High-power Laser Illumination Research Articles

Heat dissipation enhancement of PiGF converter with vapor chamber radiator for high-brightness laser lighting

Laser illumination is widely believed to have great development potential in high-brightness lighting and display. In order to realize high-power laser illumination, an efficient heat dissipation method was proposed for phosphor-in-glass film (PiGF) color converter. The heat dissipation of PiGF converter was enhanced by the vapor chamber radiator (VC). The VC-PiGF converter demonstrates great optical-thermal performances due to its excellent heat dissipation capability. The maximum luminous flux of VC-PiGF converter (3699.3 lm) is 38.2 % higher than that of traditional fin-PiGF converter (2677.1 lm). The VC-PiGF converter has higher laser power saturation threshold (maximum 34.51 W) than the fin-PiGF converter (maximum 29.12 W). As the laser power is 24.82 W, the operating temperature of VC-PiGF converter (128 °C) is 41.8 % lower than that of fin-PiGF (220 °C). In addition, the VC-PiGF converter exhibits stable optical performances and a low surface temperature with the continuous excitation of 15.78 W for 60 min. The VC-PiGF converter packaged in a lighting module has an excellent outdoor test result. The efficient heat dissipation method with high reliability has great application prospects in high-brightness laser lighting.

Highly heat-dissipating phosphor-in-glass film converter for high‐luminance laser lighting

A new phosphor-in-glass film (PiGF) color converter with high heat dissipation capability was proposed for high-power laser illumination. To intensify heat conduction, a composite structure was fabricated by welding the PiGF to a copper block through a silver layer. The PiGF converter was found to have a high quantum yield and similar fluorescence lifetime as the original phosphors. The optical characteristics of this material were investigated by varying the thickness of PiGF and the lase power. Under the excitation of 8.78W laser power, the PiGF converter with 100 μm film thickness enables a luminous efficacy of 187.9 lm/W, a CCT of 6150 K, and a perfect chromaticity coordinate of (0.3174, 0.3351). In addition, a maximum luminous flux of 4449 lm was obtained when the laser power reached 27.42 W. Besides, The PiGF converter displayed low working temperature and stable optical performance under the sustained excitation test, which indicates that the PiGF converter exhibits excellent opto-thermal performances. In general, an effective solution is put forward for the heat dissipating obstacle of laser lighting.

Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications

We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications.

β-Sialon:Eu2+ phosphor-in-glass: An efficient and potential green color conversion material for laser lighting systems

With the high demand of modern people for lighting quality, higher requirements have been put forward for the lighting technology. Compared with traditional light emitting diodes (LEDs), laser diode (LD)-driven lighting technology has more prominent advantages in the fields of industry, military and life. Here, we report a phosphor-in-glass (PiG) material formed by co-firing commercial β-Sialon:Eu2+ phosphor and SiO2-Na2CO3-H3BO3-CaO (SNBC) glass. It is found that the powder perfectly dispersed in the glass without obvious interface reaction. Fluorescence intensity of PiG sintered at 800 °C is the strongest, and the position of the luminescence peak is around 540 nm. Then through the analysis of different concentrations of PiG phosphors, it is found that the internal quantum efficiency (IQE) can reach 72%. The specific heat capacity decreases with the increase of temperature, indicating that the heat dissipation effect is fine. Under the blue LD irradiation of 450 nm, the luminous flux of the PiG sample reaches 363 lm and the high luminous efficiency of 154 lm/W. Our research found that the prepared β-Sialon-PiG can provide green light for high-power laser illumination and is a stable and efficient fluorescent conversion material.

Plasmon-Enhanced Electron Harvesting in Robust Titanium Nitride Nanostructures

Titanium nitride (TiN) continues to prove itself as an inexpensive, robust, and efficient alternative to gold in plasmonic applications. Notably, TiN has improved hot electron-harvesting and photocatalytic abilities compared to gold systems, which we recently attributed to the role of oxygen in TiN and its native semiconducting TiO2–x surface layer. Here, we explore the role of localized surface plasmon resonances (LSPRs) on electron harvesting across the TiN/TiO2–x interface and probe the resilience of TiN nanostructures under high-power laser illumination. To investigate this, we fabricate TiN strips, in which the lateral confinement allows for the polarization-selective excitation of the LSPR. Using ultrafast pump–probe spectroscopy, optical characterization, and Raman vibrational spectroscopy, we relate the differences and changes observed in the electron behavior to specific material properties. We observe plasmon-enhanced electron harvesting beyond what is expected resulting from the enhanced absorp...

Speckle reduction in laser projection using a dynamic deformable mirror.

Despite of much effort and significant progress in recent years, speckle removal is still a challenge for laser projection technology. In this paper, speckle reduction by dynamic deformable mirror was investigated. Time varying independent speckle patterns were generated due to the angle diversity introduced by the dynamic mirror, and these speckle patterns were averaged out by the camera or human eyes, thus reducing speckle contrast in the final image. The speckle reduction by the wavelength diversity of the lasers was also studied. Both broadband lasers and narrowband laser were used for experiment. It is experimentally shown that speckle suppression can be attained by the widening of the spectrum of the lasers. Lower speckle contrast reduction was attained by the wavelength diversity for narrowband laser compared to the broadband lasers. This method of speckle reduction is suitable in laser projectors for wide screen applications where high power laser illumination is needed.

The UV-laser induced heating effect on photoluminescence from ZnO nanocrystals deposited on different substrates

Photoluminescence (PL) from ZnO nanocrystals deposited on silicon, sapphire and glass substrates was measured at different temperatures and UV-laser excitation densities. Our studies show that the PL properties of the nanocrystals are a strong function of the ultraviolet laser excitation density and the thermophysical properties of the substrates used. Even at low temperatures (10–30 K), high-power laser illumination can heat the top layer of nanocrystals up to 100 K. The heating effect induced by laser illumination results in a saturation behaviour of the PL intensity with increasing excitation density. It is determined that the degree of the saturation depends on the substrates' thermophysical properties.

Annealing effects on single Shockley faults in 4H-SiC

We investigated the annealing effect on single Shockley faults (SSFs) in the SiC epitaxial layers by photoluminescence mapping in combination with high-power laser illumination. Comparing before and after annealing at 350–550°C, it became obvious that annealing results in the shrinking of the faulted area of SSFs. When high-power laser illumination is performed again on the same area annealed at 550°C, the right-angled triangular SSFs reformed into exactly the same features as those before annealing, but the isosceles triangular SSFs did not reform. The annealing temperature to start shrinking the faulted area differs according to the type of SSF.

Thermal analysis of micromirrors for high-energy applications

This paper presents the results of an investigation of the thermal mechanism between lasers and surface-micromachined micromirrors. Finite element models using ABAQUS are established and used to study the temperature distribution on the surface of micromirrors under high-power laser illumination. It is shown that heat conduction through the gas gap between the mirror surface and the substrate is the dominant thermal dissipation mechanism for high surrounding gas pressure, while heat conduction through the flexures is dominant for low surrounding gas pressure. Based on the simulation results, two novel methods are proposed in order to tolerate more power input under low surrounding gas pressure. The results of optical power testing validate these models, and indicate that these two approaches are efficient in improving micromirror performance for high-energy applications.

All-reflective Michelson, Sagnac, and Fabry–Perot interferometers based on grating beam splitters

All-reflective Michelson, Sagnac, and Fabry-Perot interferometers based on grating beam splitters are experimentally demonstrated at a wavelength of 1064 nm. A 1200-groove/mm grating diffracting 0 and -1 orders with an efficiency of 48.2% for each order was used as a near-50/50 beam splitter. The all-reflective Sagnac and Michelson interferometers were formed by reintroducing both of the diffracted beams back to the grating. The Fabry-Perot interferometer was formed in a Littrow configuration by using a 1700-groove/mm grating with a blazing efficiency of 91% as a cavity coupler. These interferometers encompass all the fundamental configurations of all-reflective laser interferometric gravitational-wave detectors, promising improved wave-front quality by avoiding volume thermal effects in transmissive optics under high-power laser illumination.

Efficient optical enhancement of acousto-optic diffraction using optimized overlap of coupled waves

We describe a technique by which the diffraction efficiency of an acousto-optic beam deflector may be substantially increased under high-power laser illumination. In earlier research we showed that the diffraction process is intrinsically associated with an intensity-dependent modification of the diffraction efficiency of an acousto-optic device. Here we show that this diffraction efficiency may be enhanced most effectively by distributing the optical intensity over the acousto-optic device in a manner that maximizes the overlap with the acoustic wave in the medium. In particular, we demonstrate increases in diffraction efficiency of greater than 80% in a TeO(2) device-an improvement of roughly an order of magnitude over earlier results in which this overlap technique was not used.

Anomalous behaviour in the saturation of the sodium D lines under high power laser illumination

The authors have confirmed earlier observations that fluorescence from dense sodium vapour under high power illumination does not saturate with increasing laser intensity. Direct observations of level population using a variant of the interferometric hook technique with a time resolution of ten nanoseconds have been performed, showing that the level populations of the pumped transition were in the ratio of their statistical weights. The apparent contradiction between this result and that of the laser-induced fluorescence observations is considered.

Anomalous fluorescence scattering from shock-heated sodium vapour under maintained high-power laser illumination

A fluorescence measurement on sodium in a neon atmosphere is reported. The expected saturation of the emission at right angles could not be detected even at very high laser powers. Possible explanations are considered.