Search

Arc beam laser-induced forward transfer (AB-LIFT) based on an arc beam is a promising micro additive manufacturing process to efficiently prepare high-performance metal microcircuits by transferring metal microdroplets. Therefore, elucidating the transfer mechanism of arc-beam-induced microdroplets is crucial to controlling the printing process. In this paper, a dark-field imaging system is developed to visually analyze the transfer process of metal microdroplets, and the injection mechanism of Gaussian and arc-beam laser-induced forward transfer is analyzed. Meanwhile, by studying the deposition behavior of laser-induced forward transfer micro drops with an arc beam at a single pulse energy, it is concluded that the factors affecting the laser-induced forward transfer with an arc beam mainly include the center angle and diameter of the arc beam. Then the effects of the center angle and diameter of the arc beam and the laser parameters on the preparation of microcircuits by AB-LIFT are systematically investigated, and a set of process methods for the effective preparation of high-performance microcircuits is proposed. [Display omitted] • Developed a dark-field imaging system to visualize and analyze the transfer process under a small receiving gap. • Revealed the formation mechanism of Gaussian beam and Arc beam laser-induced forward transfer. • A set of process methods to effectively fabricate high-performance microcircuits. [ABSTRACT FROM AUTHOR]

• The paper reports the development of a new liquid crystal (LC) optical phase modulator that can lead to full 2 π phase modulation combined with response times that are on the order of 1 ms. • Full 2 π phase modulation can be achieved at driving voltages that are readily accessible using existing silicon backplane technology. • The phase modulator is based on the fast-switching behaviour when operated in the symmetric H state of a nematic pi-cell. • Results are presented demonstrating the electric field conditions required to prolong the stability of the symmetric H state. • The experimental results are found to be in good agreement with results from simulations based upon Ericksen-Leslie continuum theory. In this paper, we investigate the optical phase modulation potential of a nematic liquid crystal (LC) pi-cell operating in the so-called symmetric H (Hs) state. Experimental results of the optical phase modulation obtained using a phase-shifting Michelson interferometer are presented which are then compared with results from simulations carried out using Ericksen-Leslie continuum theory. The stability of the Hs state, which is limited, is investigated by adjusting the amplitude of the applied voltage and the duration of the voltage burst. To achieve full 2π phase modulation with 1 ms timescale in a reflective geometry (akin to that of a spatial light modulator), we employ a short burst voltage to drive the LC pi-cell into the Hs state, which shows excellent phase modulation capability, and the experimental results are found to be in good agreement with the results from simulations. [ABSTRACT FROM AUTHOR]

• A novel technique for quantitative polarimetric evaluation of a spatial light modulator (SLM) using a compact and highly stable Sagnac interferometer. • Complete polarimetric analysis of SLM with varying gray values from 0 to 255. • Experimental demonstration of the proposed technique on the table-top and with external vibrations. • Highly stable and robust experimental geometry applicable even in external disturbances. A compact, stable and lens less digital holographic system is proposed and experimentally demonstrated for a polarimetric analysis of the spatial light modulator (SLM). The experimental design is implemented by using a robust cyclic shearing interferometer consisting of two mirrors and a beam splitter. A polarimetric response of the spatial light modulator with varying gray levels has been characterized by quantitatively extracting the complex fields of the orthogonal polarization components of the light emerging out of the reflective type SLM and results are presented. In order to examine stability of the proposed system, the experiment is performed on a table top and also in the presence of additional external vibrations. These results are compared with earlier results implemented by using a combination of Mach-Zehnder setup along with angular multiplexing of the reference fields. The obtained results indicate that the proposed technique is suitable even under external disturbances. The proposed technique is expected to be beneficial for the polarimetric imaging of objects and in the design of a stable digital holographic system. [ABSTRACT FROM AUTHOR]

We propose a novel approach based on modeled blazed grating (MBG) to realize the mode conversion, multiplexing, demultiplexing, and switching in few-mode transmission fibers. The proposed grating can distribute different modes to different diffraction orders. We demonstrate the generation, multiplexing, demultiplexing, and high efficient conversion and switching of independent coaxial modes in a few-mode transmission fiber using MBG experimentally.

The non-periodic pinhole array filtering of a spatial light modulator (SLM) is proposed for filtering the high-order noise and DC noise of a holographic display. Conventionally, DC and high-order noise sources are filtered by a 4f filtering system. Because the 4f filtering system requires a long optical path length, noise filtering is a stumbling block when attempting to realize a compact holographic display. By contrast, the proposed method simply uses a thin filter fabricated by photolithography. In order to verify this concept, we confirmed the feasibility of the filter with a numerical simulation and with a custom-made non-periodic pinhole array filter used in a practical experiment. The proposed method was shown to have the potential to be used in applications ranging from compact wearable devices to table-top holographic displays.

We report a new mixture, which is modified from Merck TL-216, for liquid-crystal-on-silicon spatial light modulators (SLMs). To achieve 2π phase change at λ = 633 nm with 5 V operation voltage, the measured response time is about 3 ms at 50 °C. Meanwhile, our mixture exhibits no sign of photodegradation and even the total dosage has exceeded 400 MJ/cm2 at a blue laser wavelength λ = 465 nm. In comparison, E7 died at about 30 MJ/cm2. Widespread applications of this material for high brightness SLMs, near-eye displays, and head-up displays are foreseeable.

All of the existing holographic wavefront sensors are either bulky or have low accuracy of measuring wavefront aberrations. In this paper, we present an improvement of the holographic method of measuring wavefront aberrations using computer-generated Fourier holograms. The novelty of this work lies in the proposed approach to the synthesis of Fourier holograms, which are implemented using phase-only SLM. The main advantages of this method are the increased diffraction efficiency compared to the previously known methods, and the more compact implementation scheme due to the elimination of the conventional Fourier-lens. The efficiency of the proposed method was confirmed by numerical simulation and optical experiments.

In this work, we generate optical vortices from the supercontinuum output of an ultrafast laser interacting with a micro-structured fiber. Using a segmented spatial light modulator, multiple vortices are designed and dynamically generated and shifted in order to observe their superposition in the image plane. It is shown that single-color patterns of exquisite complexity can be generated across a wide frequency range. Multi-color interference patterns are experimentally generated and compared to the results of computer simulations. Multiple vortices of varying colors are also generated and independently controlled, demonstrating that no spatial interference occurs. Experimental results are compared with theoretical and numerical simulations, showing excellent agreement.

The phase retrieval method based on random phase modulation can wipe out any ambiguity and stagnation problem in reconstruction. However, the two existing reconstruction algorithms for the random phase modulation method are suffering from problems. The serial algorithm from the spread-spectrum phase retrieval method can realize rapid convergence but has poor noise immunity. Although there is a parallel framework that can suppress noise, the convergence speed is slow. Here, we propose a random phase modulation phase retrieval method based on a serial−parallel cascaded reconstruction framework to simultaneously achieve quality imaging and rapid convergence. The proposed serial−parallel cascaded method uses the phased result from the serial algorithm to serve as the initialization of the subsequent parallel process. Simulations and experiments demonstrate that the superiorities of both serial and parallel algorithms are fetched by the proposed serial−parallel cascaded method. In the end, we analyze the effect of iteration numbers from the serial process on the reconstruction performance to find the optimal allocation scope of iteration numbers.

Progress in laser technology has led to very compact but nevertheless powerful laser sources. In the visible and near infrared spectral region, lasers of any wavelength can be purchased. Continuous wave laser sources pose an especially serious threat to the human eye and electro-optical sensors due to their high proliferation and easy availability. The manifold of available wavelengths cannot be covered by conventional safety measures like absorption or interference filters. We present a protection concept for electro-optical sensors to suppress dazzling in the visible spectral region. The key element of the concept is the use of a digital micromirror device (DMD) in combination with wavelength multiplexing. This approach allows selective spectral filtering in defined regions of interest in the scene. The system offers the possibility of automatic attenuation of dazzling laser radiation.

Whispering-gallery mode microresonators have gained wide popularity as experimental platforms for different applications, ranging from biosensing to nonlinear optics. Typically, the resonant modes of dielectric microresonators are stimulated via evanescent wave coupling, facilitated using tapered optical fibers or coupling prisms. However, this method poses serious shortcomings due to fabrication and access-related limitations, which could be elegantly overcome by implementing a free-space coupling approach; although additional alignment procedures are needed in this case. To address this issue, we have developed a new algorithm to excite the microresonator automatically. Here, we show the working mechanism and the preliminary results of our experimental method applied to a home-made silica microsphere, using a visible laser beam with a spatial light modulator and a software control.