Multi-wavelength pumped upconversion enhancement induced by Cu2-xS plasmonic nanoparticles in NaYF4@Cu2-xS core-shell structure.

Cu2-xS nanoparticles (NPs) demonstrate unique tunable localized surface plasmon resonance (LSPR) and nonlinear optical properties, which are promising materials for photoelectric and display devices. In this work, we present highly improved upconversion luminescence (UCL) in the NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Nd3+@Cu2-xS core-shell structure. The UCL enhancement is systemically studied under excitation of multi-wavelengths 808, 980, and 1540 nm, due to the broadband nature of Cu2-xS LSPR. Two different mechanisms synergistically contribute to the UCL enhancement, namely, the LSPR effect and two-photon effect, which lead to the extraordinary power dependence of UCL. UCL enhancement as high as 12-fold is achieved in the core-shell upconversion NPs (UCNPs). The core-shell NPs are printed on a paper substrate using a nano-printing technique, displaying different colors irradiated by different near-infrared light, and have potential applications in anti-counterfeiting, encryption, and display fields. These findings provide a method to design and optimize luminescent materials and demonstrate potential applications of plasmonic semiconductors and UCNPs.

Surface third and fifth harmonic generation at crystalline Si for non-invasive inspection of Si wafer's inter-layer defects: erratum.

We present an erratum to supplement a missing funding acknowledgment [Pusan National University Research Grant, 2016] in our paper [Y. Gao Opt. Express26(25), 32812 (2018).].

Surface third-harmonic generation at a two-photon-polymerized micro-interferometer for real-time on-chip refractive index monitoring.

A micro-interferometer based on surface third-harmonic generation (THG) at two-photon-polymerized SU-8 cuboids for real-time monitoring of the refractive index changes of target fluids, which can be easily integrated into microfluidic photonic systems, is demonstrated. The third-harmonic (TH) interferogram is selectively generated only from the target volume by a simple vertical pumping, thereby eliminating the needs for complicated coupling and alignments. The dependence of the generated TH to the input pump polarization state is thoroughly investigated. The THG efficiency by linearly polarized excitation is found to be 2.6 × 10-7, which is the most efficient at the SU-8-air interface and independent of the input polarization direction. The THG efficiency from the SU-8-air interface is 12.17 times higher than that from the glass-air interface and 4.93 times higher than that from the SU-8-glass interface. Real-time monitoring of argon gas pressure is demonstrated using the micro- interferometer. The surface TH from two-photon-polymerized 3D structures offers novel design flexibility to the nonlinear optical light sources for microfluidic and microelectronic devices.

Surface third and fifth harmonic generation at crystalline Si for non-invasive inspection of Si wafer's inter-layer defects.

Detection of inter-layer and internal defects in semiconductor silicon (Si) wafers by non-contact, non-destructive and depth-resolving techniques with a high lateral and depth resolution is one of the challenging tasks in modern semiconductor industry. In this paper, we report that nonlinear optical harmonic generation can be of great virtue therein because it enables non-invasive inspection of inter-layer defects with sub-micrometer depth resolution in extensive penetration depth over several millimeters. Compared to existing inspection methods for inter-layer defects, such as ultrasound, photoacoustic and photothermal imaging, the proposed technique provides higher lateral and depth resolution as well as higher interfacial selectivity. For in-depth understanding of nonlinear harmonic generation at Si wafer surfaces, the spectral power distributions of third and fifth harmonics from Si wafers with various crystal orientations and dopants were carefully analyzed under different incident polarizations and excitation depths using a near-infrared (NIR) femtosecond laser as the excitation light source. We finally demonstrated that inter-layer defects inside stacked Si wafers, such as delamination or stacking faults, can be inspected with a high lateral and depth resolution in a non-contact and non-destructive manner. These findings will pave the way for nonlinear optical harmonic generation to the fields of interfacial studies of crystalline materials, high-resolution detection of sub-diffraction-limit surface defects, and high-resolution imaging of internal structures in stacked semiconductor devices.

Linear programming phase unwrapping for dual-wavelength digital holography.

A linear programming phase unwrapping method in dual-wavelength digital holography is proposed and verified experimentally. The proposed method uses the square of height difference as a convergence standard and theoretically gives the boundary condition in a searching process. A simulation was performed by unwrapping step structures at different levels of Gaussian noise. As a result, our method is capable of recovering the discontinuities accurately. It is robust and straightforward. In the experiment, a microelectromechanical systems sample and a cylindrical lens were measured separately. The testing results were in good agreement with true values. Moreover, the proposed method is applicable not only in digital holography but also in other dual-wavelength interferometric techniques.

[Investigation of Multi-Angle Polarization Properties of Vegetation Based on RSP].

Polarization detection provides us with novel information to reflect the target attribute. Compared with traditional remote sensing methods, multi-angle polarization has relatively stable correlation and regularity. RSP(research scanning polarimeter)is an airborne prototype for the APS(aerosol polarimetery sensor) developed by the USA, which can provide with us the polarization detection information of 9 channels. We can get optical properties and physical characteristics of vegetation by analyzing stable multi-angle and multi-band polarization detection information from preprocessing scanning polarization data of flight test. In this paper, after making registration based on flight attitude information, a comparative analysis is made between characteristics of reflectance and polarization reflectance with visible light and near infrared band of the view zenith angles between--30 degree and 65 degree, based on dense area and sparse area(close to bare field) of vegetation. The results show that both dense area and sparse area demonstrate regular characteristics of polarization degree. The area close to hot spot area has highest reflectance energy. In contrast,. it has relatively least energy of polarization degree, which can prevent strong reflectance energy from influencing the stability of detector. Because the degree of polarization in dense area of vegetation is higher than that in sparse area at visible light band while that in concentration area of vegetation is lower than sparse area at near infrared light band, it shows that the visible light band information of dense area of vegetation that the sensor received is dominated by single scattering while the near infrared light band information of dense area of vegetation is dominated by multiple scattering.

[Research on Ground Feature's Polarized Properties with Multi-Spectral and Multi-Angle AirMSPI Data].

Polarization is an important characteristic of electromagnetic wave, and using polarization information to study ground features has been proved to be an effective means. Research on ground feature's polarized properties is an essential part of earth observation. At present, it is in highly need of accurate polarization sensors globally. AirMSPI , (Airborne Multiangle Spectro-Polarimetric Imager) as a new airborne polarized sensor, can obtain multi-band and multi-angle polarization data, and the spatial resolution can reach to ~10 meters. Using the experimental data of Tracy in the year of 2013, this paper analyzes the varying pattern of DOLP (Degree of Linear Polarization) as well as pBRF(polarized Bidirectional Reflectance Factor) in 470 nm, 660 nm, 865 nm bands and 9 view zenith angles. The result shows that, forward scattering of ground features contains plenty of polarized radiation, and ground features present strong non-lambertian effect near principal plane of incidence. DOLP and pBRF has strong correlation to relative position between incidence and view angle. DOLP reaches the maximum value when two directions are perpendicular while pBRF increases with larger view zenith angle. Because of atmospheric effect, radiance of blue band contains most polarized light. However, red and infrared band can attenuate atmospheric molecular polarization scattering effectively, thus contain more polarization details of ground features. Water, artificial structure, residential area, bare soil and vegetation show distinct polarization characteristics, and can be clearly identified. Due to depolarization effect from multi-scattering effect, DOLP and reflected radiation intensity have highly negative correlation, with correlation coefficient generally more than -0.8. AirMSPI sensor can provide high-quality polarization data, as a strong verification to ground-based and satellite-based polarization data, and support parameters inversion of atmosphere and ground features.

Hyperthermia based individual in situ recombinant vaccine enhances lymph nodes drainage for de novo antitumor immunity.

The continuing challenges that limit effectiveness of tumor therapeutic vaccines were high heterogeneity of tumor immunogenicity, low bioactivity of antigens, as well as insufficient lymph nodes (LNs) drainage of antigens and adjuvants. Transportation of in situ neoantigens and adjuvants to LNs may be an effective approach to solve the abovementioned problems. Therefore, an FA-TSL/AuNCs/SV nanoplatform was constructed by integrating simvastatin (SV) adjuvant loaded Au nanocages (AuNCs) as cores (AuNCs/SV) and folic acid modified thermal-sensitive liposomes (FA-TSL) as shells to enhance de novo antitumor immunity. After accumulation in tumor guided by FA, AuNCs mediated photothermal therapy (PTT) induced the release of tumor-derived protein antigens (TDPAs) and the shedding of FA-TSL. Exposed AuNCs/SV soon captured TDPAs to form in situ recombinant vaccine (AuNCs/SV/TDPAs). Subsequently, AuNCs/SV/TDPAs could efficiently transport to draining LNs owing to the hyperthermia induced vasodilation effect and small particle size, achieving co-delivery of antigens and adjuvant for initiation of specific T cell response. In melanoma bearing mice, FA-TSL/AuNCs/SV and laser irradiation effectively ablated primary tumor, against metastatic tumors and induced immunological memory. This approach served a hyperthermia enhanced platform drainage to enable robust personalized cancer vaccination.

Injection-seeded high-repetition-rate short-pulse micro-laser based on upconversion nanoparticles.

We demonstrate a high repetition-rate upconversion green pulsed micro-laser, which is prepared by the fast thermal quenching of lanthanide-doped upconversion nanoparticles (UCNPs) via femtosecond-laser direct writing. The outer rim of the prepared upconversion hemi-ellipsoidal microstructure works as a whispering-gallery-mode (WGM) optical resonator for the coherent photon build-up of third-harmonic ultra-short seed pulses. When near-infrared (NIR) femtosecond laser pulses of wavelength 1545 nm are focused onto the upconversion WGM resonator, the optical third-harmonic is generated at 515 nm together with the upconversion luminescence. The weak third-harmonic (TH) seed pulses are coherently amplified in the hemi-ellipsoidal upconversion resonator as a result of the resonant interaction between the incident femtosecond laser field, the TH, the upconversion luminescence and the WGM. This upconversion lasing preserves the original repetition rate of the NIR pump laser and the output polarization state is also coherently aligned to the pump laser polarization. Because of the isotropic nature of the upconversion micro-ellipsoids, the upconversion lasing shows maximum intensity with a linearly polarized pump beam and minimum intensity with a circularly polarized pump beam. Our scheme devised for realizing high-repetition-rate lasing at higher photon energies in a compact micro platform will open up new ways for on-chip optical information processing, high-throughput microfluidic sensing, and localized micro light sources for optical memories.

Coherent power amplification of third-order harmonic femtosecond pulses at thin-film up-conversion nanoparticles.

Third harmonic generation (THG) is a nonlinear optical process attractive in high-resolution interfacial studies, sub-wavelength light manipulation, and bio-molecular detection due to its capability of converting low-energy quanta into a quantum of a higher energy. One of the limitations in utilizing THG is its low power conversion efficiency; thus, various THG enhancement methods have been researched by involving plasmonic coupling effects or utilizing electric band gap resonances at quantum dots or two-dimensional materials. Meanwhile, lanthanide ion-doped up-conversion nanoparticles (UCNPs) can be excited by a multi-photon process similar to THG, but its interaction or resonance with THG has not been studied to date. In this Communication, we demonstrate the first coherent amplification of third-order harmonic femtosecond pulses at multi-layered UCNP thin-film with an amplification factor of 7.8. This amplification is made by the resonance interaction of incident femtosecond laser field, generated third-order harmonics, and the electric band gaps of UCNPs. The power contribution of the third-order harmonic and the up-conversion luminescence (UCL) is strongly dependent on the sample geometry due to the reabsorption effect. For in-depth understanding of the emission characteristics, spectral-domain, time-domain, radio-frequency (RF) domain, and polarization-dependence analysis were addressed. This coherent amplification of third harmonic (TH) at UCNP thin-films enables us to attain higher power, shorter wavelength, and ultra-short femtosecond pulses generated from a simple thin-film structure near to the target samples, which will pave a way to an ultrafast short-wavelength laser platform for material characterization, sub-wavelength photonics, and biomolecular detection.