Blue Laser Diodes Research Articles

Laser-Induced Fluorescence Studies on Some Edible Oils and Aromatic Frankincense Oil Excited by Blue and Violet Diode Lasers at 447 nm and 405 nm

Laser-induced fluorescence (LIF) of certain edible oils (olive, mustard, sunflower, corn, sesame, peanut, rice bran, and flaxseed) and one unique aromatic oil (frankincense oil) have been studied using compact blue and violet lasers operating at 447 nm and 405 nm, respectively. LIF studies excited at these wavelengths have not been performed before, to our knowledge. The various features of the obtained spectra and their possible molecular origins have been discussed. The presence of vitamin E has been confirmed in corn, rice bran, peanut, sunflower, and frankincense oils, and the possible origin of the double peaks in the red region for olive oil has been explained.

High-efficiency yellow-emitting La3Si6N11:Ce phosphor-in-glass for laser-driven white lighting

To cope with the market competition of solid-state lighting, there is an urgent need for an efficient and stable fluorescent conversion material that can be used in high-performance lighting. A novel and unique nitride phosphor, La3Si6N11:Ce3+ (LSN), exhibits a wider luminescence spectrum and better thermal quenching performance than Y3Al5O12:Ce3+ (YAG). In this study, LSN phosphors are dispersed in a SiO2–B2O3–CaO–Na2O glass system, and a series of LSN phosphor-in-glass (LSN PiG) samples are prepared by a low-temperature co-sintering technique. The luminescence, thermal stability, microstructure and photoluminescence properties are investigated. The internal quantum efficiency of LSN:Ce PiG (85%) is close to that of the original phosphor (90%). Under excitation of a 450 nm blue laser diode, the LSN PiG produces white light with a luminescence efficiency of 145.91 lm/W, and a luminous flux of 209lm is achieved. Moreover, the color rendering index of LSN is much higher than that of YAG, reaching 73, indicating that LSN PiGs have good application prospects as yellow converters in high-power laser lighting.

Highly thermally stable red phosphor-in-glass films for high-power laser lighting

The development of CASN (CaAlSiN3: Eu2+) fluorescent materials with excellent quantum efficiency and low thermal quenching performance is an effective way to improve the quality of white light. In this research, a CASN-PiG film with a high external quantum efficiency (56%) and high thermal conductivity (12.935 W m−1 K−1) was prepared by co-firing CASN phosphors and glass powder on a sapphire substrate. The surface structure and optical properties of the CASN-PiG (phosphor-in-glass) film were studied in detail. Furthermore, the CASN-PiG film can even survive 5.3 W/mm2 blue laser excitation. Surprisingly, the blue laser diode is combined with the CASN-PiG film to obtain a high luminous flux of 164 lm. Importantly, the CASN phosphors is compounded with Ce:YAG phosphors to prepare a high CRI (85) PiG film with a luminous flux of 845 lm and a luminous efficiency of 190 lm/W, realizing high-quality white laser lighting.

Experimental demonstration of a transmitter with a 50° divergence angle, 50 Mbps rate, and 476 mW optical power for underwater wireless optical communication based on an engineered diffuser.

In practical application of underwater wireless optical communication (UWOC), the transmitter should have a larger divergence angle to make it easier to establish a communication link, besides high modulated rate and high optical power. Laser diodes (LD) are suitable to design such transmitter, thanks to their simpler structure and much faster switching speed. However, it is difficult to implement for widespread use in ocean engineering because of its quite small divergence angle. For this, we present a simple way to enlarge the divergence angle for an LD transmitter based on an engineered diffuser in this paper. First, we design a blue LD transmitter that has 476 mW output power, 50 Mbps rate, and 50° divergence angle. Then, using such transmitter, we establish a UWOC system in a large experimental tank with 13.3 m communication distance and about 0.26m-1 attenuation coefficient of water. The results show that if the deviation of the transmitting direction is up to ±25∘, the communication system is workable. Emission light from the transmitter could cover a 42.5% solid angle of the hemisphere space. The combination performances of speed, angular coverage, and optical power are suitable for ocean engineering. Also, it implies that a light field could be designed by using a suitable engineered diffuser for UWOC. The method presented in this paper is simple and pragmatic, which is useful to reduce the difficulty in establishing communication links and is easy to popularize.

Thermo-optical control of L-band lasing in Er-doped tellurite glass microsphere with blue laser diode.

Miniature lasers based on rare-earth ion-doped tellurite microsphere resonators with whispering gallery modes (WGMs) are promising devices for basic research and applications. However, the excitation of WGMs using an external pump is not a simple task requiring passive or active control. We propose and demonstrate the implementation of thermo-optical control of the L-band laser generation in an Er-doped in-band pumped tellurite glass microsphere using a cheap low-power blue laser diode and a constant-wavelength telecom laser as a pump. The proposed scheme ensures simplification and cost reduction of microlasers.

High efficiency green-emitting phosphor-in-glass films for high-power solid-state laser lighting

The next generation of solid-state lighting technology driven by laser diodes (LDs) is in full development, and the way green fluorescent materials with narrow-band emission (such as β-Sialon) exert their inherent potential in laser displays and projectors has attracted public interest. In this paper, stable borosilicate glass was utilized as an inorganic binder to prepare phosphor-in-glass films (PiFs) by cosintering sapphire and β-Sialon phosphor. There was no interface reaction between the glass and the phosphor, and the phosphor was uniformly and nondestructively distributed in the composite film closely attached to the sapphire. The optimized PiFs achieved an internal quantum efficiency of 76% and a thermal conductivity of 8.6 W m−1K−1, and a thermal diffusivity of 2.6 mm2 s−1 demonstrated their excellent thermal stability. A beam of high-purity light with a brightness of 887 lm and a luminous efficiency of 183 lm/W was achieved under 450 nm blue LD radiation, which is the relatively superior performance by β-Sialon series luminescent materials in an LD application reported thus far. We believe that in the near future, strategies such as adjusting glass composition, improving quantum efficiency, and sample postprocessing will further improve the performance of β-Sialon phosphors with narrow-band emission to make new contributions in the field of high-quality lasers.

Speckle free efficient light engine for high power laser projectors and automobile headlamps

Laser speckles and spurious fringes are the major obstacles in the development of emerging technologies relating to laser-based projection imaging and illumination. It becomes more challenging when such systems employ high-power lasers, such as laser-based cinema projectors or laser-based automobile headlamps. Addressing such challenges, we report a compact design and step-by-step development scheme of a laser speckle reduction system in this article. The method comprises a metallic ball-mirror connected with the mechanically dynamic and thermally conductive heat sink. The ball-mirror was highly reflecting and coated with a transparent thick film of ZnO nanoparticle embedded epoxy adhesive that provides volume scattering of a highly directional laser beam. Epoxy layer were further diffused by sandblasting to achieve surface scattering of the laser light. The combined effect of volume and surface scattering were utilized to produce spatial diversity, while the temporal diversity was achieved by the rotation of ball-mirror diffuser system. Spatial and temporal diversities are the fundamental speckle reduction techniques that become more efficient when they are employed with a tiny pyramidal reflective cavity. TracePro simulations demonstrate the efficiency enhancement in the system due to the involvement of a pyramidal reflector for three primary wavelengths (RGB). Qualitative results of the light-scattering for red, green, and blue lasers and the quantitative results of speckle contrast are reported. Speckle contrast reduction was experimentally achieved by 0.0248 for red, 0.0298 for green, and 0.0213 for blue laser diodes.

Electrically injected GaN-on-Si blue microdisk laser diodes.

III-nitride blue microdisk laser diodes are highly desirable in emerging applications, such as augmented reality, virtual reality, and visible light communication. However, the electrically pumped blue microdisk lasers have been lagging for decades owing to weak optical confinement and large internal absorption loss. In this study, the waveguide layers and cladding layers were carefully engineered to enhance the optical confinement and reduce internal absorption loss. Therefore, the first electrically injected blue microdisk laser diodes grown on Si substrates have been successfully fabricated, and exhibited a resistor-capacitance-limited bandwidth of 24.1 GHz, showing highly promising applications in high-speed and large-modulation-bandwidth visible light communication.

Ultra‐Efficient GAGG:Cr3+Ceramic Phosphor‐Converted Laser Diode: A Promising High‐Power Compact Near‐Infrared Light Source Enabling Clear Imaging

AbstractNear‐infrared (NIR) light is widely used in fields such as organic components detection and biological imaging, due to its strong tissue penetration and non‐destructive characteristics. To improve the detection sensitivity and spatial resolution of bioimaging, it is important to obtain a new NIR light source with good thermal stability, high efficiency, and ultra‐high optical output power, which currently remains a great challenge. In view of this, a Gd3Al2Ga3O12:Cr3+(GAGG:Cr3+) NIR ceramic phosphor is proposed in this study. By optimizing the preparation process of GAGG:Cr3+ceramic phosphor and the concentration of Cr3+ions, high external quantum efficiency (EQE = 70.1%) and excellent thermal stability (96.8%@150 °C) are achieved. After coupling the GAGG:Cr3+ceramic phosphor with a blue light‐emitting diode (LED), the electro‐optical conversion efficiency of the NIR ceramic phosphor converted LED (NIR‐cpc‐LED) reaches 31%@20 mA, which is higher than the previously reported values. Moreover, when coupled with a blue laser diode (LD), the optical output power of the NIR‐cpc‐LD reaches as high as 1652.6 mW@5.5 W. Therefore, GAGG:Cr3+NIR‐cpc‐LD not only shows a great prospect in practical applications, but also provides a new solution for high‐power compact NIR light sources.

Thermally Robust Orange‐Red‐Emitting Color Converters for Laser‐Driven Warm White Light with High Overall Optical Properties

AbstractLaser‐driven solid‐state lighting with super‐brightness and compactness is recognized as a promising alternative to white light‐emitting diodes. However, it is quite difficult to achieve laser‐driven warm white light with long‐term stability due to the shortage of robust orange‐ or red‐emitting laser phosphors. In this work, an efficient and thermally robust orange‐red (La,Y)3Si6N11:Ce3+ (LYSN)‐BN phosphor‐in‐glass (PiG) film is proposed to realize warm white light, where h‐BN acts as an optical medium to enhance light scattering, a heat sink to reduce the temperature, and a protective layer to prevent LYSN from oxidation. The “LYSN+15 wt.% BN” PiG film shows an internal quantum efficiency of 70% and a luminance saturation threshold of 12.82 W mm−2, much higher than those without h‐BN (i.e., 57.5% and 7.63 W mm−2). A warm white light lamp fabricated by combining “LYSN+15 wt.% BN” PiG film with blue laser diodes, showing tunable correlated color temperatures (2800–5000 K), has a maximal luminous flux of 740 lm and a luminous efficacy of 133.5 lm W−1, which promises high collimation and penetration lighting in the rainy or foggy weather. By designing a composite orange‐red‐emitting phosphor converter, this work lays a foundation for realizing high quality laser‐driven warm white lighting source.

Antibacterial Effects of the Novel Blue Laser and Erbium Chromium Laser on Enterococcus Faecalis in Root Canal Dentin with Different Thicknesses.

The aim of this study was to investigate the antibacterial effects of 445 nm blue diode lasers and erbium chromium lasers on the biofilm of Enterococcus faecalis in root canal dentin with different thicknesses. Dentin slices with thicknesses of 300, 500, and 1,000 microns were prepared; and after the biofilm formation, they were randomly divided into four groups: group A : Er, Cr:YSGG laser radiation; group B: 445 nm diode laser radiation; group C : laser radiation in three cycles; and control group D: 5 samples of each thickness were selected as a positive control group. Er, Cr:YSGG and diode lasers alone did not significantly reduce the number of bacteria in any of the thicknesses. Only in 1 mm thick sections, the group exposed with the both Er, Cr:YSGG laser and 445 nm diode laser (66%) significantly reduced the number of bacteria. There was a significant difference in a thickness of 0.3 mm compared to a thickness of 1 mm, indicating that these lasers had a better effect at a thickness of 0.3 mm than at 1 mm parts (P-value < 0.008). It seems that these lasers can be used as an adjunct to conventional chemical methods in cleaning infected canals.

Electrically pumped blue laser diodes with nanoporous bottom cladding.

We demonstrate electrically pumped III-nitride edge-emitting laser diodes (LDs) with nanoporous bottom cladding grown by plasma-assisted molecular beam epitaxy on c-plane (0001) GaN. After the epitaxy of the LD structure, highly doped 350 nm thick GaN:Si cladding layer with Si concentration of 6·1019 cm-3 was electrochemically etched to obtain porosity of 15 ± 3% with pore size of 20 ± 9 nm. The devices with nanoporous bottom cladding are compared to the reference structures. The pulse mode operation was obtained at 448.7 nm with a slope efficiency (SE) of 0.2 W/A while the reference device without etched cladding layer was lasing at 457 nm with SE of 0.56 W/A. The design of the LDs with porous bottom cladding was modelled theoretically. Performed calculations allowed to choose the optimum porosity and thickness of the cladding needed for the desired optical mode confinement and reduced the risk of light leakage to the substrate and to the top-metal contact. This demonstration opens new possibilities for the fabrication of III-nitride LDs.

Highly photo-stable, kHz-repetition-rate, diode pumped circulation-free liquid dye laser with thermal lens management

Liquid dye lasers have long been considered as ideal tunable laser sources in the visible range but are bulky, expensive, and require a complex system for dye circulation. Here, we present a system that relies on a low-cost blue laser diode as the pump source and a sealed dye cell with no flowing circuitry, resulting in a device that combines the convenience and size of a solid-state device with the stability of a liquid organic laser. A very high photo-stability is obtained (up to 1.2 × 109 pulses or 12 days at 1 kHz), which is five orders of magnitude higher than a solid-state dye laser operated in similar conditions. The number of pulses obtainable at low repetition rates is found to be limited by molecular self-diffusion and, hence, related to the total cuvette volume. In contrast, the repetition rate is limited to a few kHz, which suggests that thermal effects play a bigger role than triplet population effects. Thermal effects participate in the suppression of lasing through the buildup of a strong negative thermal lens; correcting the non-aberrant part of this thermal lens by resonator design enables the repetition rate to be pushed up to 14 kHz with possible further optimization. This work shows a route for building off-the-shelf, compact, low-cost, and convenient tunable pulsed lasers in the visible range that have superior stability over organic solid-state lasers.

High power downconversion deep-red emission from Ho3+-doped fiber lasers

Abstract It has been a big challenge in decades for Ho3+-doped fiber laser to produce high emission power in deep-red due to its intrinsic long carrier lifetime in 5I7 energy level. Here, we advance the development of this visible fiber lasers by a novel pumping method that leverages the advantages of blue laser diode downconversion mechanisms to fully pumping, while shortening the lifetime of the lower energy level of the deep-red laser through excited state absorption. For the first time, we demonstrate a downconversion fiber laser using a single wavelength of 532 nm solid-state laser pump source to excite the Ho3+-doped ZBLAN fiber, which achieves a record high maximum output power of 1.64 W at 752.10 nm, as well as free-running of deep-red lasers with watt-level output. This technology represents a milestone in high power deep-red fiber lasers. Importantly, it is readily to be extended to other wavelengths that evidenced its huge application potentials in fiber laser industry.

Improved performance of GaN-based blue laser diodes using asymmetric multiple quantum wells without the first quantum barrier layer.

An asymmetric multiple quantum well (MQW) without the first quantum barrier layer is designed, and its effect on the device performance of GaN-based blue LDs has been studied experimentally and theoretically. It is found that compared with LD using symmetrical multiple quantum well, device performance is improved significantly by using asymmetric MQW, i.e. having a smaller threshold current density, a higher output optical power and a larger slope efficiency. The threshold current density decreases from 1.28 kA/cm2 to 0.86 kA/cm2, meanwhile, the optical power increases from 1.77 W to 2.52 W, and the slope efficiency increases from 1.15 W/A to 1.49 W/A. The electroluminescence characteristics below the threshold current demonstrate that asymmetric MQW is more homogeneous due to the suppressed strain and piezoelectric field. Furthermore, theoretical calculation demonstrates that the enhancement of electron injection ratio and reduction in optical loss are another reason for the improvement of device performance, which is attributed to a smaller electron potential barrier and a more concentrated optical field distribution in the asymmetric structure, respectively. The new structure design with asymmetric MQW is concise for epitaxial growth, and it would also be a good possible choice for GaN-based LDs with other lasing wavelengths.

A diode-pumped femtosecond Pr:YLF laser emitting at the near-infrared 915 nm

Femtosecond pulse generation from diode-pumped praseodymium (Pr) lasers in the near-infrared has been a long pursuit for the optics community. Utilizing the Pr:LiYF4 crystal in a novel dispersion arrangement scheme that includes a set of triple Gires-Tournois interferometer mirrors, mode-locked ultrashort pulses as short as 451 fs at 915 nm have been achieved when the crystal is directly pumped by a blue laser-diode. The pulse energy is 3 nJ and peak power is 7.2 kW at the repetition rate of 85.5 MHz. This is the first demonstration of diode-pumped Pr lasers arriving the femtosecond regime.

Luminous output improvement in chip scale packaged Ce3+:YAG-based ceramic phosphors-converted white LEDs via laser assistance for application in automobile headlights

In this study, two kinds of composite ceramic phosphors, Ce3+:YAG/Al2O3 and Ce3+:Y(Gd)AG/Al2O3 were prepared via solid state reaction sintering in flowing pure oxygen at atmospheric pressure. The ceramic phosphors were packaged into chip-scale white light emitting diodes (w-LEDs), and laser assisted w-LED automobile headlight prototypes were assembled. The luminous flux output of the w-LEDs was significantly improved through additional blue diode laser excitation. Notably, the Al2O3 phase is able to impart an improvement in the luminescence saturation exhibited by Ce3+:Y(Gd)AG, which typically reaches saturation prior to Ce3+:YAG.

Leveraging 3-D Printer With 2.8-W Blue Laser Diode to Form Laser-Induced Graphene for Microfluidic Fuel Cell and Electrochemical Sensor

Realization of laser-induced graphene (LIG) by ablating laser on several substrates, like polyamide (PI), has gained huge attention. Generally, a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser, with a 10.6- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> wavelength, has been reported to form LIG. However, higher build area, the requirement of a higher power, limited LIG conductivity values, infrared wavelength, and cost are several drawbacks of the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser-based process. Herein, a 3-D printer, loaded with a low-power (2.8 W) blue (450 nm) laser diode, has been demonstrated to create such LIGs with higher conductivity on PI sheets. The LIGs, with varying conductivity values, have been fabricated by diversified laser parameters achieving maximum conductivity of 2572.19 S/m, which was more than seven times higher than the one achieved by a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser. Subsequently, such LIG was transferred to a lamination sheet, named T-LIG, using a laminator. Finally, T-LIG based microfluidic device was developed with a microchannel and three integrated electrodes for electrochemical detection of folic acid, achieving a limit of detection of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10 ~\mu \text{M}$ </tex-math></inline-formula> . Similarly, a microfluidic fuel cell was developed using T-LIG which provided a maximum power density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.06 ~\mu \text{W}$ </tex-math></inline-formula> / cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with a maximum open-circuit voltage of 50 mV. Overall, such T-LIG-based microfluidic devices have huge potential for diverse applications.

Demonstration of a simple approach for sub‐microliter fluorescence detection by structured PDMS cuvette with TiO 2 nanoparticle inclusion using 3D printing technology

With the increasing importance of portable sensing devices, one keeps seeking possible optimization to detect the lower concentration of target molecules with reduced reagents. Here presents a method to enhance fluorescence detection through a miniature cylindrical lens integrated into an engineered PDMS cuvette with a high refractive index embedded TiO2 nanoparticles. 3D printing technique was used to develop the moulds where the custom cuvette is produced utilizing the imprinting method. LED transmitter and blue laser diode were used as the excitation light sources to verify the light and materials interactions. In all the experiments, the fluorescence detection system was set at 90° alignments without any filters. First, the square-shaped cuvette resulted in more fluorescence detection compared to the circular one. Hence, different fluorophore holders with square shapes were designed to investigate the efficiency of the integrated lens and the TiO2 nanoparticles inclusions. Overall, the customized cuvette with integrated lens and nanoparticles demonstrated the most significant signal enhancement that reached the lower detection limit as 10 nM/L in 1 μL detection volume. This structural and material-modified cuvette can significantly enhance fluorescent detection at a sub-microliter scale, allowing further device miniaturization, especially for micro and nano fluidic devices using optical detection.

Spectroscopic characteristics of Dy3+-doped Ca2Al2SiO7 single crystal for potential use in solid-state yellow lasers

In this paper, a Dy3+:Ca2Al2SiO7 single crystal was grown successfully by the Czochralski technique. The effective segregation coefficient of Dy3+ ions in Dy3+:Ca2Al2SiO7 crystal was measured to be 1.12. The crystal's spectroscopic properties were investigated in detail. The absorption cross sections at 452 nm are 1.03 × 10−21 cm2, and 0.98 × 10−21 cm2 with the full width at half maximum 10.79 and 4.89 nm for π- and σ-polarizations, respectively. Based on the Judd-Ofelt theory, the radiative transition probabilities, fluorescence branching ratios, and radiative lifetime of Dy3+:Ca2Al2SiO7 crystal were obtained. The emission cross sections at 574 nm are 13.82 × 10−21 cm2, and 8.33 × 10−21 cm2 for π- and σ-polarizations, respectively. The fluorescence decay time of 4F9/2 multiplet is 334.9 μs, and the fluorescence quantum efficiency is 58.6%. These results show that Dy3+:Ca2Al2SiO7 crystal is a promising yellow laser material suitable for commercial 450 nm blue laser diode pumping.