High-power Laser Light Research Articles

Tailoring thermal behavior and luminous performance in LuAG:Ce films via thickness control for high-power laser lighting applications

Tailoring thermal behavior and luminous performance in LuAG:Ce films via thickness control for high-power laser lighting applications

Optical properties of Ce: GdYAG phosphor in glass with high quality LAS glass system and its application in laser illumination

Nowdays, the demand for high-power laser lighting applications is on the rise, however, phosphor in glass (PiG) prepared using conventional glass systems often experience damage under intense laser irradiation. To tackle this issue, we introduce a novel LAS glass system for phosphor encapsulation to create PiG, and by utilizing a spray coating technique, we blend PiG with high thermal conductivity sapphire to obtain phosphor in glass film (PiF), effectively improving laser irradiation resilience and optical characteristics. In this study, a novel LAS glass system (SiO2–Li2CO3–MgO–Al2O3–CaO–P2O5–K2O–ZrO2–Na2O) was utilized to encapsulate Ce:GdYAG phosphors to prepare a series of PiG and PiF. The glass system exhibits multi-directional interlocking lithium disilicate crystals, significantly enhancing the glass's strength and fracture toughness. There is no apparent interface reaction between the glass system and the phosphors, indicating effective protection of the phosphor particles. The PiF sample demonstrates a minor decrease of 5.2 % in internal quantum efficiency compared to the original phosphor, while boasting a high thermal conductivity of 7.4 W m−1 K−1. Notably, the optimized PiF shows remarkable enhancements with a saturation threshold of 4.37 W mm−2, surpassing PiG (1.668 W mm−2), and achieving LFmax of 424.41 lm and LEmax of 147.16 lm W−1. It features a high color rendering index (CRI) of 68.7 and low color correlated temperature (CCT) of 3646 K, significantly improving laser irradiation resistance and optical quality, making it a promising warm yellow laser illumination converter for diverse lighting applications.

High luminous efficiency and excellent thermal performance in rod-shaped YAG:Ce phosphor ceramics for laser lighting.

High power and high brightness laser lighting puts forward new requirements for phosphor converters such as high luminous efficiency, high thermal conductivity and high saturation threshold due to the severe thermal effect. The structure design of phosphor converters is proposed as what we believe to be a novel strategy for less heat production and more heat conduction. In this work, the rod-shaped YAG:Ce phosphor ceramics (PCs) and disc-shaped YAG:Ce PCs as control group were fabricated by the gel casting and vacuum sintering, to comparatively study the luminescence performance for LD lighting, on the premise that the total number of transverse Ce3+ ions and the volume of samples from two comparison groups were same. All rod YAG:Ce PCs with low Ce3+ concentration exhibited the high luminous efficiency and better thermal stability than YAG:Ce discs with high Ce3+ concentration. Under the laser power density of 47.8 W/mm2, the luminous saturation was never observed in all rod-shaped YAG:Ce PCs. The high luminous efficacy of 245∼274 lm/W, CRI of 56.3∼59.5 and CCT of 4509∼4478 K were achieved. More importantly, due to the extremely low Ce3+ doping concentration (0.01 at%), rod-shaped ceramics based LDs devices showed the excellent thermal performance and their surface temperatures were even below 30.5 °C surprisingly under the laser power density of 20.3 W·mm-2 (2 W). These results indicate that the rod shape of phosphor converter is a promising structure engineering for high power laser lighting.

High efficiency and stable La3Si6N11:Ce phosphor-in-glass film for high power laser lighting

As an inorganic color conversion material, phosphor-in-glass film (PiF) has received extensive attention in the sphere of laser-driven white lighting due to its excellent integrated performance. The yellow-emitting phosphor La3Si6N11:Ce has excellent thermal stability and wide emission band, which makes it more competitive than Y3Al5O12:Ce in laser-driven white lighting. Herein, we embedded La3Si6N11:Ce phosphor powder in a silicate glass matrix (SiO2–B2O3–CaO–Na2O) and sintered it on a sapphire substrate. In the silica-rich glass system, the network structure of silica-oxygen tetrahedral glass is more rigid and the thermal erosion of the phosphor by the silica-based glass is less, which makes the phosphor maintain better performance after low-temperature co-sintering. The quantum efficiency in the optimized LSN phosphor-in-glass film (LSN PiF) is up to 81 %, and the thermal conductivity is 10.2 Wm−1K−1, showing good thermal stability. Impressively, the LSN PiF produces a bright near-white light (0.3323,0.346) at a blue laser of 5.6 W, with corresponding luminous efficiency up to 195 lm/W. Moreover, LSN PiF can maintain about 80 % of the initial luminous intensity after continuous lighting for 24 h at the incident power of 3.5 W. These outstanding properties can advance the development of LSN phosphors in high power laser lighting applications.

Low-loss multi-mode anti-resonant hollow-core fibers.

In this work, multi-mode anti-resonant hollow-core fiber (AR-HCF) with 18 fan-shaped resonators is fabricated and characterized. The ratio of core diameter over transmitted wavelengths in the lowest transmission band is up to 85. The measured attenuation at 1 µm wavelength is below 0.1 dB/m and the bend loss below 0.2 dB/m at a bend radius smaller than 8 cm. Modal content of the multi-mode AR-HCF is characterized using the S2 imaging technique and seven LP-like modes in total are identified using a 23.6 meter fiber length. Multi-mode AR-HCFs for longer wavelengths are fabricated by scaling up the same design, extending the transmission window beyond 4 µm wavelength. Low-loss multi-mode AR-HCF could find applications in the delivery of high-power laser light with a medium beam quality, where higher coupling efficiency and laser damage threshold are expected.

A multifunctional nanoplatform based on Fe3O4@Au NCs with magnetic targeting ability for single NIR light-triggered PTT/PDT synergistic therapy of cancer

Although simultaneous photothermal therapy (PTT) and photodynamic therapy (PDT) have been proven to be beneficial for cancer treatment, high-power laser light sources, shallow penetration depth of light and especially activation by two different light sources make it difficult to be popularized in clinical cancer therapy. Herein, the novel multifunctional Fe3O4@Au nanocomposites (NCs) have been designed and synthesized, which simultaneously act as photothermal conversion agents (PCAs) and photosensitizers (PSs) for PTT/PDT synergistic therapy of human cervical cancer (HeLa) cells using a single excitation light source. Under low-power 808 nm laser irradiation, photothermal conversion efficiency (PCE) of Fe3O4@Au NCs was as high as 39.22% and the cytotoxic singlet oxygen (1O2) could be simultaneously generated. In addition, Fe3O4@Au NCs showed relatively good biocompatibility and low cytotoxicity, which were ideal alternatives for nanotherapeutic agents for treatment of HeLa cells. Meanwhile, PTT only and PTT/PDT dual-modal therapeutic effects of Fe3O4@Au NCs on HeLa cells were compared. The experimental results confirmed that the near-infrared (NIR)-triggered PDT/PTT synergistic therapy of HeLa cells was more efficient due to the synergistic effect. Interestingly, Fe3O4@Au NCs with saturation magnetization (Ms) value of 66.5 emu/g possessed good magnetic responsivity, which could be collected easily with a magnet. The magnetic targeting of Fe3O4@Au NCs could effectively promote their accumulation at tumor sites, thus further enhancing the efficacy of PTT/PDT synergistic therapy of HeLa cells. This study provides a feasible paradigm for magnetic targeting-assisted PTT/PDT synergistic therapy of cancer cells under a single-wavelength excitation and opens up a novel direction for clinical cancer therapy.

Significant enhancement of luminescence properties of YAG:Ce ceramics by differential grain sizes control

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al2O3–YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al2O3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting.

Ultra-high efficiency green-emitting LuAG: Ce phosphor-in-ceramic applied for high-power laser lighting

Phosphor-in-ceramic (PiC) has garnered considerable attention in high-power white laser lighting owing to its advantages, such as high efficiency and good thermal stability. In this study, a transparent hydroxyapatite (HA) ceramic was successfully prepared via spark-plasma sintering (SPS) under relatively mild conditions. A series of ultra-high efficiency green-emitting PiCs were obtained by pure HA ceramics with 1–12% Lu3Al5O12: Ce (LuAG) phosphors. Owing to the rapid sintering of SPS and the stability of HA ceramics, HA ceramic matrix has high transparency, and does not damage the crystal structure of the LuAG phosphor. When excited by a blue laser, the HA-LuAG PiC exhibited an excellent luminous efficacy of 300.48 lm·W−1. The fluorescence saturation threshold of the laser power was approximately 7.90 W. These results demonstrate that HA-LuAG PiCs have great potential for applications as efficient green-emitting phosphor conversion materials for high-power laser lighting.

All-inorganic color converter based on a phosphor in bismuthate glass for white laser diode lighting.

Blue laser diodes (LDs) combined with phosphors have been recognized as the next-generation solid white lighting technology. The phosphor-in-glass (PiG) coating is used for packaging as an appropriate fluorescent conversion material applied to white light LDs. In this work, a low melting point glass Bi2O3-B2O3-ZnO-BaO (BiBZBa), which was mixed with YAG:Ce3+ phosphor powder, was selected as a glass matrix, and the coating of the phosphor in bismuthate glass (PiBG) was successfully fabricated on different substrates through multilayer screen-printing and low-temperature sintering processes. The PiBG-coated substrates were integrated with a 440 nm LD chip in different interlayer structures to obtain PiBG-packaged white laser diodes (WLDs). The thermal performance of Bi2O3-B2O3-ZnO-BaO glass and the phase composition, microstructure, and luminescence properties of PiBG coatings were studied, and the optical performances of WLDs were investigated. When the reflective WLDs were excited by a blue laser with a laser power density of up to 9.3 W mm-2, the related luminous flux (LF), luminous efficiency (LE), and chromaticity coordinates were 3091 lm, 103 lm W-1, and (0.32, 0.32), respectively, indicating great potential in PiBG-packaged high power laser lighting applications.

Phase composition design of high performance Al2O3-YAG: Ce ceramic phosphors for high-power laser lighting

The combination of laser diode (LD) chip and Al2O3-YAG: Ce composite ceramic phosphor is considered as one of the best solutions for high-power laser lighting. However, in previous studies on Al2O3-YAG: Ce composite ceramics, the effects of large-scale compositional changes on their luminous properties were rarely noticed, which hinders the understanding of the relationship between ceramic phase composition and the comprehensive properties of white LDs. In this paper, we prepared Al2O3-YAG: Ce composite ceramic phosphors with Ce3+ and Al2O3 concentrations varying widely in the range of 0.5–5 at% and 0–90 at%, respectively. An impurity phase was found in samples with high Ce3+-Al2O3 concentration by SEM images and verified to be CeAl11O18 by XRD patterns. Under high power density laser (2.3–10 W/mm2) excitation, the Ce3+ concentrations corresponding to the highest luminous efficiency of the ceramic increase from 0.5 at% to 3 at% with the introduction of Al2O3. The temperature quenching effect of ceramics is also alleviated. The CRI of ceramics first decreases and then increases with the increase of Al2O3 concentration, and the CRI of 90 at% Al2O3 samples is the highest (75.9). The results show that the introduction of Al2O3 can improve the performance of ceramics from all aspects as long as the optimal composition of Al2O3- YAG: Ce composite ceramics is selected.

Design of a Novel La3Si6N11:Ce3+ Phosphor-in-Glass Film for High Power Laser Lighting: Luminous Efficiency toward 200 lmW–1

Inorganic fluorescent glass films have been widely considered in the field of high power laser lighting because of their excellent comprehensive properties as fluorescent conversion materials. Herein, we adjust the optimum sintering temperature to prepare a series of La3Si6N11:Ce3+ phosphor-in-glass films (LSN PiFs) with excellent optical properties on a single sapphire structure. The prepared LSN PiF has ultrahigh internal quantum efficiency (IQE) (98%) and excellent thermal stability. The thermal conductivity at room temperature can reach 9.8 Wm–1 K–1. When the temperature is 100 °C, the fluorescence intensity can still be maintained. The LSN:Ce phosphor particles did not react with the glass matrix and retained the original luminescence properties. Moreover, by further adjusting the concentration and thickness of LSN PiF, the luminous flux and luminous efficiency of LSN PiF under optimal conditions can reach 1071.73 and 207.58 lmW–1 under the excitation of 460 nm, which is the optimal result reported so far. In addition, the color rendering index (CRI) and low color temperature (CCT) are 64.05 and 5612.6 K, respectively, and the color coordinates are all close to the white light region. All the results show that LSN PiF has great application prospects in the high quality and high brightness laser lighting field.

A temporal-spatio detection model and contrast calculation method on new active sky screen with high-power laser

To improve the detection performance of sky screen under different background environments, this paper invents an active sky screen by using high-power laser light source to form active detection screen, which makes use of the advantages of the sky screen detection receiving light path and photoelectric detection sensor made of new materials. Based on the design method of active sky screen, the temporal-spatio detection model of active sky screen is established by combining the distribution characteristics of laser light sources in any position and detection screen parameters; the surface of projectile is decomposed into a multiple small units area, and the calculation function of projectile’s reflected laser power is deduced by using the superposition principle of the reflected laser energy of multiple small units area and four parameter BRDF. According to the features of blue sky and cloudy background, the different of the projectile’s reflected laser energy and the shading image energy of projectile itself is used to evaluate contrast and derive the new contrast calculation function of active sky screen. Through experimental testing and quantitative calculation analysis, the proposed computational model and contrast function are validated.

Kilowatt-average-power single-mode laser light transmission over kilometre-scale hollow-core fibre

High-power laser delivery with near-diffraction-limited beam quality is typically limited to tens of metres distances by nonlinearity-induced spectral broadening inside the glass core of delivery fibres. Anti-resonant hollow-core fibres offer not only orders-of-magnitude lower nonlinearity but also loss and modal purity comparable to conventional beam-delivery fibres. Using a single-mode hollow-core nested anti-resonant nodeless fibre with 0.74 dB km−1 loss, we demonstrate the delivery of 1 kW of near-diffraction-limited continuous-wave laser light over a 1 km distance, with a total throughput efficiency of ~80%. From simulations, a further improvement in transmitted power or length of more than one order of magnitude should be possible in such air-filled fibres, and considerably more if the core is evacuated. This paves the way to multi-kilometre, kilowatt-scale power delivery that is potentially useful not only for future manufacturing and subsurface drilling but also for new scientific possibilities in sensing, particle acceleration and gravitational wave detection. Microstructured optical fibre is shown to be able transmit high-power laser light over long distances with high throughput efficiency.

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.

Diamond mirrors for high-power continuous-wave lasers

High-power continuous-wave (CW) lasers are used in a variety of areas including industry, medicine, communications, and defense. Yet, conventional optics, which are based on multi-layer coatings, are damaged when illuminated by high-power CW laser light, primarily due to thermal loading. This hampers the effectiveness, restricts the scope and utility, and raises the cost and complexity of high-power CW laser applications. Here we demonstrate monolithic and highly reflective mirrors that operate under high-power CW laser irradiation without damage. In contrast to conventional mirrors, ours are realized by etching nanostructures into the surface of single-crystal diamond, a material with exceptional optical and thermal properties. We measure reflectivities of greater than 98% and demonstrate damage-free operation using 10 kW of CW laser light at 1070 nm, focused to a spot of 750 μm diameter. In contrast, we observe damage to a conventional dielectric mirror when illuminated by the same beam. Our results initiate a new category of optics that operate under extreme conditions, which has potential to improve or create new applications of high-power lasers.

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.

Thermal and optical investigations of self-loop system based on liquid quantum dots for laser lighting

This study proposes a self-loop converter (SLC) based on liquid quantum dots (QDs) that is designed for laser lighting. QDs exhibit unique illumination and display advantages because of their high light conversion efficiency and color purity. However, the unavoidable heat generated during light conversion leads to thermal quenching and limits their application in high-power laser lighting. The proposed SLC reduces the temperature and temperature fluctuations in the excited heating and gas circulation areas. After excited by laser for 240 min, the radiation power only decreases from 529.65 mW to 464.13 mW, a decrease of 12.37%. But the radiation power of hermitic converter (HC) decreased from 520.52 mW to 361.35 mW, decreasing by 30.5% after excited by laser for the same time. The experimental results demonstrate that the proposed SLC is promising for laser headlights, aerospace, coal mining, and other fields.

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.

Effect of Rosensweig instability in a ferrofluid layer on reflection loss of a high-frequency electromagnetic wave

A ferrofluid layer separates into numerous subscale crests, which is referred to as Rosensweig instability, whose shape and size depend on the field condition and the composition of the ferrofluid. A ferrofluid consisting of nanoscale magnetite particles is also used as an electromagnetic (EM) wave absorption and reflection material. For this study, oil-based and mixture ferrofluid layers that split into various shapes of crests in the presence of an external magnetic field are used to form a protruding structure to reflect and scatter the EM wave and decrease EM radiation energy. For an identical field strength, a mixture ferrofluid layer splits into more crests than an oil-based ferrofluid. A mixture crest shows a less uniform size and shape than the oil-based one. A high-power green laser light is used as a visual EM wave emitting to a crest, which has varying tip angles, and to demonstrate the reflection and scattering. The reflection loss increases as the field strength is increased to create a crest of a smaller tip angle. The reflection loss of an EM wave is significantly affected by the transmitting position on a crest and the shape of a crest. Inter-reflection arises if an EM wave is repeatedly reflected on the surfaces of crests, which contributes to a significant reflection loss. An EM wave incident at an angle of 45° on a crest resulting in a larger area of the inter-reflection zone without specular reflection in a trough gives the most significant reflection loss.

Fundamental Concepts and Discussion of Plasma Physics

Plasma physics is the state of matter, which consists of charged particles. Plasma is usually produced by heating a gas so that the electrons are separated from the atom or molecule from which it is made. Upper ionization can be performed using high power laser or microwave lighting. Plasma occurs naturally in stars and space. In physics, a plasma is an electrical conductor that has the same number of positively and negatively charged particles. What happens when atoms of a gas are ionized. It is sometimes called the fourth state of matter. Unlike rigid bodies, liquids and gases, negative ions are often carried by electrons. Every work has a reverse side. Positive charges are usually carried by atoms or molecules that do not have identical electrons. In some rare but curious cases, the missing electrons of one type of atom or molecule bond with another. As a result, positive and negative ions are present in the plasma. The most severe cases of this type occur when the dust is low. But as dust particles, they are added in a state known as plasma dust. The peculiarity of the state of the plasma is due to the value of the electrical and magnetic energy acting on the plasma. Affects all types of matter, except for gravitational attraction. Because the electromagnetic force can work over long distances. Therefore, the plasma acts as a fluid group. Although the particles rarely collide. Almost all visible objects in the Universe are in the plasma state. Most of them are found in sunlight and stars in this form. And the space between planets and stars, auroras, lightning and arcades are also plasma. Available with both plasma and fluorescent lamps. In addition to the rigid crystalline structure of the metal, among many other phenomena and objects, the Earth itself is immersed in a thin plasma. Called the solar wind and surrounded by a dense plasma called the ionosphere.