Laser-Matter Interaction
2020, 49(12): 20201079.
doi: 10.3788/IRLA20201079
In recent years, the demand for fabrication of 3D metal micro/nanostructures has been rapidly increased in the fields of science and engineering due to their unique physical/chemical properties and flexible configurations. Therefore, various innovative techniques for 3D metal printing at the microscale have been developed, which have attracted intensive attentions. Among those techniques, laser-based assisted 3D metal microprinting exhibits superior performance in terms of its advantages of non-contact processing, flexible patterning capability, and so on. Some of current representative techniques for laser assisted 3D metal microprinting were firstly reviewed from basic principles, technical characteristics, to typical applications. To meet the challenges on fabrication of 3D metal microstructures with high smooth surfaces, high melting points and high conductivities, a glass-microchannel molding technique for assisting 3D metal microprinting was demonstrated. Finally, possible directions and potential applications of laser-assisted 3D metal printing were discussed.
2020, 49(12): 20201057.
doi: 10.3788/IRLA20201057
For many years, silicon and germanium have been considered the suited semiconductor materials for detectors and integrated optoelectronic devices fabrication. However, compared with diamond-based devices, such tetravalent semiconductors are less resistant to radiation damage, and the devices are less stable under harsh conditions or under high-energy light radiation. In recent years, due to the excellent optical and mechanical properties, diamond has become a promising material in the application of integrated photonics, sensors, and quantum optics etc. The laser-induced microstructures of diamond represents a powerful tool used for the development optical 3D-contacts devices all-carbon detectors graphite resistors on diamond, as well as the realization of single photon source. The physical mechanisms of femtosecond laser induced color center, graphitization and refractive index change in diamond were demonstrated. Based on this, the applications of the femtosecond laser induced micro-nano structures in diamond for single photon source, sensor and optical waveguide were introduced. Then, the future developing tendency in this field was prospected.
2020, 49(12): 20201050.
doi: 10.3788/IRLA20201050
Polarization-structured intense laser interacting with nonlinear optical material results in many novel third-order nonlinear optical effects, reflects the nonlinear optical property of the material, and modulates the propagation behavior of the beam itself. Herein, the research progress of third-order nonlinear optical effects excited by vectorial light fields was reviewed. Firstly, the basic theory of third-order nonlinear optical effects excited by arbitrary polarized lights was briefly introduced, such as nonlinear Schrödinger equation, beam propagation equation, and isotropic and anisotropic third-order nonlinear optical coefficients. The Z-scan techniquefor characterizing third-order nonlinear optical coefficients was also introducd. Under the weak focusing condition, the expressions for the focal field of three types of vectorial light fields were provided, i.e., radially polarized beams, hybridly polarized beams, and lemon-type Poincaré beams. Secondly, the isotropic and/or anisotropic third-order nonlinear optical effects excited by a variety of vectorial light fields was revisited, includinganisotropic nonlinear optical effects induced by radially polarized beams, isotropic and anisotropic Kerr nonlinearities excited by hybridly polarized beams, isotropic and anisotropic nonlinear optical effects induced by lemon-type Poincaré beams. Lastly, the prospects of their applications of vectorial light fields in nonlinear polarizationrotation, beam shaping, controllable field collapsing filaments, and optical limiting were briefly discussed.
2020, 49(12): 20201063.
doi: 10.3788/IRLA20201063
Since the advent of perovskite materials, the numerous organic-inorganic hybrid perovskites have thrived vigorously over the decades. Two-dimensional (2D) organic-inorganic hybrid perovskites containing prototypical inorganic octahedron frames and diverse organic cations feature characteristics of intrinsic quantum-well structures and intriguing optoelectronic properties, and have therefore attracted research attention intensively for their optical applications in light emitting, sensing, modulation, photovoltaic cells and telecommunication devices. The low-cost and solution-processed fabrications as well as the alternative organic spacer cations endue 2D hybrid perovskites with flexible layer distances, number of layers, and variable lattice distortion, leading to effectuate the adjustable frameworks as well as higher tunability in optical and photonic applications. In particular, they also demonstrate distinguished and appealing nonlinear optical (NLO) characters whether in the second-order, third-order NLOs or the higher-order NLOs such as second-harmonic generation (SHG), terahertz generation, two-photon absorption (2PA), and saturable absorption (SA), three-photon absorption (3PA), etc., under the excitation of laser pulses. Here, we discuss on the construction of the various 2D hybrid perovskites with different structural features. Furthermore, some representative properties and applications of these 2D hybrid perovskites are discussed in both linear and nonlinear optical regimes. Lastly, the status quo and challenge of 2D hybrid perovskites are elevated, and the future developments of 2D hybrid perovskites is prospected.
2020, 49(12): 20201068.
doi: 10.3788/IRLA20201068
The triplet−triplet annihilation upconversion is a new technology for photonic upconversion, which has the advantages such as continuous wave excitation, tunable upconversion wavelength and high upconversion quantum yields. In this upconversion process, as the energy donor, photosensitizer absorbs the light excitation, and intersystem crossing occurs, then sensitizes the energy acceptor through the triplet−triplet energy transfer process. Finally, the triplet−triplet annihilation of the energy acceptor in the triplet state generates a single excited state which can produce high−efficiency fluorescence (i.e. upconversion luminescence), thus the low−energy light is converted into higher−energy upconversion luminescence, which provides a feasible method for improving the photoelectric conversion efficiency of solar cells or the efficiency of photocatalysis, etc. It is desired to select appropriate lasers to excite the photosensitizer/energy donor system to study the steady upconversion luminescence and the upconversion kinetics. For instance, continuous wave diode pumped solid state laser (DPSSL) was selected as the light source to excite photosensitizer/acceptor system, upconversion luminescence was observed, and the effect of laser power density on upconversion luminescence can be studied conveniently. Additionally, in order to analyze the kinetic process of upconversion luminescence, with optical parametric oscillator (OPO) tunable pulsed laser as the light source, the lifetime of the triplet state, the kinetic characteristics of intermolecular energy transfer and triplet annihilation of photosensitizers can be studied. The application of continuous wave and pulse lasers in triplet–triplet annihilation upconversion experiments was introduced.
2020, 49(12): 20201064.
doi: 10.3788/IRLA20201064
Modification of material surface morphology and properties based on femtosecond laser irradiation is a novel processing technology developed in recent years, which has shown unique advantages in high-speed, large-area and periodic subwavelength structure fabrications. Here this method was employed to rapidly fabricate uniform subwavelength grating structures on the surface of GO film, and then the processing mechanisms, the change of morphology and liquid wettability were investigated comprehensively. Through using different experimental parameters such as the laser power and the scanning speed, the rGO grating structures with variable depth-width ratios and surface "roughness" were obtained, leading to the controllable wettability with the liquid contact angles in a range of 15° to 75°, and their contact angles were found to increase by an average of 20° after 20 days in the air. Our work lays a solid foundation for femtosecond laser micro/nano-processing of two-dimensional materials. It is expected to have the future applications in the field of droplet collection, microfluidic control, and so on.
2020, 49(12): 20201055.
doi: 10.3788/IRLA20201055
Optical fiber surface plasmon resonance (SPR) sensor combines the advantages of optical fiber sensor like miniaturization, online transmission, easy operation and SPR biodetection technology, which is highly sensitive, highly selective and label-free. It is currently a research hotspot of immunological biosensors. However, the signal of traditional multi-mode fiber based SPR sensor is easy to be lost and distorted in long-distance transmission. In this paper, a single mode-no core-single mode fiber based SPR sensor was proposed, which could effectively reduce the loss and distortion in signal transmission, and was suitable for connecting with the current optical fiber network. In order to eliminate the interference signal in the sensor, the core diameter of the no core fiber was changed, the methods of removing background interference and Gaussian fitting were adopted, and finally the sensor with the sensing region of 61.5 μm no core fiber was selected, the effective SPR spectrum signal was extracted from it. The sensitivity of proposed sensor is 1153.40 nm/RIU and the resolution is 1.70×10−4 RIU. The successful development of this kind of optical fiber biosensor provides a new idea for intelligent medical treatment and telemedicine.
2020, 49(12): 20201078.
doi: 10.3788/IRLA20201078
The reported work in 2003-2019 on the reverse saturable absorption (RSA) or two-photon absorption (TPA) and/or optical limiting (OPL) of platinum(II) terpyridine complexes was summarized in this minireview. Photophysical properties, including the ground-state absorption (GSA), excited-state absorption (ESA), excited-state lifetimes, and the quantum yields of triplet excited-state formation, RSA/OPL at 532 nm for ns laser pulses, TPA characteristics in the near-IR spectral regions, and the structure-property correlations were reviewed. This paper is composed of four sections. First, the current status of OPL materials and devices, the general requirements for reverse saturable absorbers and two-photon absorbing materials, and the different types and characteristics of square-planar platinum(II) complexes were briefly introduced. Then the photophysics and RSA/OPL of six series of Pt(Ⅱ) terpyridine-analogous complexes and the structure-property correlations were discussed. Following it the TPA of five series of Pt(Ⅱ) terpyridine complexes and the impacts of structural variations on the TPA cross sections (σ2) were reviewed. Finally, brief conclusions were drawn based on the reported studies. A general trend discovered was that the charge transfer absorption band(s) and the ESA can be readily tuned by substituents on the acetylide or the terpyridine ligand. Introducing electron-donating substituent to the acetylide or terpyridine ligand or improving the coplanarity between the aromatic substituent and the terpyridine ligand red-shifted the ground-state charge-transfer absorption band(s) at the price of decreasing/quenching the triplet ESA, which consequently reduced the RSA/OPL at 532 nm. Extending the π-conjugation of the terpyridine ligand dramatically improved the σ2 values of the Pt(Ⅱ) terpyridine complexes. Incorporation of electron-withdrawing π-conjugated aromatic substituent restrained the GSA to < 500 nm while keeping a long-lived triplet excited state with broadband ESA in the visible spectral regions and moderately strong TPA in the NIR regions. This approach could provide a solution for developing broadband OPL materials.
2020, 49(12): 20201049.
doi: 10.3788/IRLA20201049
The coupling efficiency of non-uniformly correlated beams through atmospheric turbulence was studied. The results show that the fiber coupling efficiency of such beams is higher than that of the traditional Gaussian Schell-model beam; and the regulation of the coherence length of such beams can improve the fiber coupling efficiency; for different transmission distances, the optimization of the coupling efficiency can be achieved by adjusting the coherence length of such beams. Moreover, the effect of the light source parameters: beam waist and wavelength; coupling lens parameters: received aperture and focal length; turbulence intensity on the coupling efficiency of optical fiber was also discussed. The results show that the application of optical field correlation structure manipulation technology in improving the coupling efficiency of optical fiber has important value in the field of free space optical communication.
2020, 49(12): 20201059.
doi: 10.3788/IRLA20201059
Active control of terahertz wave characteristics in stretchable devices is essential for advanced terahertz applications involving large mechanical deformation or stretching. Here, a dual band terahertz active control device based on different mechanisms was designed and fabricated by combining metal metasurface with elastic film polydimethylsiloxane. Based on the deformation mismatch between metal and elastic film under tension, the double band modulation effect was realized by using the periodically sensitive cross structure metasurface. Under 36% deformation, the dipole mode and the lattice resonance mode were exploited to experimentally achieve dual-band modulation with a modulation depth of 90% and a modulation depth of 78% at 1.26 THz and 2.41 THz, respectively. The operating frequency through the lattice mode had a large dynamic range, which could be tuned from 2.41 THz to 1.85 THz. Since the mechanisms of the electric dipole resonance mode and the periodic lattice resonance mode were independent from each other, the two resonance frequencies were designed independently, which allowed the frequency interval of the dual-band modulation to be geometrically adjustable. The stretchable metasurface presented in this paper is simple to prepare, and has the advantages of large intensity modulation depth and wide frequency tuning range. It can be used not only in active control of terahertz wave, but also in passive displacement sensing.
2020, 49(12): 20200398.
doi: 10.3788/IRLA20200398
