Improve Illumination Uniformity Research Articles

Ameliorating Uniformity and Color Conversion Efficiency in Quantum Dot-Based Micro-LED Displays through Blue-UV Hybrid Structures.

Quantum dot (QD)-based RGB micro light-emitting diode (μ-LED) technology shows immense potential for achieving full-color displays. In this study, we propose a novel structural design that combines blue and quantum well (QW)-intermixing ultraviolet (UV)-hybrid μ-LEDs to achieve high color-conversion efficiency (CCE). For the first time, the impact of various combinations of QD and TiO2 concentrations, as well as thickness variations on photoluminescence efficiency (PLQY), has been systematically examined through simulation. High-efficiency color-conversion layer (CCL) have been successfully fabricated as a result of these simulations, leading to significant savings in time and material costs. By incorporating scattering particles of TiO2 in the CCL, we successfully scatter light and disperse QDs, effectively reducing self-aggregation and greatly improving illumination uniformity. Additionally, this design significantly enhances light absorption within the QD films. To enhance device reliability, we introduce a passivation protection layer using low-temperature atomic layer deposition (ALD) technology on the CCL surface. Moreover, we achieve impressive CCE values of 96.25% and 92.91% for the red and green CCLs, respectively, by integrating a modified distributed Bragg reflector (DBR) to suppress light leakage. Our hybrid structure design, in combination with an optical simulation system, not only facilitates rapid acquisition of optimal parameters for highly uniform and efficient color conversion in μ-LED displays but also expands the color gamut to achieve 128.2% in the National Television Standards Committee (NTSC) space and 95.8% in the Rec. 2020 standard. In essence, this research outlines a promising avenue towards the development of bespoke, high-performance μ-LED displays.

Active illumination uniformity with narrow spectrum laser based on ladderlike phase modulation

<sec>Active illumination is a crucial technology for active imaging, active tracking and aiming system. But the atmosphere turbulence distributed over the entire path causes the intensity to fluctuate, which reduces the illumination uniformity seriously. Therefore, it is desirable to find ways to reduce the intensity fluctuation and improve the uniformity of active illumination. It has been revealed that one can improve illumination uniformity by using multi-beam laser illuminator. Another effective approach is partially coherent beam illumination.</sec><sec>In this paper, a novel method is suggested to improve the illumination uniformity. Phase disturbance is induced by a ladder-like phase modulator (LPM) and the transmitting field of narrow spectrum laser is confused, and thus the atmosphere turbulence will be compensated and the illumination uniformity will be improved. The physical models of narrow spectrum laser phase modulation and atmosphere propagation are deduced, and the expression of the facular distribution is obtained. The active-illumination experimental setup with a laser propagation distance of 1.8 km through horizontal atmosphere is established. Based on the facular distribution of illumination laser at 1.8 km, the uniformity and stabilization are achieved. The experimental results indicate that the illumination uniformity and stabilization are both improved. The spatial and central time scintillation indexes are improved from 0.73 to 0.33 and from 0.38 to 0.14, respectively.</sec>

Smoothing scheme for intensity sweep and polarization rotation at a subpicosecond timescale

A novel scheme for decreasing the scattering levels of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), as well as for improving illumination uniformity of focal spots, is proposed. In this scheme, four beamlets in a laser quad are frequency shifted, spatial phase shaped by conjugate phase plates, and counter-rotating circularly polarized by polarization control plates before being focused by wedged lenses. Consequently, the intensity sweep and the polarization rotation of the focal spot in the timescale of a subpicosecond are achieved, resulting in the reduction of the scattering level of SRS and SBS, and also the improvement of the illumination uniformity when the frequency shift among beamlets is comparable to the parametric backscattering growth rate and the filamentation instability growth rate. The theoretical model of the novel smoothing scheme has been established, and the influences of some key parameters including spatial modulation type, peak-to-mean value of phase distortion, and frequency shift have been discussed. Results show that the uniformity of the focal spot of this novel scheme is improved much faster than that of the conventional temporal smoothing scheme, i.e., smoothing by spectral dispersion. The parametric instabilities are significantly reduced and both phase distortion and modulation depth of the laser quad have a large tolerance, opening a new dimension for controlling the incident light in laser plasma interaction.

Combined implementation of smoothing technologies for improving illumination uniformity of laser quad in multi-directions

ABSTRACTAzimuthal smoothing (AS) that enables the focal spot of a laser quad to rotate in a period of a few picoseconds can improve the illumination uniformity. However, the smoothing performance of azimuthal smoothing is worse than that of smoothing by spectral dispersion (SSD) due to the low rotation speed in the center area of the focal spot. A combined implementation of the schemes including smoothing by spectral dispersion, radial smoothing (RS) and azimuthal smoothing is discussed to achieve better and faster illumination uniformity. The theoretical models of the combined smoothing scheme have been built up to analyse the smoothing performance. The key parameters affecting the smoothing performance of the combined smoothing scheme are analysed and optimized, including the topological charge and the wavelength difference. The simulation results show that the illumination uniformity of the laser quad can be significantly improved in multi-directions by the combined smoothing scheme.

Optimization of radial smoothing scheme for improving illumination uniformity of laser quad

Radial smoothing scheme based on the optical Kerr effect can add periodical spherical wavefront modulation to the laser beam and make the speckles within the focal spot in far field sweep periodically in radial direction, which improves the illumination uniformity of the laser beam on target in inertial confinement fusion facilities. In order to analyze the smoothing performance of radial smoothing scheme in a laser quad, the corresponding theoretical model was established and the temporal characteristic parameters of the pump laser were further analyzed and optimized. The results show that the fluctuation of the smoothing performance with time can slow down by appropriately adjusting the delay time between the laser beam and pump laser pulses in a laser quad. Furthermore, the different sweep period of the incoherent beams can be obtained by altering the pulse duration of pump laser pulses in a laser quad. Consequently, the group velocity of intensity envelope becomes faster with the increase of the frequency difference between incoherent beams. What’ more, a better smoothing performance can be achieved by applying the appropriate spatial deflection between the laser beam and pump laser pulses in a laser quad, and the deflection angle of the pump laser in a laser quad was further optimized to improve the illumination uniformity on target significantly. Radial smoothing with obliquely incident pump laser can add a spherical wavefront to the laser beam, and further makes the speckles redistribute rapidly both in radial and transverse directions. With appropriate incident direction and angle, RS can achieve a much better final smoothing performance than 2D-SSD.

Optical design of dental light using a remote phosphor light-emitting diode package for improving illumination uniformity

The projection-type dental lighting based on the remote phosphor light-emitting diode (LED) package is designed to enhance uniformity of illuminance and correlated color temperature (CCT) on a target plane and to remove glare in the eyes of the patient. This dental lighting enables dentists to illuminate effectively the patient's mouth by increasing the inner area (50 mm×25 mm) described in ISO 9680. The optical module comprised of the LED package and optical lens is modeled to satisfy the inner area wider than 100 mm×50 mm and illuminance over 5,000lx per the designed optical module. The fabricated prototype dental lighting contains four optical modules, and the maximum illuminance is 22,786lx. The measured inner area is 105 mm×74 mm, and the ratio of inner area to outer area is about 76%. Also, the CCT variation is below 450K in total illuminance pattern.

Illumination uniformity improvement in digital micromirror device based scanning photolithography system.

Illumination uniformity in photolithography systems determines the dimensional difference across the entire lithographic substrate. However, traditional lithography system relies on expensive and complex illumination system for achieving uniform illumination. In this paper, we propose a simple and cost-effective method based on the modulation of digital micromirror device to improve illumination uniformity. The modulation according to a digital mask achieved via an iteration program improves the uniformity to be above 95%. We demonstrate the effectiveness of the method by experimentally fabricating a linear grating. By implementing this method, the maximum dimensional difference is decreased from 3.3μm to 0.3μm. Further simulations indicate that higher uniformity is achievable once the field of view on the DMD is divided into smaller subregions.

A novel radial beam smoothing scheme based on optical Kerr effect

Laser-beam illumination uniformity is a key issue in inertial confinement fusion facilities. In order to fulfill the requirement of improving illumination uniformity, a radial smoothing (RS) scheme is proposed. For smoothing the focal-spot pattern on a short time scale compared with the hydrodynamic response time of the target, the optical Kerr effect with extremely response time is taken into consideration. The basic principle of RS based on optical Kerr effect is that by using the interaction between optical Kerr medium and periodic Gaussian pulses to modulate a periodic spherical phase, to modulate periodic sphericel phase added at the wavefront of laser transmission wave, change the focal-spot size of the laser beam in far field, and further induce the fast radial redistribution of the speckles inside the focal spot in far field, and further induce the fast radial redistribution of the speckles inside the focal spot in far field. This fast radial redistribution of the speckles smoothes the intensity modulation of the focal spot on the target and eventually achieves the beam smoothing in the radial direction. The application of RS in the beamline is detailed. The optical Kerr medium is inserted in the front-end of the bemline, before the laser beam is injected into the main amplifier. The periodic Gaussian pulse for pumping the optical Kerr medium is obtained by the pulse stacking system based on fibers. The pulse width of stacked Gaussian pulse and the time delay between Gaussian pulses are set to be on a picosecond time scale or subpicosecond time scale. The induced refractive index of the optical Kerr medium by the pump laser fits spherical distribution with periodic variation, and results in the radial distribution of the speckles in focal plane. By establishing the theoretical model of the radial beam smoothing scheme implemented with continuous phase plate (CPP), the focusing characteristics of laser beam with RS and CPP are discussed in detail. The influences of the selection of optical Kerr medium and the characteristics of the radial redistribution on the radial smoothing effect are simulated and analyzed. Results indicate that the RS based on optical Kerr effect could efficiently achieve the periodic radial redistribution of the speckles on focal plane, and therefore improves the illumination uniformity in the radial direction while eliminating the stripe pattern presented in far field by one-dimensional smoothing spectral dispersion (SSD). The smoothing performance of RS is different from that of the conventional SSD due to its radial smoothing direction. Moreover, the combined application of RS with continuous phase plate could achieve a better smoothing level with a shorter time. The utilization of radial smoothing scheme in high power laser system may significantly improve the laser-beam irradiation with little influence on the performance of the beamline.

Tailoring freeform illumination optics in a double-pole coordinate system

We have developed a new method to design freeform illumination optics by introducing a double-pole coordinate system in ray mapping. This method establishes a much more accurate ray mapping by moving the two poles of the spherical coordinate system to the southernmost point of the sphere and overlapping them together. It can reduce surface error and improve illumination uniformity significantly. The residual surface error (RSE) of the freeform lens designed in the double-pole coordinate system is one magnitude smaller than that of the lens designed in the (θ,φ) coordinate system and is only 1/3 of that of the freeform surface designed in the (u,v) coordinate system.

Illumination Uniformity Measurement Technology Research Based on Quasi-Sine Particle Swarm Optimization

Illumination uniformity measurement technology of target is a main factor that influences the instruments’ function assessing and ballistic test. Non-linear optimizing strategy of illumination uniformity is introduced in this paper, and the method is put forward to improve illumination uniformity based on Quasi-sine Particle Swarm Optimization. This paper describes the basic principle and implementation steps of the algorithm. The objective function and the degree of orientation function are given. The objective function of optimization results show that the algorithm is convergent and the overall lighting objectives of the symmetry are obtained.

Illumination Uniformity Research Based on Quasi-Sine Particle Swarm Optimization

This text aims at non-linear optimizing problem of illumination uniformity, and puts forward the method to improve illumination uniformity based on Quasi-sine Particle Swarm Optimization. This paper expatiates the basic principle of arithmetic and its carrying steps firstly. The target function and the orientation degree function are given. The result of optimizing target function shows this arithmetic makes constringency holistically and obtained target illumination by the arithmetic is well-proportioned.

Research on beam smoothing characteristics using linearly modulated light

Precise physical experiments place strict requirements on target illumination uniformity. A new smoothing technology aimed at indirect-drive laser fusion is studied, which uses linearly modulated light and angular spectral dispersion (ASD). Simulation indicates that the best smoothing effect could be obtained when number of color cycles ( N c) is chosen to be 0.5 at 1.2 nm bandwidth. A table-top setup aimed at the experimental study of the beam smoothing method has been established. When the linearly modulated light generated by pulse stacking is dispersed by a grating with N c=2.6, periodical undulations are found on the far-field focal spot, which agrees with the simulation results. To improve illumination uniformity, the N c adopted should be decreased to 0.5. Simulation also indicates that the combination of linearly modulated light, angular spectral dispersion and a continuous phase plate could considerably improve the irradiation nonuniformity.

X-ray and particle diagnostics of a high-density plasma by laser implosion (invited)

A series of laser fusion implosion experiments of plastic hollow shell targets was performed by using the Gekko XII glass laser in order to achieve the required fuel areal density for ignition. Introducing random phase plates to improve illumination uniformity, high-density compression of more than 600 times deuterium liquid density has been achieved. The implosion dynamics and symmetry were observed with a spatially resolved x-ray streak camera and an x-ray multiframing camera. The three-dimensional emission profile of the laser-heated plasma was reconstructed from the x-ray images by use of computed tomography and was compared with the laser illumination profiles. The areal density of the imploded core was measured by the neutron activation of a silicon tracer, the secondary reaction method, and the knock-on proton method. Although the measured density and areal density were consistent with those from 1-D hydrodynamic simulation, experimental neutron yields were significantly lower than those predicted by the simulation for convergence ratios larger than 20. This suggests that better implosion uniformity is required to create a hot spark.