± 1 nm blue laser diode, single-wavelength ground-state absorption (GSA) and ESA pumping mechanism were investigated not only for double populating of the upper laser level by GSA and ESA, but also to depopulate the lower laser level by ESA. We report a slope efficiency of 50.3% with respect to the launched pump power of 442 ± 1 nm and an output power of up to 327 mW for a 750 nm fiber laser. This result is an order of magnitude higher than that previously reported for a directly blue-diode-pumped deep-red Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped fluoride fiber laser. Moreover, the numerical modeling results were in good agreement with the experimental results. Our approach represents a significant advancement for blue pump ESA in visible fluoride fiber lasers, which opens new capabilities for blue-diode pumping for a wide range of future applications.

Vigorous high-efficiency YAGG:Ce phosphor-in-glass film for next-generation laser lighting applications

It is an important challenge to select suitable color converters and apply them to laser diodes (LDs) lighting field. Sapphire plates are used as substrates for phosphor-in-glass films (PiFs) due to their ultrahigh thermal conductivity (∼ 30 W m−1 K−1). Herein, Y3Al3.5Ga1.5O12:Ce3+ (YAGG:Ce) phosphor mixing silicate glass powder is successfully sintered on sapphire plates to fabricate YAGG:Ce phosphor-in-glass film (PiF). The microstructure appearance and photoelectric characteristics of the efficient green color converter are studied in detail. In addition, it is worth noting that the maximum internal quantum efficiency of the prepared PiF is 92%, which is close to that of the original phosphor (98%). Meanwhile, the saturation threshold of YAGG:Ce PiF reaches 38.96 W/mm2 with luminous efficiency (LE) of 230.85 lm/W under the excitation of 460 nm blue LD. Notably, PiF has ultra-high power density while still maintaining such high LE. In order to highlight the application of this color converter in laser lighting, we assemble laser flashlights and fireflies lights. The test of the laser flashlight shows excellent performances such as high brightness, strong focusing effect and wide irradiation range. All indications manifest that YAGG:Ce PiF is an excellent green color converter.

Composition and luminescence properties of highly robust green-emitting LuAG:Ce/Al 2O 3 composite phosphor ceramics for high-power solid-state lighting

The major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance. However, phosphors usually suffer laser-induced luminescence saturation, which limits the peak luminance of laser lighting devices. The aim of the present study is to develop LuAG:Ce/Al₂O₃ composite ceramics (LACCs) with a high saturation threshold for high-luminance laser lighting. Owning to the rigid crystal structure, proper synthetic process, and optimized thermal design, the LACCs possess small thermal quenching (16% loss in luminescence at 225 ℃), high quantum yield (&gt; 95%), and excellent luminescence properties. When the LACCs are irradiated by blue laser diodes in a reflection mode, a high luminous flux of 4634 lm and luminous efficacy of 283 lm·W⁻¹ are realized. Furthermore, they show no sign of luminescence saturation even when the power density reaches 20.5 W·mm⁻². With these favorable properties, the designed LACCs show great potential in high-luminance laser lighting.

Antibacterial potential of riboflavin mediated blue diode laser photodynamic inactivation against Enterococcus faecalis: A laboratory investigation.

This study aimed to evaluate the inactivation potency of riboflavin-mediated blue diodelaser photodynamic inactivation (PDI) against Enterococcusfaecalis at planktonic and biofilm stages and also investigated itseffect on the tooth color change. The antibacterial and antibiofilm activities of riboflavin mediated PDI against E.faecalis were investigated. The numbers of colony-forming units (CFUs)/mL were calculated. Teeth discoloration were evaluated using the CIE L*a*b* based color difference (ΔE). Antibacterial analysis indicated that the blue diode laser irradiation at 12, 18, 24, and 30J/cm2 alone and different concentrations of riboflavin solution (6.25 to 100μM) reduced the number of CFU/mL of E.faecalis, but the reduction was not statistically significant (P>0.05). Depending on the riboflavin concentration and the light dose, there can be as much as a 1-log effect on CFU/mL. In addition, E.faecalis biofilmwas more affected with 30J/cm2 irradiation dosage and 100μM riboflavin than other groups. Meanwhile, bacterial suspensions treated with 5.25% sodiumhypochlorite (NaOCl) showed maximum biofilm inhibition and colony number reduction, compared with the control. The teeth exhibited clinically acceptable color change after riboflavin treatment at concentrationranging from 6.25 to 50μM (ΔE < 3.7). The riboflavin mediated PDI process is somewhat less effective than NaOCl but perhaps less toxic to tissues. It might be feasible to repeat the riboflavin+light treatment to further promote efficacy.

Screening of Broadband Near-Infrared Cr3+-Activated Phosphors Using Ce3+ as a Probe

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are ideal miniaturized NIR light sources, but it is still difficult to find broadband-emitting NIR phosphors due to the lack of appropriate material design principles. In this work, we propose a method to find hosts yielding broadband NIR Cr3+ emission by screening Ce3+-doped phosphor hosts for which both Ce3+ and Cr3+ can occupy the same crystallographic site. A NIR phosphor Ba3Sc4O9:Cr3+ (BSO:Cr3+) with an emission peak at 835 nm and a full width at half-maximum (FWHM) of 188 nm is obtained, where Ce3+ or Cr3+ is accommodated at the same Sc3+ site. The BSO:Cr3+ ceramic is demonstrated to produce a NIR emitter with an output power of 14.56 mW when driven by a blue laser diode at 5.0 V/100 mA. By following the proposed method, two broadband NIR phosphors composed of Li3Sc2(PO4)3:Cr3+ (λem = 1000 nm, FWHM = 223 nm) and Na3Sc2(PO4)3:Cr3+ (λem = 895 nm, FWHM = 184 nm) are further discovered.

Ambient Hydrocarbon Detection with an Ultra-Low-Loss Cavity Raman Analyzer.

The detection of ambient outdoor trace hydrocarbons was investigated with a multipass Raman analyzer. It relies on a multimode blue laser diode receiving optical feedback from a retroreflecting multipass optical cavity, effectively creating an external cavity diode laser within which spontaneous Raman scattering enhancement occurs. When implemented with ultra-low-loss mirrors, a more than 20-fold increase in signal-to-background ratio was obtained, enabling proximity detection of trace motor vehicle exhaust gases such as H2, CO, NO, CH4, C2H2, C2H4, and C2H6. In a 10-min-long measurement at double atmospheric pressure, the limits of detection obtained were near or below 100 ppb for most analytes.

Blue (0.44 µm) and red (1.7 µm) diode laser activated bleaching—dental shade changes determination

Tooth whitening or bleaching is one of the most common dental procedures that optimize the white color of the teeth and minimize the simultaneous damage to the tooth structure. Light can speed up the whitening process with halogen lamps, light-emitting diodes, plasma arc lamps, and lasers. Our results show that combinations of a teeth whitening agent with laser light irradiation with a 0.44 µm blue laser diode or a 1.7 µm near-IR laser diode accelerate the whitening process not only during tooth irradiation but also within two weeks after the procedure.

A Study on the Development of a White Light Source Module for a Large-Capacity Searchlight Using a Blue Laser Diode

In this paper, a large-capacity white light source module using a high-power blue laser diode and a reflective spaced phosphor was designed. The reflective spacing phosphor ensured thermal stability. The proposed white light module is a reflective phosphor structure with a bi-directional optical system based on a rhombus prism lens. The rhombus prism optical system can greatly narrow the blue laser beam width and a long-wavelength band-pass filter of 500 nm or more is applied to change the movement path of the laser beam and transmit white light excited by the phosphor. A dichroic filter was applied to the fold mirror part and a planar convex lens was designed to focus the blue laser beam so that the phosphor was irradiated. Finally, a high-power white light source is obtained from the pre-optics unit to which the dichroic filter is applied. In order to use the proposed white light source as a searchlight, a divergence angle of 4° or less is required. For this implementation, a large-area collimating lens combining an aspheric condensing lens and an achromatic lens was applied. It was confirmed that the divergence angle of 4 degrees or less was satisfied at the focal length (FL) of 38.5 to 42.5 mm of the optical lens of the laser white light module emitter and the collimating optical system.

Alexandrite lasers with blue-diode-pumping.

The availability of high-power and high-brightness blue diode lasers makes them attractive as low-cost pump sources for broadly tunable Alexandrite lasers. In this paper we investigate the performance of an Alexandrite laser pumped by a high-power fiber-delivered blue diode module. Output power 1.84 W is achieved, the highest power from blue diode pumped Alexandrite to date. Excellent pump absorption is demonstrated of scrambled pump polarization on both a-axis and b-axis of Alexandrite crystal. Wavelength tuning and dual wavelength operation is produced using the self-birefringent filtering of the Brewster-cut Alexandrite crystal. An analysis is made of laser efficiency and mode formation including the creation of higher-order Laguerre-Gaussian vortex modes (LG01 and LG02). Performance is compared to red diode pumping and prospects for further optimization and power-scaling are discussed.

High speed coating for pure copper by multi-beam laser metal deposition method with high intensity blue diode lasers

Copper is expected to have many applications due to its virus inactivation properties, but it has been difficult to produce a thin layer with high bonding strength. A multi-beam blue diode laser installed laser metal deposition (B-LMD) system was newly developed with a laser intensity of 4.7 × 105 W/cm2, which is improved about five times higher than that of conventional systems. Using this system, we demonstrated the high-speed formation of a pure copper layer on a stainless steel type 304 (SS304) circular tube. A pure copper powder and the blue diode lasers were simultaneously supplied to a SS304 circular tube, and the powder was melted and solidified to form a pure copper layer on it. As the result, the laser intensity was increased with increasing layer formation efficiency, and at the laser intensity of 4.7 × 105 W/cm2, the maximum value of layer formation efficiency was obtained at the peripheral speed of 400 mm/s. Moreover, it was revealed that the dilution length was decreased with increasing peripheral speed, the minimum value of 3 μm at the peripheral speed of 400 mm/s was obtained.

Polarization Doping in a GaN-InN System-Ab Initio Simulation.

Polarization doping in a GaN-InN system with a graded composition layer was studied using ab initio simulations. The electric charge volume density in the graded concentration part was determined by spatial potential dependence. The emerging graded polarization charge was determined to show that it could be obtained from a polarization difference and the concentration slope. It was shown that the GaN-InN polarization difference is changed by piezoelectric effects. The polarization difference is in agreement with the earlier obtained data despite the relatively narrow bandgap for the simulated system. The hole generation may be applied in the design of blue and green laser and light-emitting diodes.

Laser Cladding With Combined NIR and Blue Diode Laser Including In-Line Atomic Emission Spectroscopy

For Directed Energy Deposition processes (DED) lasers in the near infrared (NIR) as well as in the infrared (IR) range are predominantly used. Recent developments have also made high-power lasers in the visible spectrum available. As the DED process is used for cladding of surfaces, repairing and additive manufacturing of components, process monitoring and control methods are necessary to ensure a consistent manufacturing quality. Optical emission spectroscopy (OES) of the process radiation can provide information on process conditions and the deposition layer during DED processes. However, DED processes are in the heat conduction regime and superimposed broad spectral emissions dominate the wavelength specific signals. The object of this work is to compare the process behavior using a NIR and blue diode laser separately as well as in combination. The influence of the laser wavelength on the cladding result as well as on the emitted process radiation is to be determined. Therefore, single tracks of Co-based powder (MetcoClad21) were clad on an S235 base material by using each laser source separately as well as in combination. Both laser beams were combined within a single hybrid optic. While the scan speed and powder feed rate remained constant, the laser power was varied. Single spectra have been recorded from the process using a spectrometer. Single spectra are sorted and element lines were identified. Only non-ionised elements could be detected, with chromium appearing frequently. It was shown that comparable results in terms of cladding quality can be produced independently from the laser wavelength. In fact, less laser power (app. 30% less, 1 kW at 980 nm (NIR) compared to 0.7 kW at 450 nm (blue)) was needed aiming for comparable results in geometrical factors (as dilution, height, depth, width) and homogeneity (chemical composition distribution) by using blue laser irradiation. Furthermore, more spectrometric signals (approx. 2–28 times more) were detected compared to experiments using only NIR irradiation with the same laser power. This effect is particularly high at low laser powers and decreases with increasing power. Hence, it is possible to enable in-line process analysis by adding blue laser irradiation to the mix of the beam.