Tunable random lasers via phase transition for information encryption.

Introducing phase transition materials to random systems provides a promising route to create new optoelectronic functionalities of random lasers. Here, a phase transition random laser with switchable lasing modes is reported, which is designed with a thermoresponsive hydrogel as scattering medium. By manipulating the phase transition in hydrogel, random lasing modes can be switched reversibility between incoherent and coherent random lasing. The phenomenon derives from the changing of light scattering properties in different phase states, thus affecting the optical feedback path of random lasing. Besides, based on its controllable and easily detectable time-domain characteristics, the phase transition random laser is applied in information encoding and transmission. It is the first time that the transition from coherent to incoherent random lasing is observed by varying the sample phase states. This work will inspire the design and application of novel random lasers in photoelectric device.

Design of reflective phase retarders in the extreme ultraviolet based on chirped Mo/Si multilayer mirrors.

The extreme ultraviolet (EUV) phase retarder is an important optical element for polarization analysis and conversion of EUV synchrotron radiation. In this paper, a linearly chirped Mo/Si multilayer mirror is used to design an EUV phase retarder. With increasing thickness variation of the chirped multilayer, the reflective phase retardation between s- and p-polarized light increases at first and then reaches its maximum value. When the bilayer number increases from 2 to 20, the maximum phase retardation for an EUV source with a photon energy of 90 eV increases from 5.97° to 245.10° for a linearly chirped Mo/Si multilayer with 14.7 nm central thickness. In addition, the phase retardations of chirped mirrors at different photon energies (80 eV, 85 eV and 90 eV) are also investigated and compared. Furthermore, the physical mechanism of reflective phase retardation improvement is also studied by investigating the field intensity distributions inside chirped mirrors.

Sensitivity Improvement of a Surface Plasmon Resonance Sensor Based on Two-Dimensional Materials Hybrid Structure in Visible Region: A Theoretical Study.

In this paper, we propose a surface plasmon resonance (SPR) sensor based on two-dimensional (2D) materials (graphene, MoS2, WS2 and WSe2) hybrid structure, and theoretically investigate its sensitivity improvement in the visible region. The thickness of metal (Au, Ag or Cu) and the layer number of each 2D material are optimized using genetic algorithms to obtain the highest sensitivity for a specific wavelength of incident light. Then, the sensitivities of proposed SPR sensors with different metal films at various wavelengths are compared. An Ag-based SPR sensor exhibits a higher sensitivity than an Au- or Cu-based one at most wavelengths in the visible region. In addition, the sensitivity of the proposed SPR sensor varies obviously with the wavelength of incident light, and shows a maximum value of 159, 194 or 155°/RIU for Au, Ag or Cu, respectively. It is demonstrated that the sensitivity of the SPR sensor based on 2D materials' hybrid structure can be further improved by optimizing the wavelength of incident light.

A reference-defining criterion for light focusing through scattering media based on circular Gaussian distribution of speckle background intensity.

This paper investigates the reference-defining-criterion problem in the field of light focusing through scattering media. In many analogous light focusing experiments, the enhancement values differ greatly from each other. By analyzing the focusing picture after optimizations, we concluded that the discrepancy in enhancement originates from the unclear definition of reference boundary. By averaging multiple speckle backgrounds, we found that the intensity of speckle background obeys circular Gaussian distribution. Based on the intensity statistics and Gaussian-function fitting to the speckle background, we proposed a clear reference-defining criterion- 1/e2 criterion. With this reference-defining criterion, we have carried out light focusing experiments with the speckle backgrounds possessing different shape and size. The enhancements obtained from the repetitive experiments for both weakly scattering medium and strongly scattering medium were all in the reasonable range, demonstrating its validity and universality. This criterion will provide a comparison standard for light focusing experiments in wavefront-shaping field.

Design of broadband reflective circular polarizer for attosecond pulse in the extreme ultraviolet region.

In this paper, we present a design method of broadband reflective circular polarizer (BRCP) in the extreme ultraviolet (EUV) region. By using this method, we designed three BRCPs with a 6, 12 and 18 eV bandwidth, respectively. Then, we investigated the performances of designed BRCPs in theory. The results indicated that the reflected lights of these BRCPs all showed a nearly 100% circular polarization degree and considerable circular reflection in their design band. In addition, we also studied the origin of high circular polarization degree by analyzing the phase shift and the reflectivity ratio between s- and p-polarized lights induced by the reflection of BRCPs. Furthermore, the pulse responses of BRCPs for attosecond pulses were also investigated. The proposed EUV BRCPs can be used for controlling the polarization state of broadband EUV sources, e.g., generating the circularly polarized attosecond pulse by a linearly polarized one.

Figure of Merit Enhancement of a Surface Plasmon Resonance Sensor Using a Low-Refractive-Index Porous Silica Film.

In this paper; the surface plasmon resonance (SPR) sensor with a porous silica film was studied. The effect of the thickness and porosity of the porous silica film on the performance of the sensor was analyzed. The results indicated that the figure of merit (FOM) of an SPR sensor can be enhanced by using a porous silica film with a low-refractive-index. Particularly; the FOM of an SPR sensor with 40 nm thick 90% porosity porous silica film; whose refractive index is 1.04 was improved by 311% when compared with that of a traditional SPR sensor. Furthermore; it was found that the decrease in the refractive index or the increase in the thickness of the low-refractive-index porous silica film can enlarge the FOM enhancement. It is believed that the proposed SPR sensor with a low-refractive-index porous silica film will be helpful for high-performance SPR sensors development.

Research on intelligent algorithms for amplitude optimization of wavefront shaping.

This paper demonstrates further research on intelligent algorithms of binary amplitude optimization for wavefront shaping by numerical simulations. A better fitness function of the genetic algorithm (GA) has been presented after a comparative analysis of enhancement. With this new discriminant, we have achieved a relative enhancement of 0.225, which is higher than the theoretical value (0.159). In addition, we have also proposed a kind of modified particle swarm optimization algorithm (PSO), which has a higher enhancement than the unmodified PSO and a faster convergence speed than the GA. These studies provide remarkable insights into future exploration of intelligent algorithms for wavefront shaping.

Figure of merit enhancement of surface plasmon resonance sensors using absentee layer.

By adding an absentee layer on the top of the metallic layer, the figure of merit (FOM) of a surface plasmon resonance (SPR) sensor with Kretschmann configuration was enhanced, without changing the resonance angle and the reflectance at the resonance angle. Comparing with a traditional SPR sensor, the FOM of the SPR sensor with an absentee layer composed of either 1367 nm thick KCl or 235 nm thick Si3N4 can be improved by 5.53% or 11.41%, respectively. The enhancement of the FOM should be attributed to the faster decrease of the full width at half-maximum than the sensitivity after an absentee layer was applied in the SPR sensor.

[Synthesis and luminiescence of Eu(III) complex based on 4,4,4-trifluoro-1-(4'-m-terphenyl)-1, 3-butanedione and 1,10-phenanthroline].

A new europium (III) complex, EuL3 phen, [HL = 4,4,4-trifluoro-1-(4'-m-terphenyl)-1,3-butanedione, phen = 1, 10-phenanthroline] was synthesized. Its structure was characterized by elemental analysis, IR and FAB-MS. The complex exhibits strongly red emission due to the 5D0-7F(J) (J = 0-4) transitions of Eu3+ ions under irradiation of UV or 395 nm emission light of InGaN chip. The strongest emission peak is located at 613 nm. The luminescence quantum yield is 13%. The lifetime of the complex is 470 micros. The decay curve can be fit with a single exponential. The thermogravimetric analyses curve for the complex shows that the complex is stable up to 220 degrees C, which meets the requirement of fabrication of LED device. A red luminescent LED was successfully fabricated by coating complex EuL3 phen onto 395 nm emitting InGaN chip. The mass ratio of complex to the silicone is related to the chromaticity coordinates and efficiency of fabricated LED. When the mass ratio of complex to the silicone is 1 : 25, the chromaticity coordinates of the fabricated LED with the europium complex are x = 0.64 and y = 0.35 and the efficiency achieves 0.89 lm x W(-1). The results indicate that the complex may act as a potential red component in the fabrication of white LEDs.