A novel single-pixel imaging (SPI) technique based on discrete orthogonal Zernike moments is proposed. In this technique, the target object is illuminated by two sets of Zernike basis patterns which satisfy the Zernike polynomials. The Zernike moments of object image are obtained by measuring the reflected light intensities with a single-pixel detector. And the object image is reconstructed by summing the product of Zernike polynomials and detected intensities iteratively. By theoretical and experimental demonstration, an image is successfully retrieved under compressive sampling. As for both gray and binary images with resolution of 128×128 pixels, the images reconstructed by Zernike patterns have better image quality compared with those reconstructed by Fourier patterns when sampling ratio is lower than 10%. This technique yields high efficiency and high imaging quality in single-pixel imaging system.
Membrane or film gain mediums have attracted great attention for their good thermal performances and light field manipulation properties, which are helpful for the power scaling of a laser. A membrane laser enabled on the waveguide grating structure is proposed and this design is flexible to manipulate optical properties by controlling the photonic density of states. Lasing behavior is theoretically analyzed based on the four-level rate equations. Results show that pump absorption is enhanced by about 35 times, which leads to improved laser efficiency. When the laser mode overlaps the resonant guided mode, the Purcell factor achieves 212, leading to enhanced emission rate, as well as an apparent decrease of relaxation oscillating amplitude and time delay. The present work offers a preliminary design and lasing behavior analysis of the vertical external surface-emission laser enabled on the waveguide grating structure.
This study demonstrates manipulation of luminance from CaF2: Yb3+, Er3+ up-conversion (UC) micronano particles emissions and the fluorescence intensity improvement by using various surface plasmon resonance substrates which consist of SiO2, gold thin film, and nano cones from bottom to the top in the view of side structure. When they are applied, the optimum enhancement of the intensity of red up-conversion luminescence (UCL) peaked at 653 nm shows up to 189-fold. The distance dependent intensities of two UC micro-nano particles manipulated by holographic optical tweezers (HOT) are also illustrated in this article. The fluorescence intensities decrease when two UC micro-nano particles become near to the each other due to the inter-system transition at the much short distance.
It is difficult to cut through a transparent material such as polyethylene (PE) film with a continuous-wave (CW) laser of the near-infrared wavelength, because of the low absorption of laser energy. The plasma induced by a pulsed laser, however, can damage the surface of a film, which can change the transparency of the material. In this study, a transparent PE film with a thickness of 0.6 mm was irradiated by various combinations of focused laser pulses and a CW laser. The test conditions and the processes were recorded visually by a Schlieren optics system on the side surface of the film and by a high-speed camera on the front surface. From the results, it can be concluded that, though it is difficult to cut through a transparent material such as PE film with only a pulsed or CW laser alone, once the transparency of the surface has been modified by multiple focused laser pulses, the PE film can be cut through easily by a CW laser with a near-infrared wavelength.
The excitation and emission properties of optical materials can be adjusted by nanostructures and to achieve high optical efficiency in the optically pump laser with short absorption length and high threshold pump power, we present and theoretically investigate a Yb-doped thin film on a 1D grating structure in this paper. High reflectivity at the pump and emission wavelength are realized simultaneously and in terms of the guided-mode resonance theory, the local field of high reflected light is enhanced which will increase the absorption of associated laser wavelength. we analyze parameters of the nanostructure in detail based on rigorous coupled-wave theory and an appropriate structure is decided. We set up a simple quasi-three-level model and demonstrate that this designed structure can effectively improve the optical efficiency of optically pump solid state laser.
Atmospheric turbulence induces laser guide star (LGS) spot wandering in the sodium layer, which introduces trouble to adaptive optics systems. Experimental study of LGS spot wandering usually needs on-sky test. However, the on-sky test of LGS spot wandering is expensive and complicated. Since spatial light modulators (SLMs) are able to simulate atmospheric turbulence, we have designed and set up a SLMs based LGS simulator to study LGS spot wandering. This LGS simulator is prominent to build a bridge between theoretical study and on-sky test. Its performance is tested for vortex beam generated annular LGS which was proposed to reduce the LGS spot wandering in our former paper.
We present an annular laser guide star (LGS) concept for large ground-based telescopes in this paper. The more stable annular LGS is generated by turbulence-resisted vortex beam. In the uplink, a vortex beam tends to wander more slightly than a Gaussian beam does in atmospheric turbulence. This may enable an annular LGS to wander more slightly than a traditional Gaussian beam generated LGS does, which would ease the burden of uplink tip-tilt mirror and benefit a dynamical closed-loop adaptive optics system. We conducted numerical simulation to validate the feasibility of this concept. And we have gotten 31% reduced variance of spot wandering of annular LGS. Besides, we set up a spatial light modulator based laser guide star simulator for beam propagation in turbulent atmosphere to experimentally test the annular LGS concept. Preliminary experimental results are given. To the best of our knowledge, it is the first time this concept is formulated.
The Gerschberg-Saxton (GS) algorithm is a classic algorithm for phase retrieval. It is usually based on FFT (fast Fourier
transform) and IFFT (inverse fast Fourier transform). We improve the GS algorithm based on the Wigner distribution.
Instead of FFT and IFFT, Wigner distribution is not only used in the propagation but also filtered to optimize the signal
during the iteration. The simulation results illustrate that the new method could effectively improve the efficiency and
accuracy of phase retrieval.
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